USING ECOSYSTEM MODELS TO PREDICT REGIONAL CO2 EXCHANGE BETWEEN THE ATMOSPHERE AND THE TERRESTRIAL BIOSPHERE

Ecologically sound models of the terrestrial biosphere are needed in the investigation of the Earth system and global change. Traditional ecosystem models simulate many processes and dynamics relevant to the functioning of the Earth system, but their application is limited by their local, small-scale, often site-specific nature. We address this limitation by deriving a method for predicting regional biosphere dynamics by extrapolation from smaller-scale ecosystem models. We use models of local ecosystem carbon dynamics to predict the seasonal exchange of CO2 between the atmosphere and terrestrial ecosystems of 64 degrees N to 90 degrees N latitude. Monte Carlo simulation is used to integrate solutions of a tundra model and a coniferous forest model across within-biome heterogeneity in the models' climatic driving variables. The product of the expected value of each model's output and the area of the region occupied by that biome or ecosystem type is an estimate of biome-scale CO2 exchange. Regional CO2 exchange is the sum of the biome exchanges. Comparisons of the extrapolation's results with independent estimates of seasonal CO2 exchange and annual net primary production support the proposition that extrapolation of ecosystem models can be used to simulate regional biosphere dynamics.