Vegetatio 86: 1-13, 1990. © 1990 Kluwer Academic Publishers. Printed in Belgium l Evaluating performance of an Appalachian oak forest dynamics model Elizabeth A. Harrison I & Herman H. Shugart Department of Environmental Sciences, University of Virginia, Clark Hall, Charlottesville, VA, 22903, USA; ~Current address: Department of Geology, Michigan Technological University, Houghton, MI 49931, USA Accepted 14.2.1989 Keywords: Biological model, Biomass, Model testing, Parameterization, Simulation model Abstract An Appalachian-oak forest in a small montane watershed was sampled to calibrate and test an existing forest dynamics simulation model. Indices developed in earlier studies by Whittaker were used to estimate the response of different tree species to soil moisture. As is the case in many forest modeling applications, neither detailed environmental data at a micro-spatial scale nor quantitative historical stand data were available for the study. A protocol of both model parameter estimation and simulation output evaluation is developed. The method involves simulation experiments under which the model parameters are allowed to vary systemati- cally with respect to environmental control variables, allowing one to generate a field of potential simulation results that can be searched for patterns shared by the observed data. The degree to which common patterns emerge provides a measure of model sensitivity to patterns at the scale of interest. This protocol can provide an appraisal of the appropriateness of a simulation model to the system of interest and can be used to assess the performance of the model in future applications. Nomenclature: Little, E.B. 1971. Atlas of United States trees. Government Printing Office, Washington, D.C. Introduction Gap models (Shugart & West 1980; Shugart 1984; Dale etaL 1987) are a subclass of indi- vidual-tree-based models (Munro 1974) of forest dynamics that have been used to investigate suc- cession in natural forests. The development and testing of these models has often focused on regional-scale forest pattern (Solomon 1986; Shugart et al. 1980), and long-term (hundreds of yr) successional dynamics (Shugart 1984). In typical model tests, the average behavior of 50 to 100 of the small (ca 0.1 ha) plots simulated by the models is inspected for decade- to century- duration forest responses. In many cases the time window of application is quite long (e.g., predic- tion of old-growth forest composition, Leemans & Prentice 1987; model reconstruction of fossil pollen chronologies, Solomon 1986). There is an increasing interest in model applica- tions that involve site-specific stand projections over relatively short periods of time. These appli- cations imply use of the models at spatial and temporal scales for which they are largely