Process models of environmental systems: Simulation of forest development dynamics as an example

Successful management and stewardship of environmental systems requires reliable assessment of their development dynamics in response to changing environmental and management conditions. Descriptive (statistical) models cannot cope with this challenge since their development is based on historical time series with little or no reference to actual system structure. On the other hand, explanatory (process) models attempt to capture the essential eco-physiological processes determining dynamic behavior, and they are therefore much better suited for the computation of development dynamics under changing conditions, even when long-term empirical observations are not possible or feasible. As an example of the use of process models in environmental systems analysis, a forest simulation model describing growth, and carbon and nitrogen dynamics of a single-species, even-aged forest stand under silvicultural management and pollution influence is presented, together with some representative simulation results. Steps in obtaining valid but compact tree models for complex forest simulations are outlined, and recent software developments (object-oriented programming) are assessed with respect to their potential for evironmental systems analysis.