The Experts below are selected from a list of 258 Experts worldwide ranked by ideXlab platform
Luiz Eduardo Oliveira E.cruz De Aragão - One of the best experts on this subject based on the ideXlab platform.
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Seasonal changes in plant-water relations influence patterns of leaf display in Miombo woodlands: evidence of water conservative strategies.
Tree Physiology, 2018Co-Authors: Royd Vinya, Nick D. Brown, Joshua B Fisher, Yadvinder Malhi, Timothy J Brodribb, Luiz Eduardo Oliveira E.cruz De AragãoAbstract:Water availability has frequently been linked to seasonal leaf display in seasonally dry Ecosystems, but there have been few ecohydrological investigations of this link. Miombo woodland is a dominant seasonally dry Tropical Forest Ecosystem type in southern Africa; however, there are few data on the relationship between seasonal dynamics in plant–water relations and patterns of leaf display for Miombo woodland. Here we investigate this relationship among nine key Miombo woodland tree species differing in drought tolerance ability and leaf phenology. Results of this study showed that seasonal patterns of leaf phenology varied significantly with seasonal changes in stem water relations among the nine species. Leaf shedding coincided with the attainment of seasonal minimum stem water potential. Leaf flush occurred following xylem rehydration at the peak of the dry season suggesting that endogenous plant factors play a pivotal role in seasonal leaf display in this Forest type. Drought-tolerant deciduous species suffered significantly higher seasonal losses in xylem hydraulic conductivity than the drought-intolerant semi-evergreen tree species (P < 0.05). There was a significant and positive correlation between species drought tolerance index and species’ seasonal loss in hydraulic conductivity (P < 0.05), confirming the ecological role of long-distance xylem transport in this seasonally dry Tropical Forest. Our results reveal that water stress in seasonally dry Tropical Forests selects for water conservative traits that protect the vulnerable xylem transport system. Therefore, seasonal rhythms in xylem transport dictate patterns of leaf display in seasonally dry Tropical Forests.
Philippe Ciais - One of the best experts on this subject based on the ideXlab platform.
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Seasonal patterns of CO2 fluxes in Amazon Forests: fusion of eddy covariance data and the ORCHIDEE model
Journal of Geophysical Research, 2011Co-Authors: Hans Verbeeck, Philippe Peylin, Cédric Bacour, Damien Bonal, Kathy Steppe, Philippe CiaisAbstract:In some regions of the Amazon, global biogeophysical models have difficulties to reproduce measured seasonal patterns of Net Ecosystem Exchange (NEE) of carbon dioxide. The global process-based biosphere model ORCHIDEE used in this study showed that a standard model parameterization produces seasonal NEE patterns that are opposite in phase to the eddy flux data of the Tropical evergreen Forest at the Tapajós km 67 site (Brazil), like many other global models. However, we optimized several key parameters of ORCHIDEE using eddy covariance data of the Tapajós km 67 site in order to identify the driving factors of the seasonal variations in CO2 flux in this Tropical Forest Ecosystem. The validity of the retrieved parameter values was evaluated for two other flux tower sites in the Amazon. The different tested optimization scenarios showed that only a few parameters substantially improve the fit to NEE and latent heat (LE) data. Our results confirm that these Forests have the ability to maintain high transpiration and photosynthesis during the dry season in association with a large soil depth (Dsoil = 10 m) and a rooting system density that decreases almost linearly with depth (Hroot = 0.1). Previous analyses of seasonal variations in eddy covariance fluxes indicated that higher GPP levels were reached in the dry season compared to the wet season. Our optimization analysis suggests that this pattern could be caused by a leaf flush at the start of the dry season increasing the photosynthetic capacity of the canopy. Nevertheless, the current model structure is not yet able to simulate such a leaf flush and we therefore suggest improving the ORCHIDEE model by including a specific phenology module that is driven by light availability for the Tropical evergreen PFT. In addition, our results highlight both the potential and the limitations of flux data to improve global terrestrial models. Several parameters were not identifiable and the risk of over-fitting of the model was illustrated. Nevertheless, we conclude that these models can be improved substantially by assimilating site level flux data over the tropics.
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Seasonal patterns of CO 2 fluxes in Amazon Forests: Fusion of eddy covariance data and the ORCHIDEE model
Journal of Geophysical Research, 2011Co-Authors: Hans Verbeeck, Philippe Peylin, Cédric Bacour, Damien Bonal, Kathy Steppe, Philippe CiaisAbstract:[1] In some regions of the Amazon, global biogeophysical models have difficulties in reproducing measured seasonal patterns of net Ecosystem exchange (NEE) of carbon dioxide. The global process-based biosphere model Organizing Carbon and Hydrology in Dynamic Ecosystems (ORCHIDEE) used in this study showed that a standard model parameterization produces seasonal NEE patterns that are opposite in phase to the eddy flux data of the Tropical evergreen Forest at the Tapajós km 67 site (Brazil), like many other global models. However, we optimized several key parameters of ORCHIDEE using eddy covariance data of the Tapajós km 67 site in order to identify the driving factors of the seasonal variations in CO 2 flux in this Tropical Forest Ecosystem. The validity of the retrieved parameter values was evaluated for two other flux tower sites in the Amazon. The different tested optimization scenarios showed that only a few parameters substantially improve the fit to NEE and latent heat data. Our results confirm that these Forests have the ability to maintain high transpiration and photosynthesis during the dry season in association with a large soil depth (D soil = 10 m) and a rooting system density that decreases almost linearly with depth (H root = 0.1). Previous analyses of seasonal variations in eddy covariance fluxes indicated that higher GPP levels were reached in the dry season compared to the wet season. Our optimization analysis suggests that this pattern could be caused by a leaf flush at the start of the dry season increasing the photosynthetic capacity of the canopy. Nevertheless, the current model structure is not yet able to simulate such a leaf flush, and we therefore suggest improving the ORCHIDEE model by including a specific phenology module that is driven by light availability for the Tropical evergreen plant functional types. In addition, our results highlight both the potential and the limitations of flux data to improve global terrestrial models. Several parameters were not identifiable, and the risk of overfitting of the model was illustrated. Nevertheless, we conclude that these models can be improved substantially by assimilating site level flux data over the tropics.
Amilcare Porporato - One of the best experts on this subject based on the ideXlab platform.
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Optimal management of cattle grazing in a seasonally dry Tropical Forest Ecosystem under rainfall fluctuations
Journal of Hydrology, 2020Co-Authors: Rodolfo Marcondes Silva Souza, Samantha Hartzell, Xue Feng, Antonio Celso Dantas Antonino, Eduardo Soares De Souza, Rômulo Menezes, Amilcare PorporatoAbstract:Abstract Climate change will likely trigger shifts in rainfall regimes that may intensify water scarcity in semi-arid regions. In the semi-arid region of Brazil, the seasonally dry Ecosystem is the primary source of forage for livestock. Because the correct stocking rate of livestock (animals per area) is not well understood, overgrazing tends to advance rangeland degradation in this Ecosystem. This implies that the region may become even more vulnerable under changing rainfall regimes, which in turn may exacerbate livestock and food insecurity. We developed a coupled soil water balance, vegetation, and cattle biomass model to illustrate the impacts of rainfall seasonality on the dynamics of vegetation and animal growth. The outcomes were simulated by considering different stocking rates and the timing of animal placement and removal from the rangeland. A more pronounced reduction in vegetation biomass was found in grazed vs. non-grazed paddocks. Under strongly seasonal rainfall patterns, the maximum animal weight gain decreases with average rainfall inter-arrival time and increases with total annual rainfall. Thus, a forecast of dry spells could benefit farmers in planning grazing management strategies. Our model can be used to test different management scenarios and give feedback for local herders, and to guide future experiments to reduce the time and cost of acquiring data.
P A Verweij - One of the best experts on this subject based on the ideXlab platform.
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shedding light on relationships between plant diversity and Tropical Forest Ecosystem services across spatial scales and plot sizes
Ecosystem services, 2020Co-Authors: Gijs Steur, R W Verburg, M J Wassen, P A VerweijAbstract:Abstract This paper sheds light on the state of our knowledge of relationships between plant diversity and Tropical Forests Ecosystem services. We systematically reviewed the empirical evidence of relationships between three Ecosystem services: carbon stock and sequestration, timber provisioning and non-timber Forest product (NTFP) provisioning, and three dimensions of plant diversity: taxonomic, functional and structural. We carried out meta-analyses to assess their validity across spatial scales and plot sizes. We found that indicators of all three dimensions of plant diversity have reported relationships with at least two of the studied Ecosystem services, but there has been limited and inconsistent use of plant diversity indicators and little attention for relationships with timber and NTFP services. Nevertheless, we found that tree species richness showed robust significant positive correlations with carbon stock across the tropics, and that the geographical extent of the study area had a significant negative effect on the strength of this relationship, where the strength of the relationship decreased with increasing geographical extent. This paper reveals a knowledge gap for services other than carbon stock and shows that at local to regional spatial scales, synergies can be achieved between policies focused on biodiversity conservation and maintenance of carbon stocks.
Royd Vinya - One of the best experts on this subject based on the ideXlab platform.
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Seasonal changes in plant-water relations influence patterns of leaf display in Miombo woodlands: evidence of water conservative strategies.
Tree Physiology, 2018Co-Authors: Royd Vinya, Nick D. Brown, Joshua B Fisher, Yadvinder Malhi, Timothy J Brodribb, Luiz Eduardo Oliveira E.cruz De AragãoAbstract:Water availability has frequently been linked to seasonal leaf display in seasonally dry Ecosystems, but there have been few ecohydrological investigations of this link. Miombo woodland is a dominant seasonally dry Tropical Forest Ecosystem type in southern Africa; however, there are few data on the relationship between seasonal dynamics in plant–water relations and patterns of leaf display for Miombo woodland. Here we investigate this relationship among nine key Miombo woodland tree species differing in drought tolerance ability and leaf phenology. Results of this study showed that seasonal patterns of leaf phenology varied significantly with seasonal changes in stem water relations among the nine species. Leaf shedding coincided with the attainment of seasonal minimum stem water potential. Leaf flush occurred following xylem rehydration at the peak of the dry season suggesting that endogenous plant factors play a pivotal role in seasonal leaf display in this Forest type. Drought-tolerant deciduous species suffered significantly higher seasonal losses in xylem hydraulic conductivity than the drought-intolerant semi-evergreen tree species (P < 0.05). There was a significant and positive correlation between species drought tolerance index and species’ seasonal loss in hydraulic conductivity (P < 0.05), confirming the ecological role of long-distance xylem transport in this seasonally dry Tropical Forest. Our results reveal that water stress in seasonally dry Tropical Forests selects for water conservative traits that protect the vulnerable xylem transport system. Therefore, seasonal rhythms in xylem transport dictate patterns of leaf display in seasonally dry Tropical Forests.