Global vegetation modeling: Plant community structure and interactions with climate change.

摘要

We are becoming increasingly aware of our impacts on the Earth's biosphere and atmosphere, but the degree and nature of future impacts and their interactions are difficult to predict. Many important components of global change revolve around global climate-vegetation interactions, particularly vegetation feedbacks to climatic change. A new Equilibrium Vegetation Ecology model (EVE) simulates natural terrestrial vegetation and is designed for interactive coupling with climate models. EVE generates a quantitative description of plant community structure, predicting fractional covers for the model's 110 plant life forms as a function of monthly mean climate. Climate is transformed into a plant community using parameterizations of dynamic ecological processes: competition for sunlight, disturbances by fire and treefall and associated secondary succession. EVE's plant life forms respond independently to climate changes, affecting the composition of each plant community, and giving them independent migrational trajectories, consistent with paleoecological data. Model sensitivity studies demonstrated that global vegetation patterns are sensitive to climate perturbations. Simulations using doubled CO₂ scenarios from five global climate models (GCMs) exhibited a decline in forests associated with their poleward migration, with a commensurate expansion of grasslands.; Two pairs of coupled EVE-GCM simulations were performed, both with 1x and 2xCO₂: one with prescribed vegetation, and the other with fully interactive vegetation. The interactive simulations used another model (LEAF) to simulate the seasonal phenology of EVE's plant canopies as a function of daily climate, providing leaf area and other physical quantities needed for coupling vegetation and climate models. Large effects of vegetation feedbacks in the interactive simulations are found at the northern and southern ecotones of the boreal forest. Poleward migration of boreal forests into tundra caused by CO₂-induced warming is enhanced by a strong forest canopy snow-masking albedo feedback. The invasion of temperate grasslands into the southern boreal forest is also enhanced due to summer warming spreading from the north. Desertification of subtropical grasslands is mostly reversed due to enhanced monsoonal precipitation. While the effect of the vegetation feedbacks on global climate averages was small, the effect on climatological zonal and regional means was significant.