Simulation of Plant Physiological Processes Using Fuzzy Variables

Qualitative modelling can help us understand and project effects of multiple stresses on trees. It is not practical to collect and correlate empirical data for all combinations of plant/environments and human/climate stresses, especially for mature trees in natural settings. Therefore, a mechanistic model was developed to describe ecophysiological processes. This model is qualitative and incorporates symbolic descriptions of important variables and their relationships. Fuzzy values, such as “zero,” “low,” “moderate,” etc., are used to express quantity and change in the model. A current application of this fuzzy variable model examines the interaction of drought and ozone stresses on a mature ponderosa pine tree. As new empirical results become available, the model can be modified to include realistic baseline values and specific mathematical relationships. Vol. 5, No. 4, 1991 Simulation of Plant Physiological Processes Using Fuzzy Variables Daniel L. Schmoldt USDA Forest Service Southeastern Forest Experiment Station Brooks Forest Products Center Virginia Polytechnic Institute and State University Blacksburg, Virginia 24061-0503 C hanges in the global environment, such as increases in air pollutants, could profoundly affect the distribution and composition of forests. Anticipated changes include increased levels of air pollutants. Early prediction of forest ecosystem responses to air pollutants is needed to provide lead time for planning (Pathak et al. 1986). If exposure-response relationships are sufficiently understood, major biological, social, and economic impacts (Crocker and Forster 1986) may be avoided by controlling establishment of new pollution sources (e.g., Fox et al. 1989) or by reducing current sources to acceptable levels. The interactions among factors that influence forest health are complex, however, and it will be difficult to predict accurately the combined effects of different stresses without understanding the underlying physical, chemical, and biological processes that operate throughout the atmosphere, plant, and soil. Ultimately, scientists and managers need to know the regional impacts of climate change and air pollutant impacts on vegetation. Before extrapolating to this level, however, it is necessary to understand how various stresses affect individual plants at 3 specific locations