Coupling global models of vegetation structure and ecosystem processes

Many currently available biogeochemical ecosystem process models capture the essential processes of trace gas fluxes between atmosphere and ecosystems, as well as the associated changes in net primary productivity. When used in climate change impact scenarios, one of the most serious limitations of these models is due to the fact that the structure of the ecosystem itself is prescribed from a global data base. Significant shifts of the major biomes of the globe are likely to occur under changed climatic conditions, and, hence, the assumption of stable ecosystem structure could fail. To overcome this problem, we have coupled an ecosystem structure model (BIOME) with a biogeochemical ecosystem process model (the Frankfurt Biosphere Model, FBM). Here we present results for high-latitude ecosystems. The coupled model has an average npp of 343.4 g C m^-2 a^-1. The application of the coupled model under a GCM based scenario of changing temperature and precipitation results in major changes of the biome boundaries at these high latitudes. The resulting average npp decreases by 8.8%. If the model is run with changed climate but unchanged biome distribution the average npp decreases by 5.4% only.