DECOMPOSITION PROCESSES - MODELING APPROACHES AND APPLICATIONS

Decomposition is a fundamental ecosystem process, strongly influencing ecosystem dynamics through the release of organically bound nutrients . Decomposition is also a complex phenomenon that can be modified by c hanges in the characteristics of the decaying materials or prevailing environmental conditions. For these reasons, the impacts of local, reg ional or global environmental changes on the quality and turnover of d ead organic matter are of considerable interest. However, realistic li mits to the complexity, as well as temporal and spatial scales, of exp erimental studies restrict their usefulness in extrapolating long-term or large-scale results of simultaneous environmental changes. Alterna tively, many simulation models have been constructed to gain insight t o potential impacts of anthropogenic activities. Because structure and approach determine the strengths and limitations of a model, they mus t be considered when applying one to a problem or otherwise interpreti ng model behaviour. There are two basically different types of models: (1) empirical models generally ignore underlying processes when descr ibing system behaviour, while (2) mechanistic models reproduce system behaviour by simulating underlying processes. The former models are us ually accurate within the range of conditions for which they are const ructed but tend to be unreliable when extended beyond these limits. In contrast, application of a mechanistic model to novel conditions assu mes only that the underlying mechanisms behave in a consistent manner. In this paper, we examine models developed at different levels of res olution to simulate various aspects of decomposition and nutrient cycl ing and how they have been used to assess potential impacts of environ mental changes on terrestrial ecosystems.