Simulating carbon and water flows and growth in a Mediterranean evergreen Quercus ilex coppice using the FOREST-BGC model

Abstract

The process-based model FOREST-BGC calculates the flow of water, carbon and nitrogen through forest ecosystems. This model, originally developed for conifer species, has been adapted to a Mediterranean evergreen oak species: Quercus ilex. This application requires species specific parameters and modification of the model. First, we attempted to reproduce the level of drought stress experienced by the holm oak using a new relationship between soil water content and soil water potential. Second, to take into account the coppice structure of these ecosystems and the small stem diameter, we assumed that all the woody biomass was respiring. A 50-year simulation was performed for the homogeneous ecosystem at the Puéchabon site, southern France. Water and carbon flows and biomass were examined for the last period, 1984–1993. Simulated values were compared with (1) measured soil water content and predawn leaf water potential from 1984 to 1986, (2) wood annual radial growth recorded since 1984, and (3) standing biomass estimated at the Puéchabon site. The simulated predawn leaf water potential decreased in summer and reached −3.9 MPa in 1985. For the 1984–1993 period, mean ecosystem transpiration was 363 mm per year for a leaf area index of 2.9. The mean annual gross primary production was 1354 g C m −2 soil. Simulated mean annual carbon allocated to aboveground wood was 85 g C m −2 soil. In 1993, the simulated aboveground biomass of the ecosystem was 3275 g C m −2 soil for wood and 252 g C m −2 soil for leaves. These simulation results are in agreement with field measurements on the Puéchabon site and on similar ecosystems in the Mediterranean region. They reproduced the intra-annual effects of the drought stress on holm oak. These results show that the FOREST-BGC model can be used for modeling the function and growth of Mediterranean oak coppice.