Publications by year
In Press
Fyllas NM, Gloor E, Mercado LM, Sitch S, Quesada CA, Domingues TF, Galbraith DR, Torre-Lezama A, Vilanova E, Ramírez-Angulo H, et al (In Press). Analysing Amazonian forest productivity using a new individual and trait-based model (TFS v.1).
Abstract:
Analysing Amazonian forest productivity using a new individual and trait-based model (TFS v.1)
Abstract. Repeated long-term censuses have revealed large-scale spatial patterns in Amazon Basin forest structure and dynamism, with some forests in the west of the Basin having up to a twice as high rate of aboveground biomass production and tree recruitment as forests in the east. Possible causes for this variation could be the climatic and edaphic gradients across the Basin and/or the spatial distribution of tree species composition. To help understand causes of this variation a new individual-based model of tropical forest growth designed to take full advantage of the forest census data available from the Amazonian Forest Inventory Network (RAINFOR) has been developed. The model incorporates variations in tree size distribution, functional traits and soil physical properties and runs at the stand level with four functional traits, leaf dry mass per area (Ma), leaf nitrogen (NL) and phosphorus (PL) content and wood density (DW) used to represent a continuum of plant strategies found in tropical forests. We first applied the model to validate canopy-level water fluxes at three Amazon eddy flux sites. For all three sites the canopy-level water fluxes were adequately simulated. We then applied the model at seven plots, where intensive measurements of carbon allocation are available. Tree-by-tree multi-annual growth rates generally agreed well with observations for small trees, but with deviations identified for large trees. At the stand-level, simulations at 40 plots were used to explore the influence of climate and soil fertility on the gross (ΠG) and net (ΠN) primary production rates as well as the carbon use efficiency (CU). Simulated ΠG, ΠN and CU were not associated with temperature. However all three measures of stand level productivity were positively related to annual precipitation and soil fertility.
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Abstract.
Rosan TM, Goldewijk KK, Ganzenmüller R, O'Sullivan M, Pongratz J, Mercado LM, Aragao LEOC, Heinrich V, Von Randow C, Wiltshire A, et al (In Press). Assessment of land use and land cover datasets for Brazil and impact on C emissions.
Abstract:
Assessment of land use and land cover datasets for Brazil and impact on C emissions
<p>Brazil is responsible for about one third of the global land use and land cover change (LULCC) carbon dioxide emissions. However, there is a disagreement among different methodologies on the magnitude and trends in emissions and their geographic distribution. One of the main uncertainties is associated with different LULCC datatasets used as input in the different approaches. In this work we perform an evaluation of LULCC datasets for Brazil, including the global dataset (HYDE 3.2) used in the annual Global Carbon Budget (GCB), and national Brazilian dataset (MapBiomas) over the period 2000-2018. We also analyze the latest global HYDE 3.3 dataset based on new FAO inventory estimates and multi-annual ESA CCI satellite-based land cover maps. Results show that the new HYDE 3.3 can represent well the observed spatial variation in cropland and pastures areas over the last decades compared to national data (MapBiomas) and shows an improvement compared to HYDE 3.2 used in GCB. However, the magnitude of LULCC assessed with HYDE 3.3 is lower than national estimates from MapBiomas. Finally, we used HYDE 3.3 as input to two different approaches included in GCB, a global bookkeeping model (BLUE) and a process-based Dynamic Global Vegetation Model (JULES-ES) to determine the impact of the new version of HYDE dataset on Brazil’s land-use emissions trends over the period 2000-2017. Both JULES-ES and BLUE now simulate a negative land-use emissions trend for the last two decades. This negative trend is in agreement with Brazilian INPE-EM, global H&N bookkeeping models, FAO and as reported in National GHG inventories (NGHGI), although magnitudes differ among approaches. Overall, the inclusion of the multi-annual ESA CCI Land Cover dataset to allocate spatially the FAO statistical data has improved spatial representation of agricultural area change in Brazil in the last two decades, contributing to improve global model capability to simulate Brazil’s LULCC emissions in agreement with national trends estimates and spatial distribution.</p>
Abstract.
Zelazowski P, Huntingford C, Mercado LM, Schaller N (In Press). Climate pattern scaling set for an ensemble of 22 GCMs – adding
uncertainty to the IMOGEN impacts system.
Abstract:
Climate pattern scaling set for an ensemble of 22 GCMs – adding
uncertainty to the IMOGEN impacts system
Abstract. Global Circulation Models (GCMs) are the best tool to understand climate change, as they attempt to represent all the important Earth system processes, and including anthropogenic perturbation through fossil fuel burning. However, GCMs are computationally very expensive, which limits the number of simulations that can be made. Pattern-scaling is an emulation technique that takes advantage of the fact that local and seasonal changes in surface climate are often approximately linear in amount of warming over land and globe. This allows interpolation away from a limited number of available GCM simulations, to assess alternative future emissions scenarios. In this paper we present a pattern-scaling set consisting of spatial climate change patterns along with parameters for an energy balance model that calculates the amount of global warming. The set is derived from 22 GCMs of the WCRP CMIP3 database, setting the basis for similar eventual pattern development for CMIP5 ensemble. Critically it extends the use of the IMOGEN (Integrated Model of Global Effects of climatic aNomalies) framework to enable scanning across full uncertainty in GCMs for impacts studies. Across models, the presented climate patterns represent consistent global mean trends, with maximum four GCMs exhibiting opposite sign of the trend per variable (relative humidity). The described new climate regimes are generally warmer, wetter (but with less snowfall), cloudier and windier, and with decreased relative humidity. Overall, the patterns of the analysed variables explain one-third of regional change in decadal averages (mean Percentage Variance Explained, PVE, 34.25 ± 5.21), but signal in some models exhibits much more linearity (e.g. MIROC3.2(hires):41.53) than in others (GISS_ER: 22.67). The two most often considered variables: near-surface temperature and precipitation, have PVE of 85.44 ± 4.37 and 14.98 ± 4.61, respectively. The dataset is available for download and researchers in the areas of ecosystem modelling and climate change impact assessment are already starting to use it. Besides allowing time-efficient assessment for non-standard future scenarios of changed greenhouse gas (GHG) concentrations, it enables understanding of new representations of land surface processes, and including climate-carbon cycle feedbacks. Current and potential future applications of such modelling system are discussed.
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Abstract.
Moreira DS, Freitas SR, Bonatti JP, Mercado LM, Rosário NMÉ, Longo KM, Miller JB, Gloor M, Gatti LV (In Press). Coupling between the JULES land-surface scheme and the CCATT-BRAMS atmospheric chemistry model (JULES-CCATT-BRAMS1.0): applications to numerical weather forecasting and the CO<sub>2</sub> budget in South America.
Abstract:
Coupling between the JULES land-surface scheme and the CCATT-BRAMS atmospheric chemistry model (JULES-CCATT-BRAMS1.0): applications to numerical weather forecasting and the CO<sub>2</sub> budget in South America
Abstract. This article presents the development of a new numerical system denominated JULES-CCATT-BRAMS, which resulted from the coupling of the JULES surface model to the CCATT-BRAMS atmospheric chemistry model. The performance of this system in relation to several meteorological variables (wind speed at 10 m, air temperature at 2 m, dew point temperature at 2 m, pressure reduced to mean sea level and 6 h accumulated precipitation) and the CO2 concentration above an extensive area of South America is also presented, focusing on the Amazon basin. The evaluations were conducted for two periods, the wet (March) and dry (September) seasons of 2010. The statistics used to perform the evaluation included bias (BIAS) and root mean squared error (RMSE). The errors were calculated in relation to observations at conventional stations in airports and automatic stations. In addition, CO2 concentrations in the first model level were compared with meteorological tower measurements and vertical CO2 profiles were compared with aircraft data. The results of this study show that the JULES model coupled to CCATT-BRAMS provided a significant gain in performance in the evaluated atmospheric fields relative to those simulated by the LEAF (version 3) surface model originally utilized by CCATT-BRAMS. Simulations of CO2 concentrations in Amazonia and a comparison with observations are also discussed and show that the system presents a gain in performance relative to previous studies. Finally, we discuss a wide range of numerical studies integrating coupled atmospheric, land surface and chemistry processes that could be produced with the system described here. Therefore, this work presents to the scientific community a free tool, with good performance in relation to the observed data and re-analyses, able to produce atmospheric simulations/forecasts at different resolutions, for any period of time and in any region of the globe.
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Abstract.
Mercado L, Restrepo Z, Gonzalez-Caro S, Hartley I, Villegas Palacio J, Meir P (In Press). High vulnerability of highland Andean forests to warming.
Abstract:
High vulnerability of highland Andean forests to warming
Tropical forests are expected to be highly vulnerable to climate change. Observations from the tropical montane Andean forests report a change in composition towards a greater relative abundance of warm affiliated species, i.e thermophilic species. These shifts are hypothesised to result from differential responses to warming of cold- and warm-affiliated species, with the former experiencing mortality and the latter migrating upslope. However, the drivers of these changes are poorly understood. Along a 2000m altitudinal gradient/thermosequence in the Colombian Andes, we planted 2-yr old individuals of cold- and warm-affiliated species under common soil and water conditions, exposing them to the hot and cold extremes of their thermal niches, respectively. We show that cold-affiliated species growing outside and on the hotter portion of their thermal ranges decreased their growth. Warm-affiliated species can survive but reduce their growth under the colder portion of their thermal distribution. We demonstrate that growth responses are related to species&#8217; thermal distributions; survival probability increased as species&#8217; distribution optima were warmer than the experimental site and decreased as species&#8217; distribution optima were colder than the study sites. These results can be explained by the negative effects of heat stress on simulated photosynthesis. &#160;Our findings highlight the potential effects of rapid warming on the composition of highland forest species in this biodiversity hotspot.
Abstract.
Ma Y, Yue X, Sitch S, Unger N, Uddling J, Mercado L, Gong C, Feng Z, Yang H, Zhou H, et al (In Press). Implementation of trait-based ozone plant sensitivity in the Yale Interactive terrestrial Biosphere model v1.0 to assess global vegetation damage.
Abstract:
Implementation of trait-based ozone plant sensitivity in the Yale Interactive terrestrial Biosphere model v1.0 to assess global vegetation damage
Abstract. A major limitation in modeling global ozone (O3) vegetation damage has long been the reliance on empirical O3 sensitivity parameters derived from a limited number of species and applied at the level of plant functional types (PFTs), which ignore the large interspecific variations within the same PFT. Here, we present a major advance in large-scale assessments of O3 plant injury by linking the trait leaf mass per area (LMA) and plant O3 sensitivity in a broad and global perspective. Application of the new approach and a global LMA map in a dynamic global vegetation model reasonably represents the observed interspecific responses to O3 with a unified sensitivity parameter for all plant species. Simulations suggest a contemporary global mean reduction of 4.8 % in gross primary productivity by O3, with a range of 1.1 %–12.6 % for varied PFTs. Hotspots with damages > 10 % are found in agricultural areas in the eastern U.S. western Europe, eastern China, and India, accompanied by moderate to high levels of surface O3. Furthermore, we simulate the distribution of plant sensitivity to O3, which is highly linked with the inherent leaf trait trade-off strategies of plants, revealing high risks for fast-growing species with low LMA, such as crops, grasses and deciduous trees.
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Abstract.
Harper A, Cox P, Friedlingstein P, Wiltshire A, Jones C, Sitch S, Mercado LM, Groenendijk M, Robertson E, Kattge J, et al (In Press). Improved representation of plant functional types and. physiology in the Joint UK Land Environment Simulator. (JULES v4.2) using plant trait information.
Abstract:
Improved representation of plant functional types and. physiology in the Joint UK Land Environment Simulator. (JULES v4.2) using plant trait information
Abstract. Dynamic global vegetation models are used to predict the response of vegetation to climate change. They are essential for planning ecosystem management, understanding carbon cycleclimate feedbacks, and evaluating the potential impacts of climate change on global ecosystems. JULES (the Joint UK Land Environment Simulator) represents terrestrial processes in the UK Hadley Centre family of models and in the first generation UK Earth System Model. Previously, JULES represented five plant functional types (PFTs): broadleaf trees, needle-leaf trees, C3 and C4 grasses, and shrubs. This study addresses three developments in JULES. First, trees and shrubs were split into deciduous and evergreen PFTs to better represent the range of leaf lifespans and metabolic capacities that exists in nature. Second, we distinguished between temperate and tropical broadleaf evergreen trees. These first two changes result in a new set of nine PFTs: tropical and temperate broadleaf evergreen trees, broadleaf deciduous trees, needle-leaf evergreen and deciduous trees, C3 and C4 grasses, and evergreen and deciduous shrubs. Third, using data from the TRY database, we updated the relationship between leaf nitrogen and the maximum rate of carboxylation of Rubisco (Vcmax), and updated the model phenology to include a trade-off between leaf lifespan and leaf mass per unit area.
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Abstract.
Oliver RJ, Mercado LM, Clark DB, Huntingford C, Taylor CM, Vidale PL, McGuire PC, Todt M, Folwell S, Shamsudheen Semeena V, et al (In Press). Improved representation of plant physiology in the JULES-vn5.6 land surface model: Photosynthesis, stomatal conductance and thermal acclimation.
Abstract:
Improved representation of plant physiology in the JULES-vn5.6 land surface model: Photosynthesis, stomatal conductance and thermal acclimation
Abstract. Carbon and water cycle dynamics of vegetation are controlled primarily by photosynthesis and stomatal conductance (gs). Our goal is to improve the representation of these key physiological processes within the JULES land surface model, with a particular focus on refining the temperature sensitivity of photosynthesis, impacting modelled carbon, energy and water fluxes. We test (1) an implementation of the Farquhar et al. (1980) photosynthesis scheme and associated plant functional type-dependent photosynthetic temperature response functions, (2) the optimality-based gs scheme from Medlyn et al. (2011), and (3) the Kattge and Knorr (2007) photosynthetic capacity thermal acclimation scheme. New parameters for each model configuration are adopted from recent large observational datasets that synthesise global experimental data. These developments to JULES incorporate current physiological understanding of vegetation behaviour into the model, and enable users to derive direct links between model parameters and on-going measurement campaigns that refine such parameter values. Replacement of the original Collatz et al. (1991) C3 photosynthesis model with the Farquhar scheme results in large changes in GPP for current-day, with ~10 % reduction in seasonal (June–August; JJA and December–February; DJF) mean GPP in tropical forests, and ~20 % increase in the northern high latitude forests in JJA. The optimality-based gs model decreases the latent heat flux for the present-day (~10 %, with an associated increase in sensible heat flux) across regions dominated by needleleaf evergreen forest in the northern hemisphere summer. Thermal acclimation of photosynthesis coupled with the Medlyn gs scheme reduced tropical forest GPP by up to 5 %, and increased GPP in the high northern latitude forests by between 2 to 5 %. Evaluation of simulated carbon and water fluxes by each model configuration against global data products show this latter configuration generates improvements in these key areas. Thermal acclimation of photosynthesis coupled with the Medlyn gs scheme improved modelled carbon fluxes in tropical and high northern latitude forests in JJA, and improved the simulation of evapotranspiration across much of the northern hemisphere in JJA. Having established good model performance for the contemporary period, we force this new version of JULES offline with a future climate scenario corresponding to rising atmospheric greenhouse gases (SSP5 RCP8.5). In particular, these calculations allow understanding of the effects of long-term warming. We find that the impact of thermal acclimation coupled with the optimality-based gs model on simulated fluxes increases latent heat flux (+50 %) by year 2050 compared to the JULES model configuration without acclimation. This new JULES configuration also projects increased GPP across tropical (+10 %) and northern latitude regions (+30 %) by 2050. We conclude that thermal acclimation of photosynthesis with the Farquhar photosynthesis scheme and the new optimality-based gs scheme together improve the simulation of carbon and water fluxes for current-day, and has a large impact on modelled future carbon cycle dynamics in a warming world.
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Abstract.
Oliver RJ, Mercado LM, Sitch S, Simpson D, Medlyn BE, Lin Y-S, Folberth GA (In Press). Large but decreasing effect of ozone on the European carbon sink.
Abstract:
Large but decreasing effect of ozone on the European carbon sink
Abstract. The capacity of the terrestrial biosphere to sequester carbon and mitigate climate change is governed by the ability of vegetation to remove emissions of CO2 through photosynthesis. Tropospheric O3, a globally abundant and potent greenhouse gas, is, however, known to damage plants, causing reductions in primary productivity, yet the impact of this gas on European vegetation and the land carbon sink is largely unknown. Despite emission control policies across Europe, background concentrations of tropospheric O3 have risen significantly over the last decades due to hemispheric-scale increases in O3 and its precursors. Therefore, plants are exposed to increasing background concentrations, at levels currently causing chronic damage. We use the JULES land-surface model recalibrated for O3 impacts on European vegetation, with an improved stomatal conductance parameterization, to quantify the impact of tropospheric O3, and its interaction with CO2, on gross primary productivity (GPP) and land carbon storage across Europe. A factorial set of model experiments showed that tropospheric O3 can significantly suppress terrestrial carbon uptake across Europe over the period 1901 to 2050. By 2050, simulated GPP was reduced by 4 to 9 % due to plant ozone damage, however, the combined effects of elevated future CO2 (acting to reduce stomatal opening) and reductions in O3 concentrations resulted in reduced O3 damage in the future, contrary to predictions from earlier studies. Reduced land carbon storage resulted from diminished soil carbon stocks consistent with the reduction in GPP. Regional variations are identified with larger impacts shown for temperate Europe compared to boreal regions. These results highlight that the effects of O3 on plant physiology add to the uncertainty of future trends in the land carbon sink and, as such, this should be incorporated into carbon cycle assessments.
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Abstract.
Mercado LM, Medlyn BE, Huntingford C, Oliver R, Clark D, Sitch S, Zelazowski P, Kattge J, Harper A, Cox PM, et al (In Press). Large sensitivity in land carbon storage due to geographical and temporal variation in the thermal response of photosynthetic capacity. New Phytologist
Hancock M, Sitch S, Fischer FJ, Chave J, O'Sullivan M, Fawcett D, Mercado LM (In Press). Modelling the impact of wood density dependent tree mortality on the spatial distribution of Amazonian vegetation carbon.
Abstract:
Modelling the impact of wood density dependent tree mortality on the spatial distribution of Amazonian vegetation carbon
Abstract. Spatially heterogeneous plant mortality rates are an important predictor of the distribution of vegetation carbon in Amazonia. Reproducing the spatial gradients of vegetation carbon in Amazonia and the observed decline in the intact Amazonian carbon sink since 1990 is a challenge faced by dynamic global vegetation models (DGVMs). In this paper, we implement spatially variable mortality rates in TRIFFID, the DGVM currently coupled to the Joint UK Land Environment Simulator (JULES), and compare with the standard model which assumes a homogeneous mortality rate. Spatially variable gridded fields of Amazonian tree mortality are created using a well-known relationship between mortality and wood density, and three independent wood density maps. The diversified mortality scheme substantially improves the representation of vegetation carbon in TRIFFID when compared to observations, with a 90 % reduction in model bias and an increase in the Pearson correlation coefficient with observed biomass. JULES now captures the observed variability of both mortality and vegetation carbon to a greater extent, demonstrating the potential of using easily-measured traits, like wood density, to add spatial and functional diversity into DGVMs. Despite this, the spatial variation of vegetation carbon simulated with the new mortality fields (with standard deviation 15 MgCha-1) is still less than half of the variation in the observed data (standard deviation 35 MgCha-1). Future work should consider the effects of additional processes, like fire, drought and the phosphorus cycle, on the simulated distribution of vegetation carbon in the Amazon.
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Abstract.
Moreira DS, Longo KM, Freitas SR, Yamasoe MA, Mercado LM, Rosário NE, Gloor E, Viana RSM, Miller JB, Gatti LV, et al (In Press). Modelling the radiative effects of smoke aerosols on carbon fluxes in
Amazon.
Abstract:
Modelling the radiative effects of smoke aerosols on carbon fluxes in
Amazon
Abstract. Every year, a dense smoke haze of regional dimensions covers a large portion of South America originated from fire activities in the Amazon Basin and Central parts of Brazil during the dry/biomass-burning season between August and October. Over a large portion of South America, the average aerosol optical depth at 550 nm exceeds 1.0 during the fire season while the background value during the rainy season is below 0.2. Smoke aerosol particles increase scattering and absorption of the incident solar radiation. The regional-scale aerosol layer reduces the amount of solar energy reaching the surface, cools the near surface air, and increases the diffuse radiation fraction over a large disturbed area of the Amazon rainforest. These factors affect the energy and CO2 fluxes at the surface. In this work, we applied a fully integrated atmospheric model to assess the impact of smoke aerosols in CO2 fluxes in the Amazon region during 2010. We address the effects of the attenuation of the solar global radiation and the enhancement of the diffuse solar radiation flux inside the canopy. Our results indicated that the smoke aerosols led to an increase of about 22 % of the gross primary productivity of Amazonia, 9 % of plant respiration and a decline in soil respiration from of 3 %. Consequently, Amazonia net ecosystem exchange during September 2010 dropped from +101 to −104 TgC when the aerosol effects were considered, mainly due to the aerosol diffuse radiation effect. For the forest biome, our results pointed to a dominance of the diffuse radiation effect on CO2 fluxes, reaching a balance of 50 % – 50 % between the diffuse and direct aerosol effects for high aerosol loads. For C3 grass type and cerrado, as expected, the contribution of the diffuse radiation effect is much lower, tending to zero with the increase of aerosol load. That is, the Amazon during the dry season, in the presence of high smoke aerosol loads, change from being a source to be a sink of CO2 to the atmosphere.
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Abstract.
Lugli LF, Andersen KM, Aragao LEOC, Cordeiro AL, Cunha HFV, Fuchslueger L, Meir P, Mercado LM, Oblitas E, Quesada CA, et al (In Press). Multiple phosphorus acquisition strategies adopted by fine roots in low-fertility soils in Central Amazonia. Plant and Soil
Nakhavali AM, Mercado LM, Hartley IP, Sitch S (In Press). Nitrogen and Phosphorus co-limitation impact on temperate forests productivity&#160;.
Abstract:
Nitrogen and Phosphorus co-limitation impact on temperate forests productivity 
&lt;p&gt;Global process-based models with dynamic vegetation and functions show an increasing ongoing land carbon (C) sink, primarily due to CO2 fertilization effects (Sitch et al. 2008; Schimel et al. 2015). However, the phosphorus (P) and Nitrogen (N) related processes may constrain the plant&amp;#8217;s photosynthetic and growth capacity and the C sink magnitude in temperate forests consequently (Aerts and Chapin, 1999; Vitousek et al. 1997; Vitousek, 2004). The co-limitation of N and P changes the plant C fixation capacity and the uptake of the atmospheric CO2 consequently. However, modelling studies are incapable of reproducing the productivity decrease due to these limitations (Fleischer et al. 2019). In this study, we introduced the P dynamics, and its interaction with N and C cycles in the Joint UK Land Environment Simulator (JULES-CNP), and parametrized and calibrated it using a well-site Free-Air Carbon Enrichment (FACE) facility in Mill Haft woodland, England. We further investigate the role of N and P availability and limiting impact on C cycles under different CO2 conditions. Furthermore, we modified the SOC representation in JULES (RothC model) to simulate observed Soil C soil stabilization capacity that is mainly related to soil texture. Our study shows an NPP reduction due to N and P limitation under both ambient and elevated CO2 conditions at the study site. Furthermore, using an improved SOC model in JULES, our results show an increase in soil C turnover with rising CO2 which leads to lower equilibrium soil C stocks than expected from the rise in soil C input alone.&lt;/p&gt;
&lt;p&gt;&amp;#160;&lt;/p&gt;
&lt;p&gt;Reference:&lt;/p&gt;
&lt;p&gt;&amp;#160;&lt;/p&gt;
&lt;p&gt;Aerts, R. and Chapin, F. S.: the Mineral Nutrition of Wild Plants Revisited: a Re-evaluation of Processes and Patterns, Adv. Ecol. Res. 30, 1&amp;#8211;67, https://doi.org/10.1016/S0065-2504(08)60016-1, 1999.&lt;/p&gt;
&lt;p&gt;Fleischer, K. Rammig, A. De Kauwe, M. G. Walker, A. P. Domingues, T. F. Fuchslueger, L. Garcia, S. Goll, D. S. Grandis, A. Jiang, M. Haverd, V. Hofhansl, F. Holm, J. A. Kruijt, B. Leung, F. Medlyn, B. E. Mercado, L. M. Norby, R. J. Pak, B. von Randow, C. Quesada, C. A. Schaap, K. J. Valverde-Barrantes, O. J. Wang, Y.-P. Yang, X. Zaehle, S. Zhu, Q. and Lapola, D. M.: Amazon forest response to CO2 fertilization dependent on plant phosphorus acquisition, Nat. Geosci. 12, 736&amp;#8211;741, https://doi.org/10.1038/s41561-019-0404-9, 2019.&lt;/p&gt;
&lt;p&gt;Vitousek, P. M.: Nutrient Cycling and Limitation: Hawai&amp;#8217;i as a Model System, Princeton University Press, 2004.&lt;/p&gt;
&lt;p&gt;Vitousek, P. M. Mooney, H. A. Lubchenco, J. M. and Melillo, J. M.: Human Domination of Earth Ecosystems, Science (80-. ). 278, 21, 1997.&lt;/p&gt;
&lt;p&gt;&amp;#160;&lt;/p&gt;
Abstract.
Sarangi C, Chakraborty T, Tripathi S, Krishnan M, Morrison R, Evans J, Mercado L (In Press). Observations of Aerosol-Vapor Pressure Deficit-Evaporative Fraction coupling over India.
Abstract:
Observations of Aerosol-Vapor Pressure Deficit-Evaporative Fraction coupling over India
Abstract. North India is a densely populated subtropical region with heavy aerosol loading, frequent heatwaves and strong atmosphere-biosphere coupling, making it ideal for studying the impacts of aerosols and temperature variation on latent heat flux (LH) and evaporative fraction (EF). Here, using in situ observations during the onset of the summer monsoon over a semi-natural grassland site in this region, we confirm that strong co-variability exists among aerosols, LH, air temperature (Tair) and vapor pressure deficit (VPD). Since the surface evapotranspiration is strongly controlled by both physical (available energy and moisture demand) and physiological (canopy and aerodynamic resistance) factors, we separately analyze our data for different combinations of aerosols and Tair/VPD changes. We find that aerosol loading and heatwave conditions both reduces SH. Further, we find that an increase in atmospheric VPD, tends to decrease the gross primary production (GPP) and thus LH, most likely as a response to stomatal closure of the dominant grasses at this location. In contrast, under heavy aerosol loading, LH is enhanced partly due to the physiological control exerted by the diffuse radiation fertilization effect (thus increasing EF). Moreover, LH and EF are positively associated with aerosol loading even under heatwave conditions, indicating a decoupling of plant’s response to VPD enhancement (stomatal closure) in presence of high aerosol conditions. With heat-stress, VPD and aerosols expected to increase in future India, our results warrant in-depth analysis of aerosol-plant-temperature-EF continuum and its impact on Indian monsoon dynamics and crop vulnerability.
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Abstract.
Sitch S, Cheesman AW, Brown F, Artaxo P, Cernusak LA, Folberth G, Hayes F, Hill T, Mercado L, Uddling J, et al (In Press). Ozone impacts on tropical forest productivity.
Abstract:
Ozone impacts on tropical forest productivity
Tropospheric ozone (O3) reduces plant productivity by entering leaves, generating reactive oxygen species and causing oxidative stress which in turn increases respiration, decreases photosynthesis, plant growth, biomass accumulation, and consequently reduces the land carbon sink. Tropical forests are potentially most vulnerable to future O3 scenarios given their high productivity, generally high stomatal conductance and environmental conditions conducive to O3 uptake (eg precursor emissions during biomass burning).Here we present the first comprehensive set of measurements of O3 effects on plant physiology and biomass accumulation in tropical forests. We exposed twelve tropical tree species to elevated O3 concentrations in Open Top Chambers (OTCs) based at the James Cook University O3 experimental facility in Cairns, Australia, from which we generate O3 dose-response functions for each species. We test the importance of Leaf Mass per unit Area (LMA) as an indicator of O3 sensitivity.We use these relationships to parameterize the global land-surface model JULES, and apply the model over the pan-tropical region using contemporary near-surface O3 concentration fields. For the first time we quantify the impact of O3 on contemporary tropical productivity.
Abstract.
Wong CYS, Mercado LM, Arain MA, Ensminger I (In Press). Remotely sensed carotenoid dynamics predict photosynthetic phenology in conifer and deciduous forests.
Abstract:
Remotely sensed carotenoid dynamics predict photosynthetic phenology in conifer and deciduous forests
AbstractCrucially, the phenology of photosynthesis conveys the length of the growing season. Assessing the timing of photosynthetic phenology is key for terrestrial ecosystem models for constraining annual carbon uptake. However, model representation of photosynthetic phenology remains a major limitation. Recent advances in remote sensing allow detecting changes of foliar pigment composition that regulate photosynthetic activity. We used foliar pigments changes as proxies for light-use-efficiency (LUE) to model gross primary productivity (GPP) from remote sensing data. We evaluated the performance of LUE-models with GPP from eddy covariance and against MODerate Resolution Imaging Spectroradiometer (MODIS) GPP, a conventional LUE model, and a process-based dynamic global vegetation model at an evergreen needleleaf and a deciduous broadleaf forest. Overall, the LUE-models using foliar pigment information best captured the start and end of season, demonstrating that using regulatory carotenoids and photosynthetic efficiency in LUE models can improve remote monitoring of the phenology of forest vegetation.
Abstract.
Williams KE, Harper AB, Huntingford C, Mercado LM, Mathison CT, Falloon PD, Cox PM, Kim J (In Press). Revisiting the First ISLSCP Field Experiment to evaluate water
stress in JULESv5.0.
Abstract:
Revisiting the First ISLSCP Field Experiment to evaluate water
stress in JULESv5.0
Abstract. The First ISLSCP Field Experiment (FIFE), Kansas, US, 1987–1989, made important contributions to the understanding of energy and CO2 exchanges between the land-surface and the atmosphere, which heavily influenced the development of numerical land-surface modelling. Thirty years on, we demonstrate how the wealth of data collected at FIFE and its subsequent in-depth analysis in the literature continues to be a valuable resource for the current generation of land-surface models. To illustrate, we use the FIFE dataset to evaluate the representation of water stress on tallgrass prairie vegetation in the Joint UK Land Environment Simulator (JULES) and highlight areas for future development. We show that, while JULES is able to simulate a decrease in net carbon assimilation and evapotranspiration during a dry spell, the shape of the diurnal cycle is not well captured. Evaluating the model parameters and results against this dataset provides a case study on the assumptions in calibrating "unstressed" vegetation parameters and thresholds for water stress. In particular, the response to low water availability and high temperatures are calibrated separately. We also illustrate the effect of inherent uncertainties in key observables, such as leaf area index, soil moisture and soil properties. Given these valuable lessons, simulations for this site will be a key addition to a compilation of simulations covering a wide range of vegetation types and climate regimes, which will be used to improve the way that water stress is represented within JULES.
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Abstract.
Malavelle FF, Haywood JM, Mercado LM, Folberth GA, Bellouin N, Sitch S, Artaxo P (In Press). Studying the impact of biomass burning aerosol radiative and climate effects on the Amazon rainforest productivity with an Earth System Model.
Abstract:
Studying the impact of biomass burning aerosol radiative and climate effects on the Amazon rainforest productivity with an Earth System Model
Abstract. Diffuse light conditions can increase the efficiency of photosynthesis and carbon uptake by vegetation canopies. The diffuse fraction of photosynthetically active radiation (PAR) can be affected by either a change in the atmospheric aerosol burden and/or a change in cloudiness. During the dry season, a hotspot of Biomass Burning on the edges of the Amazon rainforest emits a complex mixture of aerosols and their precursors and climate-active trace gases (e.g. CO2, CH4, NOx etc). This creates potential for significant interactions between chemistry, aerosol, cloud, radiation and the biosphere across the Amazon region. The combined effects of biomass burning on the terrestrial carbon cycle for the present-day are potentially large, yet poorly quantified. Here, we quantify such effects using the Met Office Hadley Centre Earth System Model HadGEM2-ES which provides a fully coupled framework with interactive aerosol, radiative transfer, dynamic vegetation, atmospheric chemistry and biogenic volatile organic compound emission components. Results show that the overall net impact of present-day biomass burning aerosols is to increase net primary productivity (NPP) by +80 to +105 TgC/yr, or 1.9 to 2.7 %, over the central Amazon basin on annual mean. For the first time we show that this enhancement is the net result of multiple competing effects: an increase in diffuse light which stimulates photosynthetic activity in the shaded part of the canopy (+65 to +110 TgC/yr), a reduction in the total amount of radiation (−52 to −105 TgC/yr) which reduces photosynthesis and feedback from climate adjustments in response to the aerosol forcing which increases the efficiency of biochemical processes (+67 to +100 TgC/yr). These results illustrate that despite a modest direct aerosol effect (the sum of the first two counteracting mechanisms) the overall, net impact of biomass burning aerosols on vegetation, is sizeable, when indirect climate feedbacks are considered. We demonstrate that capturing the net impact of aerosols on vegetation should be assessed considering the system-wide behaviour.
.
Abstract.
Ma Y, Yue X, Sitch S, Unger N, Uddling J, Mercado L, Gong C, Feng Z, Yang H, Zhou H, et al (In Press). Supplementary material to "Implementation of trait-based ozone plant sensitivity in the Yale Interactive terrestrial Biosphere model v1.0 to assess global vegetation damage".
Fyllas NM, Gloor E, Mercado LM, Sitch S, Quesada CA, Domingues TF, Galbraith DR, Torre-Lezama A, Vilanova E, Ramírez-Angulo H, et al (In Press). Supplementary material to &quot;Analysing Amazonian forest productivity using a new individual and trait-based model (TFS v.1)&quot;.
Zelazowski P, Huntingford C, Mercado LM, Schaller N (In Press). Supplementary material to &quot;Climate pattern scaling set for an ensemble of 22 GCMs – adding
uncertainty to the IMOGEN impacts system&quot;.
Moreira DS, Freitas SR, Bonatti JP, Mercado LM, Rosário NMÉ, Longo KM, Miller JB, Gloor M, Gatti LV (In Press). Supplementary material to &quot;Coupling between the JULES land-surface scheme and the CCATT-BRAMS atmospheric chemistry model (JULES-CCATT-BRAMS1.0): applications to numerical weather forecasting and the CO&lt;sub&gt;2&lt;/sub&gt; budget in South America&quot;.
Harper A, Cox P, Friedlingstein P, Wiltshire A, Jones C, Sitch S, Mercado LM, Groenendijk M, Robertson E, Kattge J, et al (In Press). Supplementary material to &quot;Improved representation of plant functional types and. physiology in the Joint UK Land Environment Simulator. (JULES v4.2) using plant trait information&quot;.
Oliver RJ, Mercado LM, Clark DB, Huntingford C, Taylor CM, Vidale PL, McGuire PC, Todt M, Folwell S, Shamsudheen Semeena V, et al (In Press). Supplementary material to &quot;Improved representation of plant physiology in the JULES-vn5.6 land surface model: Photosynthesis, stomatal conductance and thermal acclimation&quot;.
Oliver RJ, Mercado LM, Sitch S, Simpson D, Medlyn BE, Lin Y-S, Folberth GA (In Press). Supplementary material to &quot;Large but decreasing effect of ozone on the European carbon sink&quot;.
Sarangi C, Chakraborty T, Tripathi S, Krishnan M, Morrison R, Evans J, Mercado L (In Press). Supplementary material to &quot;Observations of Aerosol-Vapor Pressure Deficit-Evaporative Fraction coupling over India&quot;.
Nakhavali M, Mercado LM, Hartley IP, Sitch S, Cunha FV, di Ponzio R, Lugli LF, Quesada CA, Andersen KM, Chadburn SE, et al (In Press). Supplementary material to &quot;Representation of phosphorus cycle in Joint UK Land Environment Simulator (vn5.5_JULES-CNP)&quot;.
Malavelle FF, Haywood JM, Mercado LM, Folberth GA, Bellouin N, Sitch S, Artaxo P (In Press). Supplementary material to &quot;Studying the impact of biomass burning aerosol radiative and climate effects on the Amazon rainforest productivity with an Earth System Model&quot;.
Harper AB, Wiltshire AJ, Cox PM, Friedlingstein P, Jones CD, Mercado LM, Sitch S, Williams K, Duran-Rojas C (In Press). Supplementary material to &quot;Vegetation distribution and terrestrial carbon cycle in. a carbon-cycle configuration of JULES4.6 with new plant functional types&quot;.
Huntingford C, Oliver RJ, Mercado LM, Sitch S (In Press). Technical Note: a simple theoretical model framework to describe plant stomatal sluggishness in response to elevated ozone concentrations.
Abstract:
Technical Note: a simple theoretical model framework to describe plant stomatal sluggishness in response to elevated ozone concentrations
Abstract. Elevated levels of tropospheric Ozone [O3] causes damage to terrestrial vegetation, affecting leaf stomatal functioning and reducing photosynthesis. Climatic impacts under future raised atmospheric Greenhouse Gas (GHG) concentrations will also impact on the Net Primary Productivity (NPP) of vegetation, which might for instance alter viability of some crops. Together, ozone damage and climate change may adjust the current ability of terrestrial vegetation to offset a significant fraction of carbon dioxide (CO2) emissions. Climate impacts on the land surface are well studied, but arguably large-scale modelling of raised surface level [O3] effects is less advanced. To date most models representing ozone damage use either [O3] concentration or, more recently, flux-uptake related reduction of stomatal opening, estimating suppressed land-atmosphere water and CO2 fluxes. However there is evidence that for some species, [O3] damage can also cause an inertial sluggishness of stomatal response to changing surface meteorological conditions. In some circumstances e.g. droughts, this loss of stomata control can cause them to be more open than without ozone interference. The extent of this effect may be dependent on magnitude and cumulated time of exposure to raised [O3], suggesting experiments to analyze this require operation over long timescales such as full growing seasons. To both aid model development and provide empiricists with a system on to which measurements can be mapped, we present a parameter-sparse framework specifically designed to capture sluggishness. This contains a single time-delay parameter τO3, characterising the timescale for stomata to catch up with the level of opening they would have with- out damage. The larger the value of this parameter, the more sluggish the modelled stomatal response. Through variation of τO3, we find it is possible to have qualitatively similar responses to factorial experiments with and without raised [O3], when comparing to measurement timeseries presented in the literature. This low-parameter approach lends itself to the inclusion of ozone-induced inertial effects being incorporated in the terrestrial vegetation component of Earth System Models (ESMs).
.
Abstract.
Rosan TM, Sitch S, O’Sullivan M, Wilson C, Basso LS, Fawcett D, Heinrich VA, Souza JG, von Randow C, Mercado LM, et al (In Press). The contemporary Amazon Forest carbon budget.
Abstract:
The contemporary Amazon Forest carbon budget
The Amazon is the largest continuous tropical forest in the world and plays a key role in the global carbon cycle. Human-induced disturbances (e.g. deforestation and wildfires) in combination with climate change have impacted its carbon cycling. However, uncertainties remain on the magnitude of carbon fluxes associated with human-induced disturbances and the old-growth forest sink, and thus the net land carbon balance of the Amazon. Here we synthesize state-of-the-art estimates of the land carbon flux components in the Amazon. To quantify the human-disturbance fluxes from deforestation, land use and land cover changes and degradation, we use a set of bookkeeping models. The annual intact sink was quantified using a set of 16 Dynamic Global Vegetation Models (DGVMs). We then combine the carbon flux estimates from disturbances with the intact sink estimates to provide a bottom-up estimate of the net land carbon flux and compare them alongside top-down estimates from atmospheric model inversions. Between 2010 and 2018, the net land carbon flux in the Brazilian Amazon estimated with the bottom-up approach was -59 (&#177;160) Tg C yr-1 and +36 (&#177;125) Tg C yr-1 with the top-down approach. Despite disagreeing on the sign of the flux, this analysis suggests that the Brazilian Amazon was on average near carbon neutral over the 2010-2018 period, given the large uncertainties underlying both methods. The net land carbon fluxes for the years 2019 and 2020 based on the bottom-up approach were larger than for 2010-2018. This is likely primarily due to direct emissions related to an increase in deforestation although it may possibly be partly caused by a weakening of the forest carbon sink, both in response to deforestation and a warming climate. Spatially, both methodologies agree that the south-eastern Amazon was a net carbon source over the whole study period. These results have important implications for the mitigation potential of Brazilian ecosystems within the goals of the Paris Agreement.&#160;&#160;
Abstract.
Oliver R, Mercado L, Clark D, Harris P, Medlyn B (In Press). The future of forests: thermal acclimation in the JULES land surface model.
Abstract:
The future of forests: thermal acclimation in the JULES land surface model
A key driver of the terrestrial carbon sink is photosynthesis. Accurate representation of this process in Earth System models is important to help understand and quantify the resilience of the global carbon sink to future climate change. In the JULES land surface model (the land surface component of the UK Earth System model - UKESM), we implement thermal adaptation and acclimation of photosynthesis using the latest scheme from Kumarathunge et al. (2019), which is based on data from 141 C3 species covering a diverse range of biomes from tropical rainforest to arctic tundra. Additionally, we explore the sensitivity of photosynthetic acclimation to rising atmospheric CO2 concentrations. In model simulations using forcing based on RCP8.5 to explore the model response to increasing temperatures, we show that thermal adaptation and acclimation has a positive effect on GPP that persists to 2050, but the size of the response diminishes over time. Broken down by biome, this effect is most notable in the tropics. Additionally, opposite effects of temperature adaptation and acclimation are seen in tropical (adaptation effect decreases GPP over time, whereas acclimation increases GPP) versus temperate and boreal regions (adaptation effect is constant, whereas acclimation decreases GPP over time). The attenuation of the adaptation effect in the tropics is because high temperatures in this region cause a shift in the Jmax:Vcmax ratio such that photosynthesis becomes light-limited earlier (in contrast to simulations where thermal adaptation and acclimation is not activated). The light-limited rate of photosynthesis is less sensitive to increasing atmospheric CO2 concentrations, therefore photosynthetic rates are reduced. This effect is not seen in the temperate/boreal regions because of the cooler temperatures here. Thermal acclimation results in seasonal shifts in the optimum temperature for photosynthesis. In the tropics, the optimum temperature for photosynthesis increases compared to control simulations without acclimation allowing for higher photosynthetic rates at leaf temperatures around the optimum. This increases the resilience of tropical vegetation to higher temperatures and heat extremes. In the temperate and boreal region, thermal acclimation lowers the optimum temperature for photosynthesis to adjust photosynthetic capacity to cooler spring temperatures. Acclimation of the Jmax:Vcmax ratio to increasing atmospheric CO2 concentration results in large decreases in GPP as CO2 concentrations rise across all biomes. Enabling thermal adaptation and acclimation in the JULES land surface model therefore leads to a lower CO2 fertilisation response of tropical vegetation as photosynthesis transitions from CO2-limited to light-limited earlier, however vegetation productivity benefits from adjustment of its thermal sensitivity of photosynthesis to local temperatures.
Abstract.
Stacey J, Betts R, Hartley A, Mercado L (In Press). The importance of the plant physiological response to rising CO2 in projections of future water availability.
Abstract:
The importance of the plant physiological response to rising CO2 in projections of future water availability
Reliable and useful future projections of water scarcity are vital for incorporating into climate policy and national adaptation plans for building climate resilience. However, projections of water scarcity are often based on hydrology models which do not include an important climate feedback affecting the water cycle: the response of plant physiology to rising atmospheric CO2, or &#8220;physiological forcing&#8221;. With higher atmospheric CO2, plant physiology can affect the water cycle in two contradictory ways. Plant stomata do not open as widely in higher CO2, and therefore transpiration rates are lower, leaving relatively more water in the ground increasing runoff and soil moisture. However, faster rates of photosynthesis with higher CO2 also encourages greater leaf area, and thus higher overall canopy transpiration (even though transpiration of an individual stomata still decreases). The influence of physiological forcing on physical quantities within the water cycle such as transpiration and runoff have been well studied; however, there is a requirement to quantify how this translates to human impacts and more policy-relevant metrics on water resources, such as the water scarcity index. I will present findings from experiments using the Joint UK Land Environmental Simulator (JULES) forced with four earth system models which quantify and highlight the importance of including the plant physiological response in water-related impact studies.
Abstract.
Ma Y, Yue X, Sitch S, Unger N, Uddling J, Mercado L, Gong C, Feng Z (In Press). Trait-based ozone plant sensitivity to assess global vegetation damage risks.
Abstract:
Trait-based ozone plant sensitivity to assess global vegetation damage risks
A major limitation in modeling global O3 vegetation damage has long been the reliance on empirical O3 sensitivity parameters derived from a limited number of species and applied at the level of plant functional types (PFTs), which ignore the large interspecific variations within the same PFT. Here, we present a major advance in large-scale assessments of O3 plant injury by linking the trait leaf mass per area (LMA) and plant O3 sensitivity in a broad and global perspective. Application of the new approach and a global LMA map in a dynamic global vegetation model reasonably represents the observed interspecific responses to O3 with a unified sensitivity parameter for all plant species. Simulations suggest a contemporary global mean reduction of 4.8% in gross primary productivity by O3, with a range of 1.1%-12.6% for varied PFTs. Hotspots with damages > 10% are found in agricultural areas in the eastern U.S. western Europe, eastern China, and India, accompanied by moderate to high levels of surface O3. Furthermore, we reveal an inherent plant sensitivity spectrum for O3 which is highly linked with plant leaf trait trade-off strategy, revealing high risks for fast-growing species with low LMA, such as crops, grasses and deciduous trees.
Abstract.
Harper AB, Wiltshire AJ, Cox PM, Friedlingstein P, Jones CD, Mercado LM, Sitch S, Williams K, Duran-Rojas C (In Press). Vegetation distribution and terrestrial carbon cycle in. a carbon-cycle configuration of JULES4.6 with new plant functional types.
Abstract:
Vegetation distribution and terrestrial carbon cycle in. a carbon-cycle configuration of JULES4.6 with new plant functional types
Abstract. Dynamic global vegetation models (DGVMs) are used for studying historical and future changes to vegetation and the terrestrial carbon cycle. JULES (the Joint UK Land Environment Simulator) represents the land surface in the Hadley Centre climate models and in the UK Earth System Model. Recently the number of plant functional types (PFTs) in JULES were expanded from 5 to 9 to better represent functional diversity in global ecosystems. Here we introduce a more mechanistic representation of vegetation dynamics in TRIFFID, the dynamic vegetation component of JULES, that allows for any number of PFTs to compete based solely on their height, removing the previous hardwired dominance hierarchy where dominant types are assumed to outcompete subdominant types. With the new set of 9 PFTs, JULES is able to more accurately reproduce global vegetation distribution compared to the former 5 PFT version. Improvements include the coverage of trees within tropical and boreal forests, and a reduction in shrubs, which dominated at high latitudes. We show that JULES is able to realistically represent several aspects of the global carbon cycle. The simulated gross primary productivity (GPP) is within the range of observations, but simulated net primary productivity (NPP) is slightly too high. GPP in JULES from 1982–2011 was 133 PgC yr−1, compared to observation-based estimates between 123±8 (over the same time period) and 150–175 PgC yr−1. NPP from 2000–2013 was 72 PgC yr−1, compared to satellite-derived NPP of 55 PgC yr−1 over the same period and independent estimates of 56.2±14.3 PgC yr−1. The simulated carbon stored in vegetation is 542 PgC, compared to an observation-based range of 400–600 PgC. Soil carbon is much lower (1422 PgC) than estimates from measurements (>2400 PgC), with large underestimations of soil carbon in the tropical and boreal forests. We also examined some aspects of the historical terrestrial carbon sink as simulated by JULES. Between the 1900s and 2000s, increased atmospheric carbon dioxide levels enhanced vegetation productivity and litter inputs into the soils, while land-use change removed vegetation and reduced soil carbon. The result was a simulated increase in soil carbon of 57 PgC but a decrease in vegetation carbon by of PgC. JULES simulated a loss of soil and vegetation carbon of 14 and 124 PgC, respectively, due to land-use change from 1900–2009. The simulated land carbon sink was 2.0±1.0 PgC yr−1 from 2000–2009, in close agreement to estimates from the IPCC and Global Carbon Project.
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Abstract.
Ocampo Montoya E, Nottingham AT, Villegas Palacio JC, Mercado LM, Restrepo Z, Meir P (In Press). Warming effects on soil CO2 efflux in the tropical Andes: Insights from an experimental thermosequence with dominant tree species.
Abstract:
Warming effects on soil CO2 efflux in the tropical Andes: Insights from an experimental thermosequence with dominant tree species.
&lt;p&gt;Tropical forests, while only occupying 12% to 15% of the Earth's surface, contain about 25% of the world's carbon biomass, with soils representing the second largest reservoir. Yet, recent studies have suggested that, in response to changing environmental conditions, in future decades tropical forests can switch from carbon sinks to carbon sources, with profound implications for the global carbon cycle. Most of these conclusions result from studies in lowland humid forests. However, other tropical forests, such as those occurring in the Andes are also important determinants of regional-to-global biogeochemical functioning, and their sensitivity to future warming has been less studied than in lowland forests. In this study, we explore intra and interspecific thermal sensitivity of soil respiration and its components (autotrophic and heterotrophic) in 15 dominant tree species in the tropical Andes, through an experimental thermosecuence in the Colombian Andes that uses elevation as a proxy for warming. In this thermosequence, a common garden experiment was set up and individuals from 15 dominant species were planted in three sites that represent a temperature gradient: the higher elevation site (2452 masl) corresponds to the base condition; the mid-elevation site (1326 masl) represents a warming of 8&amp;#176;C; and the lower site (575 masl) and it represents a warming of 12&amp;#176;C. Our results indicate consistently higher respiration values with increased temperature both within and between tree species. We used &amp;#119928;&lt;sub&gt;10&lt;/sub&gt; values (the factor by which soil respiration increases for every 10-degree rise in temperature) to determine the temperature sensitivity of soil respiration. More specifically, for a warming of 5&amp;#176;C there is a temperature coefficient of &amp;#119928;&lt;strong&gt;&lt;sub&gt;10&lt;/sub&gt;&lt;/strong&gt; = 2 and for a warming of 9&amp;#176;C and there is a temperature coefficient &amp;#119928;&lt;sub&gt;10&lt;/sub&gt; = 3, this means that for the greater increase temperature the soil respiration can increase faster. Notably, our results show that not all species respond equally to augmented temperatures, highlighting the potential for differential effects of increased temperature and more generally, of environmental change in the compositions and function of these strategic ecosystems. Collectively, our results are relevant for the management and adaptation of ecosystems, particularly tropical Andean forest, and for the refinement of ecological models that support projections of global environmental change and carbon cycle.&amp;#160;&lt;/p&gt;
Abstract.
2023
Cox AJF, Hartley IP, Meir P, Sitch S, Dusenge ME, Restrepo Z, González-Caro S, Villegas JC, Uddling J, Mercado LM, et al (2023). Acclimation of photosynthetic capacity and foliar respiration in Andean tree species to temperature change.
New Phytol,
238(6), 2329-2344.
Abstract:
Acclimation of photosynthetic capacity and foliar respiration in Andean tree species to temperature change.
Climate warming is causing compositional changes in Andean tropical montane forests (TMFs). These shifts are hypothesised to result from differential responses to warming of cold- and warm-affiliated species, with the former experiencing mortality and the latter migrating upslope. The thermal acclimation potential of Andean TMFs remains unknown. Along a 2000 m Andean altitudinal gradient, we planted individuals of cold- and warm-affiliated species (under common soil and irrigation), exposing them to the hot and cold extremes of their thermal niches, respectively. We measured the response of net photosynthesis (Anet ), photosynthetic capacity and leaf dark respiration (Rdark ) to warming/cooling, 5 months after planting. In all species, Anet and photosynthetic capacity at 25°C were highest when growing at growth temperatures (Tg ) closest to their thermal means, declining with warming and cooling in cold-affiliated and warm-affiliated species, respectively. When expressed at Tg , photosynthetic capacity and Rdark remained unchanged in cold-affiliated species, but the latter decreased in warm-affiliated counterparts. Rdark at 25°C increased with temperature in all species, but remained unchanged when expressed at Tg. Both species groups acclimated to temperature, but only warm-affiliated species decreased Rdark to photosynthetic capacity ratio at Tg as temperature increased. This could confer them a competitive advantage under future warming.
Abstract.
Author URL.
Ma Y, Yue X, Sitch S, Unger N, Uddling J, Mercado L, Gong C, Feng Z, Yang H, Zhou H, et al (2023). Implementation of trait-based ozone plant sensitivity in the Yale Interactive terrestrial Biosphere model v1.0 to assess global vegetation damage. GMD
Nagy L, Eller CB, Mercado LM, Cuesta FX, Llambí LD, Buscardo E, Aragão LEOC, García-Núñez C, Oliveira RS, Barbosa M, et al (2023). South American mountain ecosystems and global change – a case study for integrating theory and field observations for land surface modelling and ecosystem management. Plant Ecology & Diversity, ahead-of-print(ahead-of-print), 1-27.
2022
Bartholomew DC, Banin LF, Bittencourt PRL, Suis MAF, Mercado LM, Nilus R, Burslem DFRP, Rowland L (2022). Differential nutrient limitation and tree height control leaf physiology, supporting niche partitioning in tropical dipterocarp forests. Functional Ecology, 36(8), 2084-2103.
Cunha HFV, Andersen KM, Lugli LF, Santana FD, Aleixo IF, Moraes AM, Garcia S, Di Ponzio R, Mendoza EO, Brum B, et al (2022). Direct evidence for phosphorus limitation on Amazon forest productivity.
Nature,
608(7923), 558-562.
Abstract:
Direct evidence for phosphorus limitation on Amazon forest productivity.
The productivity of rainforests growing on highly weathered tropical soils is expected to be limited by phosphorus availability1. Yet, controlled fertilization experiments have been unable to demonstrate a dominant role for phosphorus in controlling tropical forest net primary productivity. Recent syntheses have demonstrated that responses to nitrogen addition are as large as to phosphorus2, and adaptations to low phosphorus availability appear to enable net primary productivity to be maintained across major soil phosphorus gradients3. Thus, the extent to which phosphorus availability limits tropical forest productivity is highly uncertain. The majority of the Amazonia, however, is characterized by soils that are more depleted in phosphorus than those in which most tropical fertilization experiments have taken place2. Thus, we established a phosphorus, nitrogen and base cation addition experiment in an old growth Amazon rainforest, with a low soil phosphorus content that is representative of approximately 60% of the Amazon basin. Here we show that net primary productivity increased exclusively with phosphorus addition. After 2 years, strong responses were observed in fine root (+29%) and canopy productivity (+19%), but not stem growth. The direct evidence of phosphorus limitation of net primary productivity suggests that phosphorus availability may restrict Amazon forest responses to CO2 fertilization4, with major implications for future carbon sequestration and forest resilience to climate change.
Abstract.
Author URL.
Farha MN, Daniells J, Cernusak LA, Ritmejerytė E, Wangchuk P, Sitch S, Mercado LM, Hayes F, Brown F, Cheesman AW, et al (2022). Examining Ozone Sensitivity in the Genus Musa (Bananas).
Rosan TM, Sitch S, Mercado LM, Heinrich V, Friedlingstein P, Aragão LEOC (2022). Fragmentation-Driven Divergent Trends in Burned Area in Amazonia and Cerrado. Frontiers in Forests and Global Change, 5
Hancock T (2022). How Does Plant Diversity Affect the Resilience of Forest Function to Disturbance in the Amazon Basin?.
Abstract:
How Does Plant Diversity Affect the Resilience of Forest Function to Disturbance in the Amazon Basin?
Dynamic global vegetation models (DGVMs) struggle to reproduce the spatial gradients of above-ground biomass (AGB) in Amazonia and the observed decline in the Amazonian carbon sink in recent years, making predictions for its future uncertain. This thesis focuses on two interconnected challenges in modelling Amazonian carbon dynamics: the lack of plant diversity in models using plant functional types (PFTs), and the unrealistic representation of mortality for tropical PFTs.
First, coexistence between PFTs is enabled in RED (Robust Ecosystem Demography), a cohort DGVM with Lotka competition dynamics. Inter-PFT competition, represented by a universal, variable competition coefficient (c), is assumed to be weaker than intra-PFT competition, contrary to assumptions in current models. This allows a tunable number of PFTs to coexist in a parameter sparse, and analytically solvable approach. Also presented is the idea of an optimum c, which maximises the Shannon diversity index per unit resource, replacing the need to quantify the strength of PFT interactions at the global scale. The optimum c value depends on the number of PFTs input and saturates at 0.8. The responses of vegetation carbon and growth rate to increased PFT coexistence are modelled at a point level to demonstrate the potential of the new competition scheme. It is shown that, in RED, PFT diversity increases forest function and impacts resilience by influencing the properties of the most growth-efficient PFT sampled. These results are important for modelling regions like Amazonia, where biodiversity is chronically underestimated in top-down DGVMs.
Spatially heterogeneous plant mortality rates are an important predictor of AGB patterns in Amazonia.
Therefore, in the second chapter, spatially variable mortality rates are enabled for the tropical tree PFT in TRIFFID, the DGVM currently coupled to the JULES land surface scheme, replacing a homogeneous mortality rate. Maps of Amazonian tree mortality are created using a well-known link with wood density and three independent wood density maps. Model outputs using the diversified mortality scheme, evaluated against observations of AGB, improve its representation in TRIFFID, mainly through a reduction in the model bias and an increase in the correlation with observed biomass.
Abstract.
Oliver RJ, Mercado LM, Clark DB, Huntingford C, Taylor CM, Vidale PL, McGuire PC, Todt M, Folwell S, Shamsudheen Semeena V, et al (2022). Improved representation of plant physiology in the. JULES-vn5.6 land surface model: photosynthesis. stomatal conductance and thermal acclimation.
Geoscientific Model Development,
15(14), 5567-5592.
Abstract:
Improved representation of plant physiology in the. JULES-vn5.6 land surface model: photosynthesis. stomatal conductance and thermal acclimation
Abstract. Carbon and water cycle dynamics of vegetation are controlled primarily by
photosynthesis and stomatal conductance (gs). Our goal is to improve the
representation of these key physiological processes within the JULES land
surface model, with a particular focus on refining the temperature
sensitivity of photosynthesis, impacting modelled carbon, energy and water
fluxes. We test (1) an implementation of the Farquhar et al. (1980) photosynthesis scheme and associated plant functional type-dependent
photosynthetic temperature response functions, (2) the optimality-based
gs scheme from Medlyn et al. (2011) and (3) the
Kattge and Knorr (2007) photosynthetic capacity thermal
acclimation scheme. New parameters for each model configuration are adopted
from recent large observational datasets that synthesise global experimental
data. These developments to JULES incorporate current physiological
understanding of vegetation behaviour into the model and enable users to
derive direct links between model parameters and ongoing measurement
campaigns that refine such parameter values. Replacement of the original
Collatz et al. (1991) C3 photosynthesis model with the Farquhar scheme
results in large changes in GPP for the current day, with ∼ 10 %
reduction in seasonal (June–August, JJA, and December–February, DJF) mean GPP
in tropical forests and ∼ 20 % increase in the northern
high-latitude forests in JJA. The optimality-based gs model decreases
the latent heat flux for the present day (∼ 10 %, with an
associated increase in sensible heat flux) across regions dominated by
needleleaf evergreen forest in the Northern Hemisphere summer. Thermal
acclimation of photosynthesis coupled with the Medlyn gs scheme reduced
tropical forest GPP by up to 5 % and increased GPP in the high-northern-latitude forests by between 2 % and 5 %. Evaluation of simulated carbon and
water fluxes by each model configuration against global data products shows
this latter configuration generates improvements in these key areas. Thermal
acclimation of photosynthesis coupled with the Medlyn gs scheme improved
modelled carbon fluxes in tropical and high-northern-latitude forests in
JJA and improved the simulation of evapotranspiration across much of the
Northern Hemisphere in JJA. Having established good model performance for
the contemporary period, we force this new version of JULES offline with a
future climate scenario corresponding to rising atmospheric greenhouse gases
(Shared Socioeconomic Pathway (SSP5), Representative Concentration Pathway 8.5 (RCP8.5)). In particular, these calculations allow for understanding of the effects of long-term warming. We find that the impact of thermal acclimation
coupled with the optimality-based gs model on simulated fluxes increases
latent heat flux (+50 %) by the year 2050 compared to the JULES model
configuration without acclimation. This new JULES configuration also
projects increased GPP across tropical (+10 %) and northern-latitude
regions (+30 %) by 2050. We conclude that thermal acclimation of
photosynthesis with the Farquhar photosynthesis scheme and the new
optimality-based gs scheme together improve the simulation of carbon and
water fluxes for the current day and have a large impact on modelled future
carbon cycle dynamics in a warming world.
.
Abstract.
Bruhn D, Newman F, Hancock M, Povlsen P, Slot M, Sitch S, Drake J, Weedon GP, Clark DB, Pagter M, et al (2022). Nocturnal plant respiration is under strong non-temperature control.
Nat Commun,
13(1).
Abstract:
Nocturnal plant respiration is under strong non-temperature control.
Most biological rates depend on the rate of respiration. Temperature variation is typically considered the main driver of daily plant respiration rates, assuming a constant daily respiration rate at a set temperature. Here, we show empirical data from 31 species from temperate and tropical biomes to demonstrate that the rate of plant respiration at a constant temperature decreases monotonically with time through the night, on average by 25% after 8 h of darkness. Temperature controls less than half of the total nocturnal variation in respiration. A new universal formulation is developed to model and understand nocturnal plant respiration, combining the nocturnal decrease in the rate of plant respiration at constant temperature with the decrease in plant respiration according to the temperature sensitivity. Application of the new formulation shows a global reduction of 4.5 -6 % in plant respiration and an increase of 7-10% in net primary production for the present-day.
Abstract.
Author URL.
Sarangi C, Tripathi S, Krishnan M, Morrison R, Evans J, Mercado LM (2022). Observations of aerosol–vapor pressure deficit–evaporative fraction coupling over India.
Atmospheric Chemistry and Physics,
22(5), 3615-3629.
Abstract:
Observations of aerosol–vapor pressure deficit–evaporative fraction coupling over India
Abstract. Northern India is a densely populated subtropical region with heavy aerosol
loading (mean aerosol optical depth or AOD is ∼0.7), frequent
heat waves, and strong atmosphere–biosphere coupling, making it ideal for
studying the impacts of aerosols and the temperature variation in latent heat flux (LH) and evaporative fraction (EF). Here, using in situ observations during the onset of the summer monsoon over a semi-natural grassland site in this region, we confirm that strong co-variability exists among aerosols, LH, air temperature (Tair), and the vapor pressure deficit (VPD). Since the surface evapotranspiration is strongly controlled by both physical (available energy and moisture demand) and physiological (canopy and aerodynamic resistance) factors, we separately analyze our data for different combinations of aerosols and Tair/VPD changes. We find that aerosol loading and warmer conditions both reduce sensible heat (SH). Furthermore, we find that an increase in atmospheric VPD tends to decrease the gross primary
production (GPP) and, thus, LH, most likely as a response to stomatal closure of the dominant grasses at this location. In contrast, under heavy aerosol loading, LH is enhanced partly due to the physiological control exerted by the diffuse radiation fertilization effect (thus increasing EF). Moreover, LH and EF increases with aerosol loading even under heat wave conditions, indicating a decoupling of the plant's response to the VPD enhancement (stomatal closure) in the presence of high aerosol conditions. Our results encourage detailed in situ experiments and mechanistic modeling of AOD–VPD–EF coupling for a better understanding of Indian monsoon dynamics and crop vulnerability in a heat stressed and heavily polluted future India.
.
Abstract.
Wu C, Sitch S, Huntingford C, Mercado LM, Venevsky S, Lasslop G, Archibald S, Staver AC (2022). Reduced global fire activity due to human demography slows global warming by enhanced land carbon uptake.
Proc Natl Acad Sci U S A,
119(20).
Abstract:
Reduced global fire activity due to human demography slows global warming by enhanced land carbon uptake.
Fire is an important climate-driven disturbance in terrestrial ecosystems, also modulated by human ignitions or fire suppression. Changes in fire emissions can feed back on the global carbon cycle, but whether the trajectories of changing fire activity will exacerbate or attenuate climate change is poorly understood. Here, we quantify fire dynamics under historical and future climate and human demography using a coupled global climate–fire–carbon cycle model that emulates 34 individual Earth system models (ESMs). Results are compared with counterfactual worlds, one with a constant preindustrial fire regime and another without fire. Although uncertainty in projected fire effects is large and depends on ESM, socioeconomic trajectory, and emissions scenario, we find that changes in human demography tend to suppress global fire activity, keeping more carbon within terrestrial ecosystems and attenuating warming. Globally, changes in fire have acted to warm climate throughout most of the 20th century. However, recent and predicted future reductions in fire activity may reverse this, enhancing land carbon uptake and corresponding to offsetting ∼5 to 10 y of global CO2 emissions at today’s levels. This potentially reduces warming by up to 0.11 °C by 2100. We show that climate–carbon cycle feedbacks, as caused by changing fire regimes, are most effective at slowing global warming under lower emission scenarios. Our study highlights that ignitions and active and passive fire suppression can be as important in driving future fire regimes as changes in climate, although with some risk of more extreme fires regionally and with implications for other ecosystem functions in fire-dependent ecosystems.
Abstract.
Author URL.
Wong CYS, Mercado LM, Arain MA, Ensminger I (2022). Remotely sensed carotenoid dynamics improve modelling photosynthetic phenology in conifer and deciduous forests.
Agricultural and Forest Meteorology,
321Abstract:
Remotely sensed carotenoid dynamics improve modelling photosynthetic phenology in conifer and deciduous forests
Detecting the phenology of photosynthesis, which conveys the length of the growing season, is key for terrestrial ecosystem models to constrain total annual carbon uptake and estimate gross primary productivity (GPP). However, some of the vegetation indices that are widely used for modelling GPP lack the ability to represent changes in the magnitude of photosynthesis, leading to errors in detecting phenology and large uncertainties. Crucially, remotely sensed vegetation indices such as the photochemical reflectance index (PRI) and chlorophyll/carotenoid index (CCI) can detect changes in foliar carotenoid composition that represent adjustments in photosynthetic light-use-efficiency (LUE) and changes in phenology. We modeled GPP from remote sensing data using PRI and CCI to represent foliar carotenoid changes as proxies for LUE. GPP values estimated from these PRI and CCI modified LUE models were compared against GPP from eddy covariance flux tower measurements, MODerate Resolution Imaging Spectroradiometer (MODIS) GPP product, conventional meteorological driven LUE-model, and process-based dynamic global vegetation model (ie. JULES) in an evergreen needleleaf and a deciduous broadleaf forest in the Great Lakes region. Overall, and in particular for evergreen needleleaf forests, estimates of start and end of growing season using PRI and CCI LUE-models showed less year-to-year variability than estimates obtained by process-based meteorological models. Although many process-based models provide reasonable estimates of start and end of growing season, our results demonstrate that using regulatory carotenoids and photosynthetic efficiency can improve remote monitoring of the phenology of forest vegetation.
Abstract.
Nakhavali MA, Mercado LM, Hartley IP, Sitch S, Cunha FV, di Ponzio R, Lugli LF, Quesada CA, Andersen KM, Chadburn SE, et al (2022). Representation of the phosphorus cycle in the Joint UK Land Environment Simulator (vn5.5_JULES-CNP).
Geoscientific Model Development,
15(13), 5241-5269.
Abstract:
Representation of the phosphorus cycle in the Joint UK Land Environment Simulator (vn5.5_JULES-CNP)
Abstract. Most land surface models (LSMs), i.e. the land components of Earth system models
(ESMs), include representation of nitrogen (N) limitation on ecosystem
productivity. However, only a few of these models have incorporated phosphorus
(P) cycling. In tropical ecosystems, this is likely to be important as N
tends to be abundant, whereas the availability of rock-derived elements, such as
P, can be very low. Thus, without a representation of P cycling, tropical
forest response in areas such as Amazonia to rising atmospheric CO2
conditions remain highly uncertain. In this study, we introduced P dynamics
and its interactions with the N and carbon (C) cycles into the Joint UK Land
Environment Simulator (JULES). The new model (JULES-CNP) includes the
representation of P stocks in vegetation and soil pools, as well as key
processes controlling fluxes between these pools. We develop and evaluate
JULES-CNP using in situ data collected at a low-fertility site in the
central Amazon, with a soil P content representative of 60 % of soils
across the Amazon basin, to parameterize, calibrate, and evaluate JULES-CNP.
Novel soil and plant P pool observations are used for parameterization and
calibration, and the model is evaluated against C fluxes and stocks and
those soil P pools not used for parameterization or calibration. We then
evaluate the model at additional P-limited test sites across the Amazon and in
Panama and Hawaii, showing a significant improvement over the C- and CN-only
versions of the model. The model is then applied under elevated
CO2 (600 ppm) at our study site in the central Amazon to quantify the impact
of P limitation on CO2 fertilization. We compare our results against the
current state-of-the-art CNP models using the same methodology that was used
in the AmazonFACE model intercomparison study. The model is able to
reproduce the observed plant and soil P pools and fluxes used for evaluation
under ambient CO2. We estimate P to limit net primary productivity
(NPP) by 24 % under current CO2 and by 46 % under elevated
CO2. Under elevated CO2, biomass in simulations accounting for CNP
increase by 10 % relative to contemporary CO2 conditions, although it
is 5 % lower compared to CN- and C-only simulations. Our results
highlight the potential for high P limitation and therefore lower CO2 fertilization capacity in the Amazon rainforest with low-fertility soils.
.
Abstract.
Brown F, Folberth GA, Sitch S, Bauer S, Bauters M, Boeckx P, Cheesman AW, Deushi M, Dos Santos I, Galy-Lacaux C, et al (2022). The ozone-climate penalty over South America and Africa by 2100.
ATMOSPHERIC CHEMISTRY AND PHYSICS,
22(18), 12331-12352.
Author URL.
Brown F, Folberth GA, Sitch S, Bauer S, Bauters M, Boeckx P, Cheesman AW, Deushi M, Dos Santos I, Galy-Lacaux C, et al (2022). The ozone–climate penalty over South America and Africa by 2100. , 2022, 1-33.
2021
Rosan TM, Klein Goldewijk K, Ganzenmüller R, O’Sullivan M, Pongratz J, Mercado LM, Aragao LEOC, Heinrich V, Von Randow C, Wiltshire A, et al (2021). A multi-data assessment of land use and land cover emissions from Brazil during 2000–2019.
Environmental Research Letters,
16(7), 074004-074004.
Abstract:
A multi-data assessment of land use and land cover emissions from Brazil during 2000–2019
Abstract
. Brazil is currently the largest contributor of land use and land cover change (LULCC) carbon dioxide net emissions worldwide, representing 17%–29% of the global total. There is, however, a lack of agreement among different methodologies on the magnitude and trends in LULCC emissions and their geographic distribution. Here we perform an evaluation of LULCC datasets for Brazil, including those used in the annual global carbon budget (GCB), and national Brazilian assessments over the period 2000–2018. Results show that the latest global HYDE 3.3 LULCC dataset, based on new FAO inventory estimates and multi-annual ESA CCI satellite-based land cover maps, can represent the observed spatial variation in LULCC over the last decades, representing an improvement on the HYDE 3.2 data previously used in GCB. However, the magnitude of LULCC assessed with HYDE 3.3 is lower than estimates based on MapBiomas. We use HYDE 3.3 and MapBiomas as input to a global bookkeeping model (bookkeeping of land use emission, BLUE) and a process-based Dynamic Global Vegetation Model (JULES-ES) to determine Brazil’s LULCC emissions over the period 2000–2019. Results show mean annual LULCC emissions of 0.1–0.4 PgC yr−1, compared with 0.1–0.24 PgC yr−1 reported by the Greenhouse Gas Emissions Estimation System of land use changes and forest sector (SEEG/LULUCF) and by FAO in its latest assessment of deforestation emissions in Brazil. Both JULES-ES and BLUE now simulate a slowdown in emissions after 2004 (−0.006 and −0.004 PgC yr−2 with HYDE 3.3, −0.014 and −0.016 PgC yr−2 with MapBiomas, respectively), in agreement with the Brazilian INPE-EM, global Houghton and Nassikas book-keeping models, FAO and as reported in the 4th national greenhouse gas inventories. The inclusion of Earth observation data has improved spatial representation of LULCC in HYDE and thus model capability to simulate Brazil’s LULCC emissions. This will likely contribute to reduce uncertainty in global LULCC emissions, and thus better constrains GCB assessments.
Abstract.
O’Sullivan M, Zhang Y, Bellouin N, Harris I, Mercado LM, Sitch S, Ciais P, Friedlingstein P (2021). Aerosol–light interactions reduce the carbon budget imbalance.
Environmental Research Letters,
16(12), 124072-124072.
Abstract:
Aerosol–light interactions reduce the carbon budget imbalance
Abstract
. Current estimates of the global land carbon sink contain substantial uncertainties on interannual timescales which contribute to a non-closure in the global carbon budget (GCB) in any given year. This budget imbalance (BIM) partly arises due to the use of imperfect models which are missing or misrepresenting processes. One such omission is the separate treatment of downward direct and diffuse solar radiation on photosynthesis. Here we evaluate and use an improved high-resolution (6-hourly), gridded dataset of surface solar diffuse and direct fluxes, over 1901–2017, constrained by satellite and ground-level observations, to drive two global land models. Results show that tropospheric aerosol–light interactions have the potential for substantial land carbon impacts (up to 0.4 PgCyr-1 enhanced sink) at decadal timescales, however large uncertainties remain, with models disagreeing on the direction of change in carbon uptake. On interannual timescales, results also show an enhancement of the land carbon sink (up to 0.9 PgCyr-1) and subsequent reduction in BIM by 55% in years following volcanic eruptions. We therefore suggest GCB assessments include this dataset in order to improve land carbon sink estimates.
Abstract.
Wu C, Venevsky S, Sitch S, Mercado LM, Huntingford C, Staver AC (2021). Historical and future global burned area with changing climate and human demography.
One Earth,
4(4), 517-530.
Abstract:
Historical and future global burned area with changing climate and human demography
Wildfires influence terrestrial carbon cycling and represent a safety risk, and yet a process-based understanding of their frequency and spatial distributions remains elusive. We combine satellite-based observations with an enhanced dynamic global vegetation model to make regionally resolved global assessments of burned area (BA) responses to changing climate, derived from 34 Earth system models and human demographics for 1860–2100. Limited by climate and socioeconomics, recent BA has decreased, especially in central South America and mesic African savannas. However, future simulations predict increasing BA due to changing climate, rapid population density growth, and urbanization. BA increases are especially notable at high latitudes, due to accelerated warming, and over the tropics and subtropics, due to drying and human ignitions. Conversely, rapid urbanization also limits BA via enhanced fire suppression in the immediate vicinity of settlements, offsetting the potential for dramatic future increases, depending on warming extent. Our analysis provides further insight into regional and global BA trends, highlighting the importance of including human demographic change in models for wildfire under changing climate.
Abstract.
Lugli LF, Rosa JS, Andersen KM, Di Ponzio R, Almeida RV, Pires M, Cordeiro AL, Cunha HFV, Martins NP, Assis RL, et al (2021). Rapid responses of root traits and productivity to phosphorus and cation additions in a tropical lowland forest in Amazonia.
New Phytol,
230(1), 116-128.
Abstract:
Rapid responses of root traits and productivity to phosphorus and cation additions in a tropical lowland forest in Amazonia.
Soil nutrient availability can strongly affect root traits. In tropical forests, phosphorus (P) is often considered the main limiting nutrient for plants. However, support for the P paradigm is limited, and N and cations might also control tropical forests functioning. We used a large-scale experiment to determine how the factorial addition of nitrogen (N), P and cations affected root productivity and traits related to nutrient acquisition strategies (morphological traits, phosphatase activity, arbuscular mycorrhizal colonisation and nutrient contents) in a primary rainforest growing on low-fertility soils in Central Amazonia after 1 yr of fertilisation. Multiple root traits and productivity were affected. Phosphorus additions increased annual root productivity and root diameter, but decreased root phosphatase activity. Cation additions increased root productivity at certain times of year, also increasing root diameter and mycorrhizal colonisation. P and cation additions increased their element concentrations in root tissues. No responses were detected with N addition. Here we showed that rock-derived nutrients determined root functioning in low-fertility Amazonian soils, demonstrating not only the hypothesised importance of P, but also highlighting the role of cations. The changes in fine root traits and productivity indicated that even slow-growing tropical rainforests can respond rapidly to changes in resource availability.
Abstract.
Author URL.
Nakhavali MA, Mercado L, Hartley IP, Sitch S, Cunha FV, Ponzio RD, Lugli LF, Quesada CA, Andersen KM, Chadburn SE, et al (2021). Representation of phosphorus cycle in Joint UK Land Environment Simulator (vn5.5_JULES-CNP).
Geoscientific Model Development DiscussionsAbstract:
Representation of phosphorus cycle in Joint UK Land Environment Simulator (vn5.5_JULES-CNP)
Most Land Surface Models (LSMs), the land components of Earth system models (ESMs), include representation of N limitation on ecosystem productivity. However only few of these models have incorporated phosphorus (P) cycling. In tropical ecosystems, this is likely to be particularly important as N tends to be abundant but the availability of rock-derived elements, such as P, can be very low. Thus, without a representation of P cycling, tropical forest response in areas such as Amazonia to rising atmospheric CO2 conditions remains highly uncertain. In this study, we introduced P dynamics and its interactions with the N and carbon (C) cycles into the Joint UK Land Environment Simulator (JULES). The new model (JULES-CNP) includes the representation of P stocks in vegetation and soil pools, as well as key processes controlling fluxes between these pools. We evaluate JULES-CNP at the Amazon nutrient fertilization experiment (AFEX), a low fertility site, representative of about 60 % of Amazon soils. We apply the model under ambient CO2 and elevated CO2. The model is able to reproduce the observed plant and soil P pools and fluxes under ambient CO2. We estimate P to limit net primary productivity (NPP) by 24 % under current CO2 and by 46 % under elevated CO2. Under elevated CO2, biomass in simulations accounting for CNP increase by 10 % relative to at contemporary CO2, although it is 5 % lower compared with CN and C-only simulations. Our results highlight the potential for high P limitation and therefore lower CO2 fertilization capacity in the Amazon forest with low fertility soils.
Abstract.
Bartholomew D (2021). Tree Function and Habitat Niche Partitioning in Tropical Forests:
Implications for Responses to Environmental Change.
Abstract:
Tree Function and Habitat Niche Partitioning in Tropical Forests:
Implications for Responses to Environmental Change
Tropical forests possess exceptional levels of tree species richness but explaining this diversity has presented a long existing challenge. Habitat niche partitioning provides a hypothesis for species co-existence, whereby species avoid competitive exclusion by partitioning demands on multiple resources within an environment. However, limited understanding concerning how tree function is influenced by multiple environmental variables has limited the support for this hypothesis. This knowledge gap also limits our ability to predict how tropical forest tree communities will respond to environmental change, given multiple dimensions of a species’ niche are likely to be affected.
In this thesis, I investigate the role of niche partitioning in supporting co-existence of species and the turnover of species across edaphic gradients, as well as how long-term changes to the environment from selective logging and drought affect niche space of tropical tree species. I use species distribution models and measurements of leaf physiological traits to determine the key dimensions of tree species’ niches in primary forests.
In chapter 2 I demonstrate niche partitioning is strong within tropical forests with at least 60-86% of abundant species occupying their own unique niche. Species partition a wide range of abiotic environments, including soil nutrient, topographic and light environments, with greater environmental heterogeneity enhancing the scope for niche partitioning. Building on this, in chapter 3 I find that variation in nutrient availability explains more variation in leaf physiology and habitat preferences than light availability of species from the Dipterocarpaceae family that dominates South-East Asian forests. This highlights the importance of edaphic environments in structuring tropical forest communities. I also find different leaf nutrients are related to photosynthetic capacity in different forest types, revealing that multiple different nutrients may limit productivity and affect species distributions in tropical forests.
Many tropical forest tree species are highly specialised with limited ability to adjust their traits between environments, underlining their potential vulnerability to environmental change. In chapter 4 I show seedlings from selectively logged Bornean forests have different community weighted mean trait values, with greater belowground investment in logged forests. These adaptations are sufficient to overcome soil stress and to maintain foliar nutrient concentrations. However, I show seedlings of species that dominate old-growth forests are less able to adapt their traits and experience elevated mortality rates in logged forests. I attribute this to greater soil nutrient limitation as they are unable to maintain leaf nutrient concentrations. Selective logging will therefore likely drive shifts in species composition towards greater dominance of earlier-successional species that have traits capable of surviving in disturbed environments. This could result in local-scale reductions in species diversity and functional diversity, which could reduce long-term resilience to environmental change. In contrast, in Chapter 5 I demonstrate small trees in Amazonian forests are able to respond to changes in their environment following long-term drought conditions. Following mortality of large canopy trees, small trees can respond to increased light availability even under reduced water availability by adjusting resource allocation and by increasing nutrient use efficiency. Despite evidence of resilience to long-term drought conditions, hyper-dominant species show a greater capacity to respond, which may further enhance the dominance of these species under future climates.
In conclusion my results highlight the importance of habitat niche partitioning in structuring tropical forest tree communities and identify key environmental variables that determine species distribution and tree function. My results have important implications for the conservation and restoration of tropical forests under environmental change. Avoidance of environmental homogenisation and changes to as few environmental conditions as possible is likely to be important in maintaining high species diversity in tropical forests and to avoid increased dominance by few generalist species. Many current conservation and restoration projects focus on recovering vegetation, but my research highlights the additional need to maintain and restore soil environments, especially for the long-term persistence of highly specialist species.
Abstract.
Restrepo-Coupe N, Albert LP, Longo M, Baker I, Levine NM, Mercado LM, da Araujo AC, Christoffersen BO, Costa MH, Fitzjarrald DR, et al (2021). Understanding water and energy fluxes in the Amazonia: Lessons from an observation-model intercomparison.
Glob Chang Biol,
27(9), 1802-1819.
Abstract:
Understanding water and energy fluxes in the Amazonia: Lessons from an observation-model intercomparison.
Tropical forests are an important part of global water and energy cycles, but the mechanisms that drive seasonality of their land-atmosphere exchanges have proven challenging to capture in models. Here, we (1) report the seasonality of fluxes of latent heat (LE), sensible heat (H), and outgoing short and longwave radiation at four diverse tropical forest sites across Amazonia-along the equator from the Caxiuanã and Tapajós National Forests in the eastern Amazon to a forest near Manaus, and from the equatorial zone to the southern forest in Reserva Jaru; (2) investigate how vegetation and climate influence these fluxes; and (3) evaluate land surface model performance by comparing simulations to observations. We found that previously identified failure of models to capture observed dry-season increases in evapotranspiration (ET) was associated with model overestimations of (1) magnitude and seasonality of Bowen ratios (relative to aseasonal observations in which sensible was only 20%-30% of the latent heat flux) indicating model exaggerated water limitation, (2) canopy emissivity and reflectance (albedo was only 10%-15% of incoming solar radiation, compared to 0.15%-0.22% simulated), and (3) vegetation temperatures (due to underestimation of dry-season ET and associated cooling). These partially compensating model-observation discrepancies (e.g. higher temperatures expected from excess Bowen ratios were partially ameliorated by brighter leaves and more interception/evaporation) significantly biased seasonal model estimates of net radiation (Rn ), the key driver of water and energy fluxes (LE ~ 0.6 Rn and H ~ 0.15 Rn ), though these biases varied among sites and models. A better representation of energy-related parameters associated with dynamic phenology (e.g. leaf optical properties, canopy interception, and skin temperature) could improve simulations and benchmarking of current vegetation-atmosphere exchange and reduce uncertainty of regional and global biogeochemical models.
Abstract.
Author URL.
2020
Newman F (2020). Quantifying the temperature independent controls of nocturnal plant respiration.
Abstract:
Quantifying the temperature independent controls of nocturnal plant respiration
Autotrophic respiration is a critical determinant of plant, ecosystem and global carbon exchange, constituting a major control on the evolution of the contemporary carbon cycle with the potential to modulate the magnitude of future climate change. Due to an incomplete understanding of plant respiration and its underlying mechanisms, the process remains an important yet poorly quantified component of the global carbon cycle and currently dominates uncertainties in carbon cycle modelling. Plant respiration is currently represented by a fixed exponential temperature function in vegetation and earth system models. This rather simplistic description is inadequate to describe the co-regulation of respiration by endogenous mechanisms over longer timescales, such as the control exerted by substrate supply, product demand and the circadian clock. This study compiles the first comprehensive dataset of nocturnal leaf respiration to explore and quantify the temperature-independent control of leaf respiratory metabolism at night. A down-regulation in nocturnal respiration was observed to occur under constant temperature conditions which decreased the basal rate of respiration by ~40% of the initial rate at the onset of darkness, indicating the base rate of respiration cannot be considered constant as generally assumed in all modern field studies and models. An empirically derived term representing the non-temperature dependent component of leaf respiration at night was applied to the land surface component of an earth system model to describe nocturnal variation in endogenous metabolism in addition to the temperature dependency of respiration. Accounting for the non-temperature dependency of nocturnal respiration reduced annual rates of modelled plant respiration by up to 10% and increased annual net primary productivity by up to 16% across all tropical and temperate forest sites, suggesting that previous models have overestimated global respiration and underestimated net primary productivity, particularly in the tropics. The significant impact of the novel term presents important implications for land-atmosphere studies and estimates of global terrestrial carbon balance and storage. This study provides the foundation from which to advance research on endogenous rhythms in plant metabolism to develop a more comprehensive understanding and description of plant respiration for modelling frameworks, ultimately to increase the realism of vegetation models for greater confidence in simulations of the current and future terrestrial and global carbon cycle.
Abstract.
Bartholomew DC, Bittencourt PRL, da Costa ACL, Banin LF, de Britto Costa P, Coughlin SI, Domingues TF, Ferreira LV, Giles A, Mencuccini M, et al (2020). Small tropical forest trees have a greater capacity to adjust carbon metabolism to long-term drought than large canopy trees.
Plant Cell Environ,
43(10), 2380-2393.
Abstract:
Small tropical forest trees have a greater capacity to adjust carbon metabolism to long-term drought than large canopy trees.
The response of small understory trees to long-term drought is vital in determining the future composition, carbon stocks and dynamics of tropical forests. Long-term drought is, however, also likely to expose understory trees to increased light availability driven by drought-induced mortality. Relatively little is known about the potential for understory trees to adjust their physiology to both decreasing water and increasing light availability. We analysed data on maximum photosynthetic capacity (Jmax , Vcmax ), leaf respiration (Rleaf ), leaf mass per area (LMA), leaf thickness and leaf nitrogen and phosphorus concentrations from 66 small trees across 12 common genera at the world's longest running tropical rainfall exclusion experiment and compared responses to those from 61 surviving canopy trees. Small trees increased Jmax , Vcmax , Rleaf and LMA (71, 29, 32, 15% respectively) in response to the drought treatment, but leaf thickness and leaf nutrient concentrations did not change. Small trees were significantly more responsive than large canopy trees to the drought treatment, suggesting greater phenotypic plasticity and resilience to prolonged drought, although differences among taxa were observed. Our results highlight that small tropical trees have greater capacity to respond to ecosystem level changes and have the potential to regenerate resilient forests following future droughts.
Abstract.
Author URL.
2019
Kumarathunge DP, Medlyn BE, Drake JE, Tjoelker MG, Aspinwall MJ, Battaglia M, Cano FJ, Carter KR, Cavaleri MA, Cernusak LA, et al (2019). Acclimation and adaptation components of the temperature dependence of plant photosynthesis at the global scale.
New Phytologist,
222(2), 768-784.
Abstract:
Acclimation and adaptation components of the temperature dependence of plant photosynthesis at the global scale
The temperature response of photosynthesis is one of the key factors determining predicted responses to warming in global vegetation models (GVMs). The response may vary geographically, owing to genetic adaptation to climate, and temporally, as a result of acclimation to changes in ambient temperature. Our goal was to develop a robust quantitative global model representing acclimation and adaptation of photosynthetic temperature responses. We quantified and modelled key mechanisms responsible for photosynthetic temperature acclimation and adaptation using a global dataset of photosynthetic CO 2 response curves, including data from 141 C 3 species from tropical rainforest to Arctic tundra. We separated temperature acclimation and adaptation processes by considering seasonal and common-garden datasets, respectively. The observed global variation in the temperature optimum of photosynthesis was primarily explained by biochemical limitations to photosynthesis, rather than stomatal conductance or respiration. We found acclimation to growth temperature to be a stronger driver of this variation than adaptation to temperature at climate of origin. We developed a summary model to represent photosynthetic temperature responses and showed that it predicted the observed global variation in optimal temperatures with high accuracy. This novel algorithm should enable improved prediction of the function of global ecosystems in a warming climate.
Abstract.
Fleischer K, Rammig A, De Kauwe MG, Walker AP, Domingues TF, Fuchslueger L, Garcia S, Goll DS, Grandis A, Jiang M, et al (2019). Amazon forest response to CO<inf>2</inf> fertilization dependent on plant phosphorus acquisition.
Nature Geoscience,
12(9), 736-741.
Abstract:
Amazon forest response to CO2 fertilization dependent on plant phosphorus acquisition
Global terrestrial models currently predict that the Amazon rainforest will continue to act as a carbon sink in the future, primarily owing to the rising atmospheric carbon dioxide (CO2) concentration. Soil phosphorus impoverishment in parts of the Amazon basin largely controls its functioning, but the role of phosphorus availability has not been considered in global model ensembles—for example, during the Fifth Climate Model Intercomparison Project. Here we simulate the planned free-air CO2 enrichment experiment AmazonFACE with an ensemble of 14 terrestrial ecosystem models. We show that phosphorus availability reduces the projected CO2-induced biomass carbon growth by about 50% to 79 ± 63 g C m−2 yr−1 over 15 years compared to estimates from carbon and carbon–nitrogen models. Our results suggest that the resilience of the region to climate change may be much less than previously assumed. Variation in the biomass carbon response among the phosphorus-enabled models is considerable, ranging from 5 to 140 g C m−2 yr−1, owing to the contrasting plant phosphorus use and acquisition strategies considered among the models. The Amazon forest response thus depends on the interactions and relative contributions of the phosphorus acquisition and use strategies across individuals, and to what extent these processes can be upregulated under elevated CO2.
Abstract.
Yang H, Huntingford C, Wiltshire A, Sitch S, Mercado L (2019). Compensatory climate effects link trends in global runoff to rising atmospheric CO2 concentration.
ENVIRONMENTAL RESEARCH LETTERS,
14(12).
Author URL.
Figueiredo Lugli L (2019). Dynamics and biological interactions of phosphorus cycling in central Amazonian forests.
Abstract:
Dynamics and biological interactions of phosphorus cycling in central Amazonian forests
Soil nutrient availability is considered to constrain the productivity of terrestrial ecosystems, with phosphorus (P) considered to be the most limiting nutrient in tropical forests. Due the great importance of Amazon forests in carbon (C) cycling and the fact that the majority of Amazon forests grow in low-fertility soils, understanding how nutrient limitation may affect net primary productivity (NPP) in these ecosystems is crucial to predict C storage in response to future climate. The direct effects of nutrient limitation on above and belowground forest functioning can only be tested through experimentation and up to now, the few large scale fertilisation experiments installed in lowland tropical forests indicate that multiple nutrients may limit different aspects of tropical forests, with inconsistent evidence for P limitation. Since much less is known about the potential effects of nutrient limitation on belowground forest functioning, this research aimed to analyse the main belowground mechanisms involved in P cycling, and how roots and soil microorganisms adapt to different conditions of soil fertility in central Amazon forests. I investigated how root morphological traits, mycorrhizal colonisation as well as enzyme exudation both from roots and soil microbes were expressed in natural low-fertility soils and how these traits responded to the short-term addition of P, nitrogen (N) and cations, as part of the first large-scale soil nutrient manipulation experiment in a central Amazon lowland forest near Manaus, Brazil. I show that in natural low-fertility soils, roots display a range of adaptations to increase P-uptake efficiency and investments in root morphological and physiological adaptations as well as association with fungi symbionts are complementary towards maintaining forest productivity in a central Amazon forest. With nutrient addition, I found support for the hypothesis of P-limitation, since trees were able to rapidly adapt their root morphological traits, reduce investments in enzyme exudation and increase association with mycorrhizal fungi. Such responses were also affected by cation addition, reinforcing the idea that multiple nutrients may control the expression of root traits. The soil microbial community was also affected by the short-term addition of nutrients, with a reduction in enzyme production with the addition of phosphorus, indicating a rapid alleviation of phosphorus limitation, but this reduction was eliminated when cations were also added. My results suggest that plants and soil microorganisms can rapidly respond to changes in soil nutrient
Abstract
4
availability by changing their investments in nutrient uptake mechanisms, ultimately impacting plant productivity. These responses are crucial if we are to better understand how these forests function and how they may respond to global change.
Abstract.
Williams KE, Harper AB, Huntingford C, Mercado LM, Mathison CT, Falloon PD, Cox PM, Kim J (2019). How can the First ISLSCP Field Experiment contribute to present-day efforts to evaluate water stress in JULESv5.0?.
Geoscientific Model Development,
12(7), 3207-3240.
Abstract:
How can the First ISLSCP Field Experiment contribute to present-day efforts to evaluate water stress in JULESv5.0?
The First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE), Kansas, US, 1987-1989, made important contributions to the understanding of energy and CO2 exchanges between the land surface and the atmosphere, which heavily influenced the development of numerical land-surface modelling. Now, 30 years on, we demonstrate how the wealth of data collected during FIFE and its subsequent in-depth analysis in the literature continue to be a valuable resource for the current generation of land-surface models. To illustrate, we use the FIFE dataset to evaluate the representation of water stress on tallgrass prairie vegetation in the Joint UK Land Environment Simulator (JULES) and highlight areas for future development. We show that, while JULES is able to simulate a decrease in net carbon assimilation and evapotranspiration during a dry spell, the shape of the diurnal cycle is not well captured. Evaluating the model parameters and results against this dataset provides a case study on the assumptions in calibrating "unstressed" vegetation parameters and thresholds for water stress. In particular, the responses to low water availability and high temperatures are calibrated separately. We also illustrate the effect of inherent uncertainties in key observables, such as leaf area index, soil moisture and soil properties. Given these valuable lessons, simulations for this site will be a key addition to a compilation of simulations covering a wide range of vegetation types and climate regimes, which will be used to improve the way that water stress is represented within JULES.
Abstract.
Rap A, Scott CE, Reddington CL, Mercado L, Ellis RJ, Garraway S, Evans MJ, Beerling DJ, MacKenzie AR, Hewitt CN, et al (2019). Reply to: Complexities between plants and the atmosphere. Nature Geoscience, 12(9), 695-695.
Malavelle FF, Haywood JM, Mercado LM, Folberth GA, Bellouin N, Sitch S, Artaxo P (2019). Studying the impact of biomass burning aerosol radiative and climate effects on the Amazon rainforest productivity with an Earth system model.
Atmospheric Chemistry and Physics,
19(2), 1301-1326.
Abstract:
Studying the impact of biomass burning aerosol radiative and climate effects on the Amazon rainforest productivity with an Earth system model
Diffuse light conditions can increase the efficiency of photosynthesis and carbon uptake by vegetation canopies. The diffuse fraction of photosynthetically active radiation (PAR) can be affected by either a change in the atmospheric aerosol burden and/or a change in cloudiness. During the dry season, a hotspot of biomass burning on the edges of the Amazon rainforest emits a complex mixture of aerosols and their precursors and climate-active trace gases (e.g. CO 2 , CH 4 , NO x ). This creates potential for significant interactions between chemistry, aerosol, cloud, radiation and the biosphere across the Amazon region. The combined effects of biomass burning on the terrestrial carbon cycle for the present day are potentially large, yet poorly quantified. Here, we quantify such effects using the Met Office Hadley Centre Earth system model HadGEM2-ES, which provides a fully coupled framework with interactive aerosol, radiative transfer, dynamic vegetation, atmospheric chemistry and biogenic volatile organic compound emission components. Results show that for present day, defined as year 2000 climate, the overall net impact of biomass burning aerosols is to increase net primary productivity (NPP) by +80 to +105 TgC yr -1 , or 1.9% to 2.7 %, over the central Amazon Basin on annual mean. For the first time we show that this enhancement is the net result of multiple competing effects: an increase in diffuse light which stimulates photosynthetic activity in the shaded part of the canopy (+65 to +110 TgC yr -1 ), a reduction in the total amount of radiation (-52 to -1 05 TgC yr -1 ) which reduces photosynthesis and feedback from climate adjustments in response to the aerosol forcing which increases the efficiency of biochemical processes (+67 to +100 TgC yr -1 ). These results illustrate that despite a modest direct aerosol effect (the sum of the first two counteracting mechanisms), the overall net impact of biomass burning aerosols on vegetation is sizeable when indirect climate feedbacks are considered. We demonstrate that capturing the net impact of aerosols on vegetation should be assessed considering the system-wide behaviour.
Abstract.
Harrison ME, Ottay JB, D’Arcy LJ, Cheyne SM, Anggodo, Belcher C, Cole L, Dohong A, Ermiasi Y, Feldpausch T, et al (2019). Tropical forest and peatland conservation in Indonesia: Challenges and directions. People and Nature, 2(1), 4-28.
Wu C (2019). Wildfire modelling and impacts on carbon cycle, climate, and vegetation distribution induced by climate change.
Abstract:
Wildfire modelling and impacts on carbon cycle, climate, and vegetation distribution induced by climate change
Wildfire is a natural and unavoidable feature of the environment in many terrestrial ecosystems and has a strong influence on global ecosystem patterns and processes, including vegetation distribution and structure, the carbon cycle, and climate. However, as illustrated in recent studies, fire is a risk to human societies, emits atmospheric pollutants, and causes death and damage to homes and businesses. Fire regimes have been altered by complex interactions among climate change, anthropogenic activities, and biome community changes and are predicted to change further with global warming, population growth, and urbanization. Therefore, the frequency and spatial distribution of wildfires, along with their drivers of recent trends, requires better understanding to enable robust future predictions. Many studies have had a central focus on the interactions between the carbon cycle and climate. However, as an important component in modulating future climate change, the climate-carbon feedback derived from changing fires is poorly understood.
Here, we develop a fully coupled climate-vegetation-carbon-fire framework and perform simulations to investigate global Burnt Area (BA) trends and their drivers, climate-carbon feedbacks derived from changing fires, and the role of fire on the global carbon cycle. Meanwhile, the individual contribution of fire and climate on regional vegetation distribution is assessed using models, remote sensing technology and statistics.
The main results and conclusions are provided below:
(1) Global BA has decreased, and this is reproduced well in our simulation framework, capturing recent climate and human limits of change. Global BA will increase under climate change, rapid population growth and urbanization, and this is especially through high latitude warming and increases in human-induced fires over the tropics and subtropics. However, urbanization will also offset the potential future large increases in BA by enhancing fire suppression capacities and management.
(2) over the period 2005-2014, the carbon-cycle effect (i.e. caused via release of extra carbon into the atmosphere) of fire has increased the additional mean annual global land temperature by ~0.16 °C yr-1 relative to a world without fires. Future mean annual global fire carbon emissions will be sensitive to anthropogenic CO2 emissions and human behaviour (2.2 to 3.0 PgC yr-1), providing an approximate increasing mean annual atmospheric CO2 concentration of 15-22 ppm yr-1 and global land-mean warming of 0.13 to 0.18 °C yr-1 over the period 2081-2100, with warming being greatest at high latitudes. However, although the largest impact of fire on atmospheric CO2 concentrations is associated with the more severe anthropogenic emissions scenarios, the associated fire-climate feedbacks on enhanced warming are the lowest under these scenarios.
(3) the vegetation distribution for the present day is mainly determined directly by climate (35%) rather than fire (1%-10.9%). However, global warming will change the balance between fire and climate in driving variations of boreal forest distribution under four global warming scenarios. With a future global warming of 1.5 °C, the fire control on local vegetation composition will grow to exceed that of climate (36.3% > 29.3%). Above a 1.5 °C warming, temperature will be more important than fires in regulating vegetation distribution, although other factors like precipitation will also contribute.
Our analysis will help to develop wildfire management strategies in conditions of different possible future socioeconomic development pathways, to assess future ecological changes, and to help inform adaptation and mitigation options to global climate change.
Abstract.
2018
Zelazowski P, Huntingford C, Mercado LM, Schaller N (2018). Climate pattern-scaling set for an ensemble of 22 GCMs - adding uncertainty to the IMOGEN version 2.0 impact system.
GEOSCIENTIFIC MODEL DEVELOPMENT,
11(2), 541-560.
Author URL.
Rap A, Scott CE, Reddington CL, Mercado L, Ellis RJ, Garraway S, Evans MJ, Beerling DJ, MacKenzie AR, Hewitt CN, et al (2018). Enhanced global primary production by biogenic aerosol via diffuse radiation fertilization.
Nature Geoscience,
11(9), 640-644.
Abstract:
Enhanced global primary production by biogenic aerosol via diffuse radiation fertilization
Terrestrial vegetation releases large quantities of plant volatiles into the atmosphere that can then oxidize to form secondary organic aerosol. These particles affect plant productivity through the diffuse radiation fertilization effect by altering the balance between direct and diffuse radiation reaching the Earth’s surface. Here, using a suite of models describing relevant coupled components of the Earth system, we quantify the impacts of biogenic secondary organic aerosol on plant photosynthesis through this fertilization effect. We show that this leads to a net primary productivity enhancement of 1.23 Pg C yr−1 (range 0.76–1.61 Pg C yr−1 due to uncertainty in biogenic secondary organic aerosol formation). Notably, this productivity enhancement is twice the mass of biogenic volatile organic compound emissions (and ~30 times larger than the mass of carbon in biogenic secondary organic aerosol) causing it. Hence, our simulations indicate that there is a strong positive ecosystem feedback between biogenic volatile organic compound emissions and plant productivity through plant-canopy light-use efficiency. We estimate a gain of 1.07 in global biogenic volatile organic compound emissions resulting from this feedback.
Abstract.
Oliver RJ, Mercado LM, Sitch S, Simpson D, Medlyn BE, Lin Y-S, Folberth GA (2018). Large but decreasing effect of ozone on the European carbon sink.
BIOGEOSCIENCES,
15(13), 4245-4269.
Author URL.
Huntingford C, Oliver RJ, Mercado LM, Sitch S (2018). Technical note: a simple theoretical model framework to describe plant stomatal "sluggishness" in response to elevated ozone concentrations.
Biogeosciences,
15(17), 5415-5422.
Abstract:
Technical note: a simple theoretical model framework to describe plant stomatal "sluggishness" in response to elevated ozone concentrations
Elevated levels of tropospheric ozone, O3, cause damage to terrestrial vegetation, affecting leaf stomatal functioning and reducing photosynthesis. Climatic impacts under future raised atmospheric greenhouse gas (GHG) concentrations will also impact on the net primary productivity (NPP) of vegetation, which might for instance alter viability of some crops. Together, ozone damage and climate change may adjust the current ability of terrestrial vegetation to offset a significant fraction of carbon dioxide (CO2) emissions. Climate impacts on the land surface are well studied, but arguably large-scale modelling of raised surface level O3 effects is less advanced. To date most models representing ozone damage use either O3 concentration or, more recently, flux-uptake-related reduction of stomatal opening, estimating suppressed land-atmosphere water and CO2 fluxes. However there is evidence that, for some species, O3 damage can also cause an inertial sluggishness of stomatal response to changing surface meteorological conditions. In some circumstances (e.g. droughts), this loss of stomata control can cause them to be more open than without ozone interference. To both aid model development and provide empiricists with a system on to which measurements can be mapped, we present a parameter-sparse framework specifically designed to capture sluggishness. This contains a single time-delay parameter τO3, characterizing the timescale for stomata to catch up with the level of opening they would have without damage. The larger the value of this parameter, the more sluggish the modelled stomatal response. Through variation of τO3, we find it is possible to have qualitatively similar responses to factorial experiments with and without raised O3, when comparing to reported measurement time series presented in the literature. This low-parameter approach lends itself to the inclusion of ozone-induced inertial effects being incorporated in the terrestrial vegetation component of Earth system models (ESMs).
Abstract.
Salazar A, Sanchez A, Villegas JC, Salazar JF, Ruiz Carrascal D, Sitch S, Restrepo JD, Poveda G, Feeley KJ, Mercado LM, et al (2018). The ecology of peace: preparing Colombia for new political and planetary climates.
Frontiers in Ecology and the Environment,
16(9), 525-531.
Abstract:
The ecology of peace: preparing Colombia for new political and planetary climates
Colombia, one of the world's most species-rich nations, is currently undergoing a profound social transition: the end of a decades-long conflict with the Revolutionary Armed Forces of Colombia, known as FARC. The peace agreement process will likely transform the country's physical and socioeconomic landscapes at a time when humans are altering Earth's atmosphere and climate in unprecedented ways. We discuss ways in which these transformative events will act in combination to shape the ecological and environmental future of Colombia. We also highlight the risks of creating perverse development incentives in these critical times, along with the potential benefits – for the country and the world – if Colombia can navigate through the peace process in a way that protects its own environment and ecosystems.
Abstract.
Harper AB, Wiltshire AJ, Cox PM, Friedlingstein P, Jones CD, Mercado LM, Sitch S, Williams K, Duran-Rojas C (2018). Vegetation distribution and terrestrial carbon cycle in a carbon cycle configuration of JULES4.6 with new plant functional types.
Geoscientific Model Development,
11(7), 2857-2873.
Abstract:
Vegetation distribution and terrestrial carbon cycle in a carbon cycle configuration of JULES4.6 with new plant functional types
Dynamic global vegetation models (DGVMs) are used for studying historical and future changes to vegetation and the terrestrial carbon cycle. JULES (the Joint UK Land Environment Simulator) represents the land surface in the Hadley Centre climate models and in the UK Earth System Model. Recently the number of plant functional types (PFTs) in JULES was expanded from five to nine to better represent functional diversity in global ecosystems. Here we introduce a more mechanistic representation of vegetation dynamics in TRIFFID, the dynamic vegetation component of JULES, which allows for any number of PFTs to compete based solely on their height; therefore, the previous hardwired dominance hierarchy is removed. With the new set of nine PFTs, JULES is able to more accurately reproduce global vegetation distribution compared to the former five PFT version. Improvements include the coverage of trees within tropical and boreal forests and a reduction in shrubs, the latter of which dominated at high latitudes. We show that JULES is able to realistically represent several aspects of the global carbon (C) cycle. The simulated gross primary productivity (GPP) is within the range of observations, but simulated net primary productivity (NPP) is slightly too high. GPP in JULES from 1982 to 2011 is 133PgCyrg'1, compared to observation-based estimates (over the same time period) between 1238 and 150-175PgCyrg'1. NPP from 2000 to 2013 is 72PgCyrg'1, compared to satellite-derived NPP of 55PgCyrg'1 over the same period and independent estimates of 56.214.3PgCyrg'1. The simulated carbon stored in vegetation is 542PgC, compared to an observation-based range of 400-600PgC. Soil carbon is much lower (1422PgC) than estimates from measurements ( > 2400PgC), with large underestimations of soil carbon in the tropical and boreal forests. We also examined some aspects of the historical terrestrial carbon sink as simulated by JULES. Between the 1900s and 2000s, increased atmospheric carbon dioxide levels enhanced vegetation productivity and litter inputs into the soils, while land use change removed vegetation and reduced soil carbon. The result is a simulated increase in soil carbon of 57PgC but a decrease in vegetation carbon of 98PgC. The total simulated loss of soil and vegetation carbon due to land use change is 138PgC from 1900 to 2009, compared to a recent observationally constrained estimate of 15550PgC from 1901 to 2012. The simulated land carbon sink is 2.01.0PgCyrg'1 from 2000 to 2009, in close agreement with estimates from the IPCC and Global Carbon Project.
Abstract.
2017
Rogers A, Medlyn BE, Dukes JS, Bonan G, von Caemmerer S, Dietze MC, Kattge J, Leakey ADB, Mercado LM, Niinemets Ü, et al (2017). A roadmap for improving the representation of photosynthesis in Earth system models.
New Phytol,
213(1), 22-42.
Abstract:
A roadmap for improving the representation of photosynthesis in Earth system models.
Accurate representation of photosynthesis in terrestrial biosphere models (TBMs) is essential for robust projections of global change. However, current representations vary markedly between TBMs, contributing uncertainty to projections of global carbon fluxes. Here we compared the representation of photosynthesis in seven TBMs by examining leaf and canopy level responses of photosynthetic CO2 assimilation (A) to key environmental variables: light, temperature, CO2 concentration, vapor pressure deficit and soil water content. We identified research areas where limited process knowledge prevents inclusion of physiological phenomena in current TBMs and research areas where data are urgently needed for model parameterization or evaluation. We provide a roadmap for new science needed to improve the representation of photosynthesis in the next generation of terrestrial biosphere and Earth system models.
Abstract.
Author URL.
Huntingford C, Atkin OK, Martinez-de la Torre A, Mercado LM, Heskel MA, Harper AB, Bloomfield KJ, O'Sullivan OS, Reich PB, Wythers KR, et al (2017). Implications of improved representations of plant respiration in a changing climate.
NATURE COMMUNICATIONS,
8 Author URL.
Smart SM, Glanville HC, Blanes MDC, Mercado LM, Emmett BA, Jones DL, Cosby BJ, Marrs RH, Butler A, Marshall MR, et al (2017). Leaf dry matter content is better at predicting above‐ground net primary production than specific leaf area. Functional Ecology, 31(6), 1336-1344.
Moreira DS, Longo KM, Freitas SR, Yamasoe MA, Mercado LM, Rosário NE, Gloor E, Viana RSM, Miller JB, Gatti LV, et al (2017). Modeling the radiative effects of biomass burning aerosols on carbon fluxes in the Amazon region.
Atmospheric Chemistry and Physics,
17(23), 14785-14810.
Abstract:
Modeling the radiative effects of biomass burning aerosols on carbon fluxes in the Amazon region
Every year, a dense smoke haze covers a large portion of South America originating from fires in the Amazon Basin and central parts of Brazil during the dry biomass burning season between August and October. Over a large portion of South America, the average aerosol optical depth at 550 nm exceeds 1.0 during the fire season, while the background value during the rainy season is below 0.2. Biomass burning aerosol particles increase scattering and absorption of the incident solar radiation. The regional-scale aerosol layer reduces the amount of solar energy reaching the surface, cools the near-surface air, and increases the diffuse radiation fraction over a large disturbed area of the Amazon rainforest. These factors affect the energy and CO2 fluxes at the surface. In this work, we applied a fully integrated atmospheric model to assess the impact of biomass burning aerosols in CO2 fluxes in the Amazon region during 2010. We address the effects of the attenuation of global solar radiation and the enhancement of the diffuse solar radiation flux inside the vegetation canopy. Our results indicate that biomass burning aerosols led to increases of about 27% in the gross primary productivity of Amazonia and 10% in plant respiration as well as a decline in soil respiration of 3 %. Consequently, in our model Amazonia became a net carbon sink; net ecosystem exchange during September 2010 dropped from C101 to 104 TgC when the aerosol effects are considered, mainly due to the aerosol diffuse radiation effect. For the forest biome, our results point to a dominance of the diffuse radiation effect on CO2 fluxes, reaching a balance of 50-50% between the diffuse and direct aerosol effects for high aerosol loads. For C3 grasses and savanna (cerrado), as expected, the contribution of the diffuse radiation effect is much lower, tending to zero with the increase in aerosol load. Taking all biomes together, our model shows the Amazon during the dry season, in the presence of high biomass burning aerosol loads, changing from being a source to being a sink of CO2 to the atmosphere.
Abstract.
2016
Rowland LM, Meir P, Mencuccini M, Binks OJ, da Costa ACL, Oliveria RS, Mercado L, Vasconcelos SS, de Oliveria AAR, Christoffersen BO, et al (2016). Does inter-specific variation prevent division of tropical trees into drought sensitive and resistant groups?. Association of tropical Biology and Conservation. 19th - 23rd Jun 2016.
Abstract:
Does inter-specific variation prevent division of tropical trees into drought sensitive and resistant groups?
Abstract.
Huntingford C, Mercado LM (2016). High chance that current atmospheric greenhouse concentrations commit to warmings greater than 1.5°C over land.
Scientific Reports,
6Abstract:
High chance that current atmospheric greenhouse concentrations commit to warmings greater than 1.5°C over land
The recent Paris UNFCCC climate meeting discussed the possibility of limiting global warming to 2 °C since pre-industrial times, or possibly even 1.5 °C, which would require major future emissions reductions. However, even if climate is stabilised at current atmospheric greenhouse gas (GHG) concentrations, those warming targets would almost certainly be surpassed in the context of mean temperature increases over land only. The reason for this is two-fold. First, current transient warming lags significantly below equilibrium or "committed" warming. Second, almost all climate models indicate warming rates over land are much higher than those for the oceans. We demonstrate this potential for high eventual temperatures over land, even for contemporary GHG levels, using a large set of climate models and for which climate sensitivities are known. Such additional land warming has implications for impacts on terrestrial ecosystems and human well-being. This suggests that even if massive and near-immediate emissions reductions occur such that atmospheric GHGs increase further by only small amounts, careful planning is needed by society to prepare for higher land temperatures in an eventual equilibrium climatic state.
Abstract.
Harper AB, Cox PM, Friedlingstein P, Wiltshire AJ, Jones CD, Sitch S, Mercado LM, Groenendijk M, Robertson E, Kattge J, et al (2016). Improved representation of plant functional types and physiology in the Joint UK Land Environment Simulator (JULES v4.2) using plant trait information.
Geoscientific Model Development,
9(7), 2415-2440.
Abstract:
Improved representation of plant functional types and physiology in the Joint UK Land Environment Simulator (JULES v4.2) using plant trait information
Dynamic global vegetation models are used to predict the response of vegetation to climate change. They are essential for planning ecosystem management, understanding carbon cycle-climate feedbacks, and evaluating the potential impacts of climate change on global ecosystems. JULES (the Joint UK Land Environment Simulator) represents terrestrial processes in the UK Hadley Centre family of models and in the first generation UK Earth System Model. Previously, JULES represented five plant functional types (PFTs): broadleaf trees, needle-leaf trees, C3 and C4 grasses, and shrubs. This study addresses three developments in JULES. First, trees and shrubs were split into deciduous and evergreen PFTs to better represent the range of leaf life spans and metabolic capacities that exists in nature. Second, we distinguished between temperate and tropical broadleaf evergreen trees. These first two changes result in a new set of nine PFTs: tropical and temperate broadleaf evergreen trees, broadleaf deciduous trees, needle-leaf evergreen and deciduous trees, C3 and C4 grasses, and evergreen and deciduous shrubs. Third, using data from the TRY database, we updated the relationship between leaf nitrogen and the maximum rate of carboxylation of Rubisco (Vcmax), and updated the leaf turnover and growth rates to include a trade-off between leaf life span and leaf mass per unit area. Overall, the simulation of gross and net primary productivity (GPP and NPP, respectively) is improved with the nine PFTs when compared to FLUXNET sites, a global GPP data set based on FLUXNET, and MODIS NPP. Compared to the standard five PFTs, the new nine PFTs simulate a higher GPP and NPP, with the exception of C3 grasses in cold environments and C4 grasses that were previously over-productive. On a biome scale, GPP is improved for all eight biomes evaluated and NPP is improved for most biomes - the exceptions being the tropical forests, savannahs, and extratropical mixed forests where simulated NPP is too high. With the new PFTs, the global present-day GPP and NPP are 128 and 62 Pg C year-1, respectively. We conclude that the inclusion of trait-based data and the evergreen/deciduous distinction has substantially improved productivity fluxes in JULES, in particular the representation of GPP. These developments increase the realism of JULES, enabling higher confidence in simulations of vegetation dynamics and carbon storage.
Abstract.
Rowland LM, da Costa ACL, Oliveira RS, Binks OJ, Mercado L, Vasconcelos SS, de Oliveira AAR, Salmon Y, Ferreira LV, Sitch S, et al (2016). Is sap flow a good indicator of drought-induced mortality risk in tropical rainforest. Association of Tropical Biology and Conservation. 19th - 23rd Jun 2016.
Abstract:
Is sap flow a good indicator of drought-induced mortality risk in tropical rainforest.
Abstract.
2015
Huntingford C, Smith DM, Davies WJ, Falk R, Sitch S, Mercado LM (2015). Combining the [ABA] and net photosynthesis-based model equations of stomatal conductance.
Ecological Modelling,
300, 81-88.
Abstract:
Combining the [ABA] and net photosynthesis-based model equations of stomatal conductance
Stomatal conductance gs is variously depicted as being dependent on environmental conditions (Jarvis, 976), transpiration (Monteith, 1995), net photosynthesis (Leuning, 1995) or chemical signalling arriving in the xylem (Tardieu and Davies, 1993). Accurate descriptions of gs are being increasingly demanded in the large-scale land surface model components of General Circulation Models (GCMs) to predict future land-atmospheric fluxes of water vapour, heat and carbon dioxide. The JULES model, for instance, uses the net photosynthesis description combined with a relatively simple semi-linear dependence on soil moisture content that modulates the photosynthesis dependence (Cox et al. 1998).Dewar (2002) combines the Leuning (1995) and Tardieu and Davies (1993) models. We revisit that combination, and discuss whether the Vapour Pressure Deficit (VPD) implicit in both components is different or in common. Further, we show a potential re-arrangement of the combined equations reveals that this model for gs can be considered as being dependent on only four variables: evaporative flux Jw, net photosynthesis an, soil moisture content θ and ambient CO2 concentration ca. Expressed this way, gs is influenced by two relatively slowly varying stores of the hydrological and carbon cycles (soil water content and atmospheric CO2) and two more rapidly fluctuating fluxes from both cycles (evaporation and net photosynthesis). We consider how the modelling structure and its response to both canopy-level and soil environmental controls may make it suitable for inclusion in GCMs, and what this entails in terms of parameterisation.
Abstract.
Baig S, Medlyn BE, Mercado LM, Zaehle S (2015). Does the growth response of woody plants to elevated CO<inf>2</inf> increase with temperature? a model-oriented meta-analysis.
Global Change Biology,
21(12), 4303-4319.
Abstract:
Does the growth response of woody plants to elevated CO2 increase with temperature? a model-oriented meta-analysis
The temperature dependence of the reaction kinetics of the Rubisco enzyme implies that, at the level of a chloroplast, the response of photosynthesis to rising atmospheric CO2 concentration (Ca) will increase with increasing air temperature. Vegetation models incorporating this interaction predict that the response of net primary productivity (NPP) to elevated CO2 (eCa) will increase with rising temperature and will be substantially larger in warm tropical forests than in cold boreal forests. We tested these model predictions against evidence from eCa experiments by carrying out two meta-analyses. Firstly, we tested for an interaction effect on growth responses in factorial eCa × temperature experiments. This analysis showed a positive, but nonsignificant interaction effect (95% CI for above-ground biomass response = -0.8, 18.0%) between eCa and temperature. Secondly, we tested field-based eCa experiments on woody plants across the globe for a relationship between the eCa effect on plant biomass and mean annual temperature (MAT). This second analysis showed a positive but nonsignificant correlation between the eCa response and MAT. The magnitude of the interactions between CO2 and temperature found in both meta-analyses were consistent with model predictions, even though both analyses gave nonsignificant results. Thus, we conclude that it is not possible to distinguish between the competing hypotheses of no interaction vs. an interaction based on Rubisco kinetics from the available experimental database. Experiments in a wider range of temperature zones are required. Until such experimental data are available, model predictions should aim to incorporate uncertainty about this interaction.
Abstract.
Rap A, Spracklen DV, Mercado L, Reddington CL, Haywood JM, Ellis RJ, Phillips OL, Artaxo P, Bonal D, Restrepo Coupe N, et al (2015). Fires increase Amazon forest productivity through increases in diffuse radiation.
Geophysical Research Letters,
42(11), 4654-4662.
Abstract:
Fires increase Amazon forest productivity through increases in diffuse radiation
Atmospheric aerosol scatters solar radiation increasing the fraction of diffuse radiation and the efficiency of photosynthesis. We quantify the impacts of biomass burning aerosol (BBA) on diffuse radiation and plant photosynthesis across Amazonia during 1998-2007. Evaluation against observed aerosol optical depth allows us to provide lower and upper BBA emissions estimates. BBA increases Amazon basin annual mean diffuse radiation by 3.4-6.8% and net primary production (NPP) by 1.4-2.8%, with quoted ranges driven by uncertainty in BBA emissions. The enhancement of Amazon basin NPP by 78-156 Tg C a-1 is equivalent to 33-65% of the annual regional carbon emissions from biomass burning. This NPP increase occurs during the dry season and acts to counteract some of the observed effect of drought on tropical production. We estimate that 30-60 Tg C a-1 of this NPP enhancement is within woody tissue, accounting for 8-16% of the observed carbon sink across mature Amazonian forests.
Abstract.
Atkin OK, Bloomfield KJ, Reich PB, Tjoelker MG, Asner GP, Bonal D, Bönisch G, Bradford MG, Cernusak LA, Cosio EG, et al (2015). Global variability in leaf respiration in relation to climate, plant functional types and leaf traits.
New Phytologist,
206(2), 614-636.
Abstract:
Global variability in leaf respiration in relation to climate, plant functional types and leaf traits
Summary: Leaf dark respiration (R dark ) is an important yet poorly quantified component of the global carbon cycle. Given this, we analyzed a new global database of R dark and associated leaf traits. Data for 899 species were compiled from 100 sites (from the Arctic to the tropics). Several woody and nonwoody plant functional types (PFTs) were represented. Mixed-effects models were used to disentangle sources of variation in R dark. Area-based R dark at the prevailing average daily growth temperature (T) of each site increased only twofold from the Arctic to the tropics, despite a 20°C increase in growing T (8-28°C). By contrast, R dark at a standard T (25°C, R dark25 ) was threefold higher in the Arctic than in the tropics, and twofold higher at arid than at mesic sites. Species and PFTs at cold sites exhibited higher R dark25 at a given photosynthetic capacity (V cmax25 ) or leaf nitrogen concentration ([N]) than species at warmer sites. R dark25 values at any given V cmax25 or [N] were higher in herbs than in woody plants. The results highlight variation in R dark among species and across global gradients in T and aridity. In addition to their ecological significance, the results provide a framework for improving representation of R dark in terrestrial biosphere models (TBMs) and associated land-surface components of Earth system models (ESMs).
Abstract.
2014
Fyllas NM, Gloor E, Mercado LM, Sitch S, Quesada CA, Domingues TF, Galbraith DR, Torre-Lezama A, Vilanova E, Ramírez-Angulo H, et al (2014). Analysing Amazonian forest productivity using a new individual and trait-based model (TFS v.1).
Geoscientific Model Development,
7(4), 1251-1269.
Abstract:
Analysing Amazonian forest productivity using a new individual and trait-based model (TFS v.1)
Repeated long-term censuses have revealed large-scale spatial patterns in Amazon basin forest structure and dynamism, with some forests in the west of the basin having up to a twice as high rate of aboveground biomass production and tree recruitment as forests in the east. Possible causes for this variation could be the climatic and edaphic gradients across the basin and/or the spatial distribution of tree species composition. To help understand causes of this variation a new individual-based model of tropical forest growth, designed to take full advantage of the forest census data available from the Amazonian Forest Inventory Network (RAINFOR), has been developed. The model allows for within-stand variations in tree size distribution and key functional traits and between-stand differences in climate and soil physical and chemical properties. It runs at the stand level with four functional traits - leaf dry mass per area (Ma), leaf nitrogen (NL) and phosphorus (PL) content and wood density (DW) varying from tree to tree - in a way that replicates the observed continua found within each stand. We first applied the model to validate canopy-level water fluxes at three eddy covariance flux measurement sites. For all three sites the canopy-level water fluxes were adequately simulated. We then applied the model at seven plots, where intensive measurements of carbon allocation are available. Tree-by-tree multi-annual growth rates generally agreed well with observations for small trees, but with deviations identified for larger trees. At the stand level, simulations at 40 plots were used to explore the influence of climate and soil nutrient availability on the gross (ΠG) and net (ΠN) primary production rates as well as the carbon use efficiency (CU). Simulated ΠG, ΠN and CU were not associated with temperature. On the other hand, all three measures of stand level productivity were positively related to both mean annual precipitation and soil nutrient status. Sensitivity studies showed a clear importance of an accurate parameterisation of within- and between-stand trait variability on the fidelity of model predictions. For example, when functional tree diversity was not included in the model (i.e. with just a single plant functional type with mean basin-wide trait values) the predictive ability of the model was reduced. This was also the case when basin-wide (as opposed to site-specific) trait distributions were applied within each stand. We conclude that models of tropical forest carbon, energy and water cycling should strive to accurately represent observed variations in functionally important traits across the range of relevant scales. © Author(s) 2014.
Abstract.
2013
Moreira DS, Freitas SR, Bonatti JP, Mercado LM, É. Rosário NM, Longo KM, Miller JB, Gloor M, Gatti LV (2013). Coupling between the JULES land-surface scheme and the CCATT-BRAMS atmospheric chemistry model (JULES-CCATT-BRAMS1.0): Applications to numerical weather forecasting and the CO2 budget in South America.
Geoscientific Model Development,
6(4), 1243-1259.
Abstract:
Coupling between the JULES land-surface scheme and the CCATT-BRAMS atmospheric chemistry model (JULES-CCATT-BRAMS1.0): Applications to numerical weather forecasting and the CO2 budget in South America
This article presents the coupling of the JULES surface model to the CCATT-BRAMS atmospheric chemistry model. This new numerical system is denominated JULES-CCATT-BRAMS. We demonstrate the performance of this new model system in relation to several meteorological variables and the CO2 mixing ratio over a large part of South America, focusing on the Amazon basin. The evaluation was conducted for two time periods, the wet (March) and dry (September) seasons of 2010. The model errors were calculated in relation to meteorological observations at conventional stations in airports and automatic stations. In addition, CO2 mixing ratios in the first model level were compared with meteorological tower measurements and vertical CO2 profiles were compared with observations obtained with airborne instruments. The results of this study show that the JULES-CCATT-BRAMS modeling system provided a significant gain in performance for the considered atmospheric fields relative to those simulated by the LEAF (version 3) surface model originally employed by CCATT-BRAMS. In addition, the new system significantly increases the ability to simulate processes involving air-surface interactions, due to the ability of JULES to simulate photosynthesis, respiration and dynamic vegetation, among other processes. We also discuss a wide range of numerical studies involving coupled atmospheric, land surface and chemistry processes that could be done with the system introduced here. Thus, this work presents to the scientific community a free modeling tool, with good performance in comparison with observational data and reanalysis model data, at least for the region and time period discussed here. Therefore, in principle, this model is able to produce atmospheric hindcast/forecast simulations at different spatial resolutions for any time period and any region of the globe. © Author(s) 2013.
Abstract.
Huntingford C, Mercado L (2013). EARTH SCIENCE the timing of climate change.
NATURE,
502(7470), 174-174.
Author URL.
Huntingford C, Zelazowski P, Galbraith D, Mercado LM, Sitch S, Fisher R, Lomas M, Walker AP, Jones CD, Booth BBB, et al (2013). Simulated resilience of tropical rainforests to CO<inf>2</inf> -induced climate change.
Nature Geoscience,
6(4), 268-273.
Abstract:
Simulated resilience of tropical rainforests to CO2 -induced climate change
How tropical forest carbon stocks might alter in response to changes in climate and atmospheric composition is uncertain. However, assessing potential future carbon loss from tropical forests is important for evaluating the efficacy of programmes for reducing emissions from deforestation and degradation. Uncertainties are associated with different carbon stock responses in models with different representations of vegetation processes on the one hand, and differences in projected changes in temperature and precipitation patterns on the other hand. Here we present a systematic exploration of these sources of uncertainty, along with uncertainty arising from different emissions scenarios for all three main tropical forest regions: the Americas (that is, Amazonia and Central America), Africa and Asia. Using simulations with 22 climate models and the MOSES-TRIFFID land surface scheme, we find that only in one of the simulations are tropical forests projected to lose biomass by the end of the twenty-first century - and then only for the Americas. When comparing with alternative models of plant physiological processes, we find that the largest uncertainties are associated with plant physiological responses, and then with future emissions scenarios. Uncertainties from differences in the climate projections are significantly smaller. Despite the considerable uncertainties, we conclude that there is evidence of forest resilience for all three regions. © 2013 Macmillan Publishers Limited. All rights reserved.
Abstract.
2012
Arneth A, Mercado L, Kattge J, Booth B (2012). Future challenges of representing land-processes in studies on land-atmosphere interactions. , 9(3), 3545-3577.
Arneth A, Mercado L, Kattge J, Booth BBB (2012). Future challenges of representing land-processes in studies on land-atmosphere interactions.
Biogeosciences,
9(9), 3587-3599.
Abstract:
Future challenges of representing land-processes in studies on land-atmosphere interactions
Over recent years, it has become increasingly apparent that climate change and air pollution need to be considered jointly for improved attribution and projections of human-caused changes in the Earth system. Exchange processes at the land surface come into play in this context, because many compounds that either act as greenhouse gases, as pollutant precursors, or both, have not only anthropogenic but also terrestrial sources and sinks. and since the fluxes of multiple gases and particulate matter between the terrestrial biota and the atmosphere are directly or indirectly coupled to vegetation and soil carbon, nutrient and water balances, quantification of their geographic patterns or changes over time requires due consideration of the underlying biological processes. In this review we highlight a number of critical aspects and recent progress in this respect, identifying in particular a number of areas where studies have shown that accounting for ecological process understanding can alter global model projections of land-atmosphere interactions substantially. Specifically, this concerns the improved quantification of uncertainties and dynamic system responses, including acclimation, and the incorporation of exchange processes that so far have been missing from global models even though they are proposed to be of relevance for our understanding of terrestrial biota-climate feedbacks. Progress has also been made regarding studies on the impacts of land use/land cover change on climate change, but the absence of a mechanistically based representation of human response-processes in ecosystem models that are coupled to climate models limits our ability to analyse how climate change or air pollution in turn might affect human land use. A more integrated perspective is necessary and should become an active area of research that bridges the socio-economic and biophysical communities. © 2012 Author(s).
Abstract.
Marthews TR, Malhi Y, Girardin CAJ, Silva Espejo JE, Aragão LEOC, Metcalfe DB, Rapp JM, Mercado LM, Fisher RA, Galbraith DR, et al (2012). Simulating forest productivity along a neotropical elevational transect: Temperature variation and carbon use efficiency.
Global Change Biology,
18(9), 2882-2898.
Abstract:
Simulating forest productivity along a neotropical elevational transect: Temperature variation and carbon use efficiency
A better understanding of the mechanisms controlling the magnitude and sign of carbon components in tropical forest ecosystems is important for reliable estimation of this important regional component of the global carbon cycle. We used the JULES vegetation model to simulate all components of the carbon balance at six sites along an Andes-Amazon transect across Peru and Brazil and compared the results to published field measurements. In the upper montane zone the model predicted a lack of forest vegetation, indicating a need for better parameterization of the responses of cloud forest vegetation within the model. In the lower montane and lowland zones simulated ecosystem productivity and respiration were predicted with reasonable accuracy, although not always within the error bounds of the observations. Model-predicted carbon use efficiency in this transect surprisingly did not increase with elevation, but remained close to the 'temperate' value 0.5. Upper montane forests were predicted to allocate ~50% of carbon fixation to biomass maintenance and growth, despite available measurements showing that they only allocate ~33%. This may be explained by elevational changes in the balance between growth and maintenance respiration within the forest canopy, as controlled by both temperature- and pressure-mediated processes, which is not yet well represented in current vegetation models. © 2012 Blackwell Publishing Ltd.
Abstract.
2011
Mercado LM, Lloyd J, Dolman AJ, Sitch S, Patiño S (2011). Erratum: Modelling basin-wide variations in Amazon forest productivity &ndash; Part 1: Model calibration, evaluation and upscaling functions for canopy photosynthesis" published in Biogeosciences, 6, 1247&ndash;1272, 2009 (Biogeosciences). Biogeosciences, 8(3), 653-656.
Huntingford C, Cox PM, Mercado LM, Sitch S, Bellouin N, Boucher O, Gedney N (2011). Highly contrasting effects of different climate forcing agents on terrestrial ecosystem services.
Philos Trans a Math Phys Eng Sci,
369(1943), 2026-2037.
Abstract:
Highly contrasting effects of different climate forcing agents on terrestrial ecosystem services.
Many atmospheric constituents besides carbon dioxide (CO(2)) contribute to global warming, and it is common to compare their influence on climate in terms of radiative forcing, which measures their impact on the planetary energy budget. A number of recent studies have shown that many radiatively active constituents also have important impacts on the physiological functioning of ecosystems, and thus the 'ecosystem services' that humankind relies upon. CO(2) increases have most probably increased river runoff and had generally positive impacts on plant growth where nutrients are non-limiting, whereas increases in near-surface ozone (O(3)) are very detrimental to plant productivity. Atmospheric aerosols increase the fraction of surface diffuse light, which is beneficial for plant growth. To illustrate these differences, we present the impact on net primary productivity and runoff of higher CO(2), higher near-surface O(3), and lower sulphate aerosols, and for equivalent changes in radiative forcing. We compare this with the impact of climate change alone, arising, for example, from a physiologically inactive gas such as methane (CH(4)). For equivalent levels of change in radiative forcing, we show that the combined climate and physiological impacts of these individual agents vary markedly and in some cases actually differ in sign. This study highlights the need to develop more informative metrics of the impact of changing atmospheric constituents that go beyond simple radiative forcing.
Abstract.
Author URL.
Best MJ, Pryor M, Clark DB, Rooney GG, Essery RLH, Ménard CB, Edwards JM, Hendry MA, Porson A, Gedney N, et al (2011). The Joint UK Land Environment Simulator (JULES), Model description – Part 1: Energy and water fluxes. , 4(1), 595-640.
Clark DB, Mercado LM, Sitch S, Jones CD, Gedney N, Best MJ, Pryor M, Rooney GG, Essery RLH, Blyth E, et al (2011). The Joint UK Land Environment Simulator (JULES), Model description – Part 2: Carbon fluxes and vegetation. , 4(1), 641-688.
Best MJ, Pryor M, Clark DB, Rooney GG, Essery RLH, Menard CB, Edwards JM, Hendry MA, Porson A, Gedney N, et al (2011). The Joint UK Land Environment Simulator (JULES), model description - Part 1: Energy and water fluxes.
GEOSCIENTIFIC MODEL DEVELOPMENT,
4(3), 677-699.
Author URL.
Clark DB, Mercado LM, Sitch S, Jones CD, Gedney N, Best MJ, Pryor M, Rooney GG, Essery RLH, Blyth E, et al (2011). The Joint UK Land Environment Simulator (JULES), model description - Part 2: Carbon fluxes and vegetation dynamics.
GEOSCIENTIFIC MODEL DEVELOPMENT,
4(3), 701-722.
Author URL.
Mercado LM, Patiño S, Domingues TF, Fyllas NM, Weedon GP, Sitch S, Quesada CA, Phillips OL, Aragão LEOC, Malhi Y, et al (2011). Variations in Amazon forest productivity correlated with foliar nutrients and modelled rates of photosynthetic carbon supply.
Philos Trans R Soc Lond B Biol Sci,
366(1582), 3316-3329.
Abstract:
Variations in Amazon forest productivity correlated with foliar nutrients and modelled rates of photosynthetic carbon supply.
The rate of above-ground woody biomass production, W(P), in some western Amazon forests exceeds those in the east by a factor of 2 or more. Underlying causes may include climate, soil nutrient limitations and species composition. In this modelling paper, we explore the implications of allowing key nutrients such as N and P to constrain the photosynthesis of Amazon forests, and also we examine the relationship between modelled rates of photosynthesis and the observed gradients in W(P). We use a model with current understanding of the underpinning biochemical processes as affected by nutrient availability to assess: (i) the degree to which observed spatial variations in foliar [N] and [P] across Amazonia affect stand-level photosynthesis; and (ii) how these variations in forest photosynthetic carbon acquisition relate to the observed geographical patterns of stem growth across the Amazon Basin. We find nutrient availability to exert a strong effect on photosynthetic carbon gain across the Basin and to be a likely important contributor to the observed gradient in W(P). Phosphorus emerges as more important than nitrogen in accounting for the observed variations in productivity. Implications of these findings are discussed in the context of future tropical forests under a changing climate.
Abstract.
Author URL.
2010
Huntingford C, Booth BBB, Sitch S, Gedney N, Lowe JA, Liddicoat SK, Mercado LM, Best MJ, Weedon GP, Fisher RA, et al (2010). IMOGEN: an intermediate complexity model to evaluate terrestrial impacts of a changing climate.
GEOSCIENTIFIC MODEL DEVELOPMENT,
3(2), 679-687.
Author URL.
Huntingford C, Booth BBB, Sitch S, Gedney N, Lowe JA, Liddicoat SK, Mercado LM, Best MJ, Weedon GP, Fisher RA, et al (2010). IMOGEN: an intermediate complexity model to evaluate terrestrial impacts of a changing climate. , 3(3), 1161-1184.
Lloyd J, Patiño S, Paiva RQ, Nardoto GB, Quesada CA, Santos AJB, Baker TR, Brand WA, Hilke I, Gielmann H, et al (2010). Optimisation of photosynthetic carbon gain and within-canopy gradients of associated foliar traits for Amazon forest trees. Biogeosciences, 7, 1833-1859.
2009
Fyllas NM, Patino S, Baker TR, Bielefeld Nardoto G, Martinelli LA, Quesada CA, Paiva R, Schwarz M, Horna V, Mercado LM, et al (2009). Basin-wide variations in foliar properties of Amazonian forest: Phylogeny, soils and climate.
Biogeosciences,
6(11), 2677-2708.
Abstract:
Basin-wide variations in foliar properties of Amazonian forest: Phylogeny, soils and climate
We analysed 1040 individual trees, located in 62 plots across the Amazon Basin for leaf mass per unit area (MA), foliar carbon isotopic composition (δ13C) and leaf level concentrations of C, N, P, Ca, Mg, K and Al. All trees were identified to the species level with the dataset containing 58 families, 236 genera and 508 species, distributed across a wide range of soil types and precipitation regimes. Some foliar characteristics such as MA, [C], [N] and [Mg] emerge as highly constrained by the taxonomic affiliation of tree species, but with others such as [P], [K], [Ca] and δ13C also strongly influenced by site growing conditions. By removing the environmental contribution to trait variation, we find that intrinsic values of most trait pairs coordinate, although different species (characterised by different trait suites) are found at discrete locations along a common axis of coordination. Species that tend to occupy higher fertility soils are characterised by a lower MA and have a higher intrinsic [N], [P], [K], [Mg] and δ13C than their lower fertility counterparts. Despite this consistency, different scaling patterns were observed between low and high fertility sites. Inter-relationships are thus substantially modified by growth environment. Analysing the environmental component of trait variation, we found soil fertility to be the most important predictor, influencing all leaf nutrient concentrations and δ 13C and reducing MA. Mean annual temperature was negatively associated with leaf level [N], [P] and [K] concentrations. Total annual precipitation positively influences MA, [C] and δ13C, but with a negative impact on [Mg]. These results provide a first basis for understanding the relationship between the physiological functioning and distribution of tree species across Amazonia.
Abstract.
Fyllas NM, Patiño S, Baker TR, Nardoto GB, Martinelli LA, Quesada CA, Paiva R, Schwarz M, Horna V, Mercado LM, et al (2009). Basin-wide variations in foliar properties of Amazonian forest: phylogeny, soils and climate. , 6(2), 3707-3769.
Patino S, Lloyd J, Paiva R, Baker TR, Quesada CA, Mercado LM, Schmerler J, Schwarz M, Santos AJB, Aguilar A, et al (2009). Branch xylem density variations across the Amazon Basin.
Biogeosciences,
6(4), 545-568.
Abstract:
Branch xylem density variations across the Amazon Basin
Xylem density is a physical property of wood that varies between individuals, species and environments. It reflects the physiological strategies of trees that lead to growth, survival and reproduction. Measurements of branch xylem density, ρx , were made for 1653 trees representing 598 species, sampled from 87 sites across the Amazon basin. Measured values ranged from 218 kgm-3 for a Cordia sagotii (Boraginaceae) from Mountagne de Tortue, French Guiana to 1130 kgm-3 for an Aiouea sp. (Lauraceae) from Caxiuana, Central Pará, Brazil. Analysis of variance showed significant differences in average ρx across regions and sampled plots as well as significant differences between families, genera and species. A partitioning of the total variance in the dataset showed that species identity (family, genera and species) accounted for 33% with environment (geographic location and plot) accounting for an additional 26%; the remaining "residual" variance accounted for 41% of the total variance. Variations in plot means, were, however, not only accountable by differences in species composition because xylem density of the most widely distributed species in our dataset varied systematically from plot to plot. Thus, as well as having a genetic component, branch xylem density is a plastic trait that, for any given species, varies according to where the tree is growing in a predictable manner. Within the analysed taxa, exceptions to this general rule seem to be pioneer species belonging for example to the Urticaceae whose branch xylem density is more constrained than most species sampled in this study. These patterns of variation of branch xylem density across Amazonia suggest a large functional diversity amongst Amazonian trees which is not well understood. © Author(s) 2009.
Abstract.
Mercado LM, Bellouin N, Sitch S, Boucher O, Huntingford C, Wild M, Cox PM (2009). Impact of changes in diffuse radiation on the global land carbon sink.
Nature,
458(7241), 1014-1017.
Abstract:
Impact of changes in diffuse radiation on the global land carbon sink.
Plant photosynthesis tends to increase with irradiance. However, recent theoretical and observational studies have demonstrated that photosynthesis is also more efficient under diffuse light conditions. Changes in cloud cover or atmospheric aerosol loadings, arising from either volcanic or anthropogenic emissions, alter both the total photosynthetically active radiation reaching the surface and the fraction of this radiation that is diffuse, with uncertain overall effects on global plant productivity and the land carbon sink. Here we estimate the impact of variations in diffuse fraction on the land carbon sink using a global model modified to account for the effects of variations in both direct and diffuse radiation on canopy photosynthesis. We estimate that variations in diffuse fraction, associated largely with the 'global dimming' period, enhanced the land carbon sink by approximately one-quarter between 1960 and 1999. However, under a climate mitigation scenario for the twenty-first century in which sulphate aerosols decline before atmospheric CO(2) is stabilized, this 'diffuse-radiation' fertilization effect declines rapidly to near zero by the end of the twenty-first century.
Abstract.
Author URL.
Mercado LM, Lloyd J, Dolman AJ, Sitch S, Patiño S (2009). Modelling basin-wide variations in Amazon forest productivity - Part 1: Model calibration, evaluation and upscaling functions for canopy photosynthesis.
Biogeosciences,
6(7), 1247-1272.
Abstract:
Modelling basin-wide variations in Amazon forest productivity - Part 1: Model calibration, evaluation and upscaling functions for canopy photosynthesis
Given the importance of Amazon rainforest in the global carbon and hydrological cycles, there is a need to parameterize and validate ecosystem gas exchange and vegetation models for this region in order to adequately simulate present and future carbon and water balances. In this study, a sun and shade canopy gas exchange model is calibrated and evaluated at five rainforest sites using eddy correlation measurements of carbon and energy fluxes. Results from the model-data evaluation suggest that with adequate parameterisation, photosynthesis models taking into account the separation of diffuse and direct irradiance and the dynamics of sunlit and shaded leaves can accurately represent photosynthesis in these forests. Also, stomatal conductance formulations that only take into account atmospheric demand fail to correctly simulate moisture and CO2 fluxes in forests with a pronounced dry season, particularly during afternoon conditions. Nevertheless, it is also the case that large uncertainties are associated not only with the eddy correlation data, but also with the estimates of ecosystem respiration required for model validation. To accurately simulate Gross Primary Productivity (GPP) and energy partitioning the most critical parameters and model processes are the quantum yield of photosynthetic uptake, the maximum carboxylation capacity of Rubisco, and simulation of stomatal conductance. © Author(s) 2009.
Abstract.
Mercado LM, Lloyd J, Dolman AJ, Sitch S, Patiño S (2009). Modelling basin-wide variations in Amazon forest productivity – Part 1: Model calibration, evaluation and upscaling functions for canopy photosynthesis. , 6(2), 2965-3030.
Lloyd J, Patiño S, Paiva RQ, Nardoto GB, Quesada CA, Santos AJB, Baker TR, Brand WA, Hilke I, Gielmann H, et al (2009). Variations in leaf physiological properties within Amazon forest canopies. , 6(3), 4639-4692.
2008
Huntingford C, Fisher RA, Mercado L, Booth BBB, Sitch S, Harris PP, Cox PM, Jones CD, Betts RA, Malhi Y, et al (2008). "Towards quantifying uncertainty in predictions of Amazon """"dieback""""".
Phil. Trans. Roy. Soc. B. Author URL.
Patiño S, Lloyd J, Paiva R, Quesada CA, Baker TR, Santos AJB, Mercado LM, Malhi Y, Phillips OL, Aguilar A, et al (2008). Branch xylem density variations across Amazonia. , 5(3), 2003-2047.
2007
Mercado LM, Huntingford C, Gash JHC, Cox PM, Jogireddy V (2007). Improving the representation of radiation interception and photosynthesis for climate model applications.
TELLUS SERIES B-CHEMICAL AND PHYSICAL METEOROLOGY,
59(3), 553-565.
Author URL.
Mercado LM, Huntingford C, Gash JHC, Cox PM, Jogireddy V (2007). Improving the representation of radiation interception and photosynthesis for climate model applications. Tellus B, 59(3).
2006
Alton P, Mercado L, North P (2006). A sensitivity analysis of the land-surface scheme JULES conducted for three forest biomes: Biophysical parameters, model processes, and meteorological driving data.
Global Biogeochemical Cycles,
21(1).
Abstract:
A sensitivity analysis of the land-surface scheme JULES conducted for three forest biomes: Biophysical parameters, model processes, and meteorological driving data
We conduct a sensitivity/uncertainty analysis of the land-surface scheme JULES focusing on biophysical parameters and model processes that govern light propagation and canopy photosynthesis. We find that current simulations of productivity/energy-exchange are limited as much by their approximate representation of complex physical processes as they are by the accuracy to which their biophysical parameters can be specified. This inference is made for three forest biomes: sparse, boreal needleleaf; dense, tropical broadleaf; and temperate broadleaf of intermediate density. Within the present study, the most influential biophysical parameters are light-limited quantum efficiency (α), the Rubisco-limited rate of photosynthesis at the top of the canopy (Vcmax) and the near-infrared transmittance of vegation (TNIR). Assuming respective, current uncertainties of 0.02, 20 μmol/m2/s and 0.16 in these aforementioned parameters, predictions of Gross Photosynthetic Product (GPP), latent heat (LE), sensible heat (H) and upwelling thermal radiation (R) vary by ∼20%, ∼10%, ∼35% and ∼0.3%, respectively. Current representations of canopy photosynthesis and stomatal conductance yield comparable uncertainties in simulated GPP and LE and a ∼60% uncertainty in H. For canopy photosynthesis, explicit treatment of sunfleck penetration and leaf orientation are important elements in the calculation. of the meteorological variables that drive the land-surface scheme, the downwelling fluxes of radiation in the shortwave and longwave vie in importance with the most influential biophysical parameters. The results from our study are partly biome-dependent. Thus ground albedo and leaf area index (LAI) assume greater importance in sparsely vegetated systems. Copyright 2007 by the American Geophysical Union.
Abstract.
Mercado L, Lloyd J, Carswell F, Malhi Y, Meir P, Nobre AD (2006). Modelling Amazonian forest eddy covariance data: a comparison of big leaf versus sun/shade models for the C-14 tower at Manaus I. Canopy photosynthesis.
Acta Amazonica,
36(1), 69-82.
Abstract:
Modelling Amazonian forest eddy covariance data: a comparison of big leaf versus sun/shade models for the C-14 tower at Manaus I. Canopy photosynthesis
In this study, we concentrate on modelling gross primary productivity using two simple approaches to simulate canopy photosynthesis: "big leaf" and "sun/shade" models. Two approaches for calibration are used: scaling up of canopy photosynthetic parameters from the leaf to the canopy level and fitting canopy biochemistry to eddy covariance fluxes. Validation of the models is achieved by using eddy covariance data from the LBA site C14. Comparing the performance of both models we conclude that numerically (in terms of goodness of fit) and qualitatively, (in terms of residual response to different environmental variables) sun/shade does a better job. Compared to the sun/shade model, the big leaf model shows a lower goodness of fit and fails to respond to variations in the diffuse fraction, also having skewed responses to temperature and VPD. The separate treatment of sun and shade leaves in combination with the separation of the incoming light into direct beam and diffuse make sun/shade a strong modelling tool that catches more of the observed variability in canopy fluxes as measured by eddy covariance. In conclusion, the sun/shade approach is a relatively simple and effective tool for modelling photosynthetic carbon uptake that could be easily included in many terrestrial carbon models.
Abstract.
2004
Malhi Y, Baker TR, Phillips OL, Almeida S, Alvarez E, Arroyo L, Chave J, Czimczik CI, Di Fiore A, Higuchi N, et al (2004). The above-ground coarse wood productivity of 104 Neotropical forest plots.
Global Change Biology,
10(5), 563-591.
Abstract:
The above-ground coarse wood productivity of 104 Neotropical forest plots
The net primary production of tropical forests and its partitioning between long-lived carbon pools (wood) and shorter-lived pools (leaves, fine roots) are of considerable importance in the global carbon cycle. However, these terms have only been studied at a handful of field sites, and with no consistent calculation methodology. Here we calculate above-ground coarse wood carbon productivity for 104 forest plots in lowland New World humid tropical forests, using a consistent calculation methodology that incorporates corrections for spatial variations in tree-size distributions and wood density, and for census interval length. Mean wood density is found to be lower in more productive forests. We estimate that above-ground coarse wood productivity varies by more than a factor of three (between 1.5 and 5.5 Mg C ha-1a-1) across the Neotropical plots, with a mean value of 3.1 Mg C ha-a-1. There appear to be no obvious relationships between wood productivity and rainfall, dry season length or sunshine, but there is some hint of increased productivity at lower temperatures. There is, however, also strong evidence for a positive relationship between wood productivity and soil fertility. Fertile soils tend to become more common towards the Andes and at slightly higher than average elevations, so the apparent temperature/productivity relationship is probably not a direct one. Coarse wood productivity accounts for only a fraction of overall tropical forest net primary productivity, but the available data indicate that it is approximately proportional to total above-ground productivity. We speculate that the large variation in wood productivity is unlikely to directly imply an equivalent variation in gross primary production. Instead a shifting balance in carbon allocation between respiration, wood carbon and fine root production seems the more likely explanation. © 2004 Blackwell Publishing Ltd.
Abstract.
