Suitability of process-based tree growth models for addressing tree response to climate change

Empirical models of tree growth have been used for many years to predict ti mber yields and other properties of trees. However, such models rely on mea sured relationships between tree growth and historic environmental conditio ns. As anthropogenic actions alter the environment, especially atmospheric composition, empirical models become less reliable and process-based models become more useful. Process-based models are challenged to simulate growth of structurally and physiologically complex organisms using explicit mathe matical expressions to capture growth response to environmental conditions. In this review we summarize the physiological requirements of process-base d models and examine the capabilities of six published models (CARBON, ECOP HYS, PGSM, TREE-BGC, TREGRO, W91) for simulating tree response to changes i n environmental conditions (elevated temperature, increased CO2 concentrati on, and enhanced concentrations of tropospheric ozone). These analyses indi cate that current models are reliable integrators of environmental effects on individual processes (e.g. photosynthesis), but may be less reliable whe re physiological acclimation occurs or when extrapolated to growth of speci fic tree compartments. (C) 2000 Elsevier Science Ltd. All rights reserved.