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3 resultados encontrados para: AUTOR: Le Maire, Guerric
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Evapotranspiration and energy partitioning are complex to estimate because they result from the interaction of many different processes, especially in multi-species and multi-strata ecosystems. We used MAESPA model, a mechanistic, 3D model of coupled radiative transfer, photosynthesis, and balances of energy and water, to simulate the partitioning of energy and evapotranspiration in homogeneous tree plantations, as well as in heterogeneous multi-species, multi-strata agroforests with diverse spatial scales and management schemes. The MAESPA model was modified to add (1) calculation of foliage surface water evaporation at the voxel scale; (2) computation of an average within-canopy air temperature and vapour pressure; and (3) use of (1) and (2) in iterative calculations of soil and leaf temperatures to close ecosystem-level energy balances. We tested MAESPA model simulations on a simple monospecific Eucalyptus stand in Brazil, and also in two complex, heterogeneous Coffea agroforests in Costa Rica. MAESPA satisfactorily simulated the daily and seasonal dynamics of net radiation (RMSE=29.6 and 28.4Wm−²; R²=0.99 and 0.99 for Eucalyptus and Coffea sites respectively) and its partitioning between latent-(RMSE=68.1 and 37.2Wm−²; R²=0.87 and 0.85) and sensible-energy (RMSE=54.6 and 45.8Wm−²; R²=0.57 and 0.88) over a one-year simulation at half-hourly time-step.

After validation, we use the modified MAESPA to calculate partitioning of evapotranspiration and energy between plants and soil in the above-mentioned agro-ecosystems. In the Eucalyptus plantation, 95% of the outgoing energy was emitted as latent-heat, while the Coffea agroforestry system’s partitioning between sensible and latent-heat fluxes was roughly equal. We conclude that MAESPA process-based model has an appropriate balance of detail, accuracy, and computational speed to be applicable to simple or complex forest ecosystems and at different scales for energy and evapotranspiration partitioning.


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Native coffee agroforestry in the Western Ghats of India maintains higher carbon storage and tree diversity compared to exotic agroforestry
Guillemot, Joannès ; Le Maire, Guerric (coaut.) ; Munishamappa, Manjunatha (coaut.) ; Charbonnier, Fabien Sylvain Jacky (coaut.) ; Vaast, Philippe (coaut.) ;
Contenido en: Agriculture, Ecosystems and Environment Vol. 265 (October 2018), p. 461-469 ISSN: 0167-8809
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The ongoing introduction of the exotic Grevillea robusta tree species into agroforestry systems (AFS) of the Indian Western Ghats could become a threat to both climate change mitigation and tree diversity conservation. Here, we quantified carbon (C) storage and shade tree diversity in native forests and coffee AFS under contrasted management (native versus exotic shade trees, Robusta versus Arabica systems) at 67 plots along a 3500mm precipitation gradient in the Cauvery watershed, India. Despite a substantial reduction of shade tree cover in native AFS compared to forest (from 90% to 32% in the high precipitation area), native AFS and forests displayed high and comparable C stocks (max. 228 MgC ha−¹ and 234 MgC ha-¹, respectively) and tree diversity (max. 44 and 45 species, respectively). Both variables were negatively impacted by the introduction of G. robusta, especially in Robusta coffee systems (max. 158 MgC ha−¹, 12 species). The current trend toward the introduction of G. robusta in coffee AFS of the study area (exotic agroforestry) negatively affects C storage and tree diversity, especially in Robusta coffee systems. Policy makers should take advantage of the carbon-tree diversity positive correlation found in the agroforestry landscape of the Western Ghats of India to promote conservation and climate change mitigation.


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In agroforestry systems, shade trees strongly affect the physiology of the undergrown crop. However, a major paradigm is that the reduction in absorbed photosynthetically active radiation is, to a certain extent, compensated by an increase in light-use efficiency, thereby reducing the difference in net primary productivity between shaded and non-shaded plants. Due to the large spatial heterogeneity in agroforestry systems and the lack of appropriate tools, the combined effects of such variables have seldom been analysed, even though they may help understand physiological processes underlying yield dynamics. In this study, we monitored net primary productivity, during two years, on scales ranging from individual coffee plants to the entire plot. Absorbed radiation was mapped with a 3D model (MAESPA). Light-use efficiency and net assimilation rate were derived for each coffee plant individually. We found that although irradiance was reduced by 60% below crowns of shade trees, coffee light-use efficiency increased by 50%, leaving net primary productivity fairly stable across all shade levels. Variability of aboveground net primary productivity of coffee plants was caused primarily by the age of the plants and by intraspecific competition among them (drivers usually overlooked in the agroforestry literature) rather than by the presence of shade trees.