LANDSCAPE TO REGIONAL-SCALE RESPONSES OF TERRESTRIAL ECOSYSTEMS TO GLOBAL CHANGE

The Global Change and Terrestrial Ecosystems (GCTE) project has twin o bjectives: to predict the feedback effects of changes in terrestrial e cosystems on the atmosphere and climate; and, at a finer scale, the ef fects of global changes on the structure and function of natural and a gro-ecosystems. The main feedback effects are via exchanges of energy, water and momentum, and changes in biogeochemistry. All these process es are affected by ecosystem composition; to obtain a quantitative und erstanding of the interactions involved, it is necessary to describe v egetation in terms of its functional characteristics, based on a gener ally applicable classification of plant functional types (PFTs). Globa l-scale simulations of induced changes in ecosystem composition have p rogressed from non-dynamic, top-down models to mechanistic, ecophysiol ogical models that predict PFTs and leaf-area index or biomass using p lant responses to environmental conditions. Two such models are now be ing incorporated into general circulation models (GCMs), as first atte mpts at coupled atmosphere-biosphere models. Parallel developments inc lude global-scale process models, which use fixed vegetation types to predict net primary production and nitrogen cycling, and a bottom-up m odelling approach. The latter begins with detailed, mechanistic patch- scale models, extending to spatially variable versions involving lands cape processes and gradually incorporating simplifying routines to all ow for large data sets. The many implications of global change for agr iculture are illustrated by two examples: cereal crop-effects; and pes ts and diseases.