MODELING VEGETATION STRUCTURE ECOSYSTEM PROCESS INTERACTIONS ACROSS SITES AND ECOSYSTEMS

We describe an approach to investigating and understanding the interac tions between vegetation structure and ecosystem processes that uses s imulation models as a framework for comparison and synthesis across ec osystems arrayed along environmental gradients. The models are individ ual-based vegetation simulators and compartment models of nutrient cyc ling and soil water relations. Applications focus on interactions and feedbacks between vegetation structure (species composition, size stru cture) and ecosystem processes (water balance, nutrient cycling), and how these relationships vary across environmental gradients. Prelimina ry results indicate that life-history traits of plants have a profound influence on system-level behaviors, and that differences between gra sslands and forests can be attributed largely to contrasting traits of grasses and trees. Experiments with linked vegetation-ecosystem proce ss models diverge from simulations with either model run independently , suggesting the importance of feedbacks between details of vegetation pattern and ecosystem processes. The development of a fully coupled v egetation-ecosystem process model that is sufficiently general to simu late systems dominated by multiple lifeforms presents several conceptu al, logistical, and scaling challenges, but also provides for new oppo rtunities in ecosystem theory.