TESTING THE RESPONSES OF A DYNAMIC GLOBAL VEGETATION MODEL TO ENVIRONMENTAL-CHANGE - A COMPARISON OF OBSERVATIONS AND PREDICTIONS

Dynamic global vegetation - biogeochemistry models are required to pre dict the likely responses of the terrestrial biosphere to anticipated future global environmental change and for improved representation of an active vegetation surface within general circulation models of the Earth's global climate system. Testing the predictions of such models is essential to their development prior to use in a predictive capacit y. The climate change experiment (CLIMEX) has exposed an entire catchm ent of boreal vegetation to elevated CO2 (560 ppmv) and temperature (3 degrees C in summer, +5 degrees C in winter) for the past three year s and has a considerable archive of pre-and posttreatment measurements of both CO2 and water vapour fluxes of the vegetation, catchment runo ff and soil nutrient status. These data have been used to test the pre dictions of the University of Sheffield dynamic global vegetation mode l (SDGVM) for the same site using historical records of climate as inp ut. Comparisons of observations and predictions at the scale of indivi dual leaves and whole ecosystems are generally favourable, increasing our confidence in the application of the model to forecasting the resp onses of the terrestrial biosphere to various global change scenarios. The SDGVM has been used to predict the future responses of the ecosys tem at the site into the year 2003AD. The results indicate rather smal l changes in leaf area index and catchment runoff but quite large incr eases in net primary productivity. The model predictions are now open to testing further as the CO2 and temperature treatments continue in t he CLIMEX greenhouse.