The Integration of Vegetation Dynamics into a Multi-layer Higher-order closure Land Surface Model

The changes in global climate are known to have impacts on ecosystem structure, and such structural changes may in turn impact the global climate through a series of complex feedback mechanisms. The UC Davis Advanced Canopy Atmosphere Soil Algorithm (ACASA) that utilizes higher-order closure turbulent transport between 10 layers within a canopy and 10 layers above, coupled with full plant physiological parameterizations, snow hydrology, and a three-stream radiation model, was used to simulate the biogeophysical processes, and the dynamic vegetation model adapted from the Community Land Model (CLM-DGVM) was used to estimate the structural evolution of the ecosystem. To quantitatively investigate the impacts of the nonlinear feedback mechanisms between the climate system and ecosystems, simulation results between ACASA with and without CLM-DGVM were carefully compared with each other. The numerical simulations were driven by selected AmeriFlux site observations from 1992 to 2008, encompassing a deciduous broadleaf forest in Massachusetts, an evergreen needleleaf forest in North Carolina, and a grassland in Arizona. ACASA was able to reasonably simulate the general behavior of the tested ecosystem types, and the simulated evapotranspiration tends to be sensitive to plant phenology and canopy architecture in addition to physiologically controlled plant assimilation processes. These results suggest that the coupling between land surface models and dynamic vegetation models is needed to increase our understanding of regional and global climate change and the associated impacts on ecosystem structure.