Could ecophysiological traits and related ecohydrological processes explain competition and succession trend in warm-temperate broadleaved forests?

Competition between birch and oak in warm-temperate broadleaved forests is intense and very important in evaluating carbon and water balance at landscape and regional scales. Ecosystem biogeochemical model (Terrestrial Ecosystem Simulator) is applied to warm-temperate broadleaved forests in Donglingshan Watershed in Beijing area to simulate NPP, NEP, carbon fixing capacity, erosion, and their responses to climate change. In particular, we are interesting in whether the TESim model considering plant ecophysiological traits and related ecohydrological processes can explain competition between birch and oak and succession trend to some degree in this area. Ecophysiological parameters were parameterized using field leaf-gas-exchange measurements by Licor 6400 of dominant species and field sampling on plant and soil nutrients, soil water and texture in the summer of 2006. Model is then validated by long-term forests inventory data and intensive on-site monitoring and studies of the CERN (Chinese Ecosystem Research Network) field station located in the watershed. The results indicated that the simulated stem-branch biomass, leaf biomass, NPP, ecosystem respiration, and littering matched pretty well with long time on-site measurements and studies. Because of higher dependency on soil water and carbon assimilation rate, white birch maintained higher growth rate and thus dominant at the early succession stage. When competition on soil water became intense, oak could maintain a higher growth rate in the middle of the succession because of its drought tolerance capacity. At the late succession stage, birch declined because of more severe water stress and light stress due to dominance by oak.