Simulation of the vegetation structure and function in a Malaysian tropical rain forest using an individual-based dynamic vegetation model

Background/Question/Methods Tropical forests play an important role in the global carbon balance; these systems comprise approximately one-half of total terrestrial production and global terrestrial biomass. On the other hand, tropical forests contain at least two-thirds of the world's biodiversity. Hence, it is critical to develop a model that simulates how the structure, function, and biodiversity of tropical forests respond to rising atmospheric CO2 and resulting climatic changes. During the past decade, German researchers have developed a gap dynamics model FORMIX3 for a tropical rain forest in Malaysia, and have simulated tree dynamics by considering growth, competition, regeneration, mortality, and gap formation. In the model, the growth process is based on dry matter production; thus, it incorporates interactions between tree dynamics and carbon balances. Although FORMIX3 reconstructs forest structure, successional patterns, and carbon balance in a Malaysian tropical rain forest, the model is only based on empirical relationships under current environment conditions and therefore does not help to explain how results will be modified by changes in climate and atmospheric CO2.

Results/Conclusions By incorporating formulas and parameters from the FORMIX3, I adapted an individual-based Dynamic Global Vegetation Model, SEIB-DGVM to a Malaysian tropical rain forest. After calibration, the model reconstructed forest structure (i.e., size structure, leaf area index, and woody biomass) and carbon fluxes (i.e., gross and net primary productivity) of a dipterocarp forest in Pasoh, Peninsular Malaysia. Sensitivity analysis demonstrated that the model was robust; forest structure and ecosystem functions moderately fluctuated due to changes in parameters and climatic environments. Sensitivity analysis also indicated that the success and decay of a dominant species group that monopolized the canopy layer greatly affected those of a less-abundant, shade-intolerant group. This result indicates that even if environmental changes do not exhibit clear effects on dominant canopy species and/or whole forest structure, such changes may still substantially impact the biodiversity of subdominant species.