MODELING DYNAMIC VEGETATION RESPONSE TO RAPID CLIMATE-CHANGE USING BIOCLIMATIC CLASSIFICATION

Modeling potential global redistribution of terrestrial vegetation fre quently is based on bioclimatic classifications which relate static re gional vegetation zones (biomes) to a set of static climate parameters . The equilibrium character of the relationships limits our confidence in their application to scenarios of rapidly changing climate. Such a ssessments could be improved if vegetation migration and succession wo uld be incorporated as response variables in model simulations. We dev eloped the model MOVE (Migration Of VEgetation), to simulate the geogr aphical implications of different rates of plant extirpation and in-mi gration. We used the model to study the potential impact on terrestria l carbon stocks of climate shifts hypothesized from a doubling of atmo spheric greenhouse gas concentration. The model indicates that the ter restrial vegetation and soil could release carbon; the amount of this carbon pulse depends on the rate of migration relative to the rate of climate change. New temperate and boreal biomes, not found on the land scape today, increase rapidly in area during the first 100 years of si mulated response to climate change. Their presence for several centuri es and their gradual disappearance after the climate ceases to change adds uncertainty in calculating future terrestrial carbon fluxes.