Terrestrial ecosystems are an important component of the global climate system. To study C balance, biophysics, and vegetation dynamics under the global change, prognostic simulations using dynamic global vegetation models are widely used. However, due to the large scale gap between local ecological dynamics and grid cells of a global model, an explicit simulation of transient forest change is challenging. Moreover, especially in forest ecosystems, the time lag between an environmental change and ecological changes are significant. To explicitly simulate the transient changes of terrestrial ecosystem properties, I modify a pre-existing individual-based forest gap model using the size- and age-structured approximation. The approximation method estimates the collective behavior of individual trees of each plant functional types categorized into several size and age classes, using a set of partial differential equations that represent ecophysiological, population, and community dynamics.
Results/Conclusions
Since the size- and age-structured dynamic global vegetation model is no longer dependent on stochasticity reproduced by random numbers, the simulated ecosystem structure (e.g., biome type and tree size) and functioning (e.g., net primary production and transpiration) followed the environmental gradient smoothly. Moreover, since the structured model simulates the forest dynamics by a set of partial differential equations, the computational time was significantly reduced. The model reasonably reproduced the current C stock (i.e., biomass and soil organic C) and flow (i.e., photosynthesis and respiration) according to a global climate database. With a dynamic coupling to a general circulation model, the model will be a powerful tool to predict the future C balance under climate change. The coupled system can also be used to effectively reproduce the transient history of the interaction between climate and terrestrial ecosystem in the past.
