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Research Interests:
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Research Interests:
Water availability is the main factor limiting ecosystem productivity in Mediterranean ecosystems, and is expected to increase as a result of climate change in the Mediterranean region. Hence, understanding and anticipating the effect of... more
Water availability is the main factor limiting ecosystem productivity in Mediterranean ecosystems, and is expected to increase as a result of climate change in the Mediterranean region. Hence, understanding and anticipating the effect of water limitation on those ecosystems is of most importance for future generations. The Puechabon experimental site, located in southern France, is representative of typical Mediterranean forests, dominated by Quercus ilex. This site has been monitored at levels from leaf to ecosystem since 1984, including eddy correlation measurements since 1998 and a partial throughfall interception experiment since 2003. With this contribution, we focused on developing, calibrating and validating a process-based model (CASTANEA, Dufrêne et al., 2005) on the Puechabon site, for simulating the effect of the throughfall interception on stand gross (GPP) and net (NPP) primary productivity. Model developments at the seasonal scale included detailed representations of leaf demography and wood growth seasonal dynamics, based on detailed monitoring of leaf litter (26-year time series) and cambium dynamics (7-year time series), respectively. New biomass compartments (flowers and fruits) were developed and implemented to the original vegetative carbon module, and helped insuring a realistic representation of woody vegetative pools dynamics (as fructification can require on a given year up to 15% NPP) along the 26-year growth time series. Once improved, the model allowed us to assess the influence of water stress on leaf demography (positive covariation of leaf lifespan and drought duration) and on carbon allocation at tree level (negative covariation of leaf area with drought), based on a comparison between the control site (where the model was developed and validated) and the 6-year partial throughfall exclusion. Keywords: Quercus ilex, process-based modeling, net primary production, carbon allocation, fructification, throughfall exclusion
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We studied monoterpene emissions from the evergreen oak Quercus ilex exposed to different levels of summer drought to examine the seasonal variation of emissions in the Mediterranean area and to test the role of water limitations therein.... more
We studied monoterpene emissions from the evergreen oak Quercus ilex exposed to different levels of summer drought to examine the seasonal variation of emissions in the Mediterranean area and to test the role of water limitations therein. Measurements were made in seven campaigns between June and January on intact leaves of mature trees growing in two adjacent sites, in one of which the natural water supply was reduced by a ground roof. In both sites, actual emission rates as well as light- and temperature-normalized emission rates (i.e., emission factor (EF)) significantly changed during the seasons: Mean EFs increased from June to July to a broad summer maximum between 5.2 and 9.4 nmol m-2 leaf area s-1 (12-21 μg g-1 leaf dry mass h-1), dropped in October and November and reached a minimum of about 0.77 nmol m-2 s-1 (1.7 μg g-1 h-1) in January. From June to July, mean EFs of the trees with reduced water supply were significantly lower than those of trees with normal water supply. The lowered EF in summer was paralleled by lower predawn water potentials, leaf transpiration, photosynthesis and stomatal conductance with respect to control trees. The results suggest that in natural Q. ilex habitats the seasonal evolution of EF follows a marked summer-winter cycle whose shape and intensity can be modified by summer drought.
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Research Interests:
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Pourquoi étudier les effets de changements climatiques sur les écosystèmes méditerranéens? Le doublement du CO2 atmosphérique pour les années 2030-2050 est maintenant admis. Ce doublement est en train d'affecter le climat du globe et... more
Pourquoi étudier les effets de changements climatiques sur les écosystèmes méditerranéens? Le doublement du CO2 atmosphérique pour les années 2030-2050 est maintenant admis. Ce doublement est en train d'affecter le climat du globe et d'influer sur ...
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The effects of climate changes on carbon and water fluxes are quantified using a physiologically multi-layer, process-based model containing a carbon allocation model and coupled with a soil model (CASTANEA). The model is first evaluated... more
The effects of climate changes on carbon and water fluxes are quantified using a physiologically multi-layer, process-based model containing a carbon allocation model and coupled with a soil model (CASTANEA). The model is first evaluated on four EUROFLUX sites using eddy covariance data, which provide estimates of carbon and water fluxes at the ecosystem scale. It correctly reproduces the diurnal fluxes and the seasonal pattern. Thereafter simulations were conducted on six French forest ecosystems representative of three climatic areas (oceanic, continental and Mediterranean areas) dominated by deciduous species (Fagus sylvatica, Quercus robur), coniferous species (Pinus pinaster, Pinus sylvestris) or sclerophyllous evergreen species (Quercus ilex). The model is driven by the results of a meteorological model (ARPEGE) following the B2 scenario of IPCC. From 1960 to 2100, the average temperature increases by 3.1 °C (30%) and the rainfall during summer decreases by 68 mm (−27%). For all the sites, between the two periods, the simulations predict on average a gross primary production (GPP) increase of 513 g(C) m−2 (+38%). This increase is relatively steep until 2020, followed by a slowing down of the GPP rise due to an increase of the effect of water stress. Contrary to GPP, the ecosystem respiration (Reco) raises at a constant rate (350 g(C) m−2 i.e. 31% from 1960 to 2100). The dynamics of the net ecosystem productivity (GPP minus Reco) is the consequence of the effect on both GPP and Reco and differs per site. The ecosystems always remain carbon sinks; however the sink strength globally decreases for coniferous (−8%), increases for sclerophyllous evergreen (+34%) and strongly increases for deciduous forest (+67%) that largely benefits by the lengthening of the foliated period. The separately quantified effects of the main variables (temperature, length of foliated season, CO2 fertilization, drought effect), show that the magnitude of these effects depends on the species and the climatic zone.