Ecophysiological Models of Forest Stand Dynamics

It is well known that woodlands play a crucial role in stabilizing the natural environment. They greatly influence and regulate hydraulic cycles, and thus the flow of waters and local humidity conditions. They also filter air pollutants, thus protecting vulnerable soils and water bodies within forested watersheds. Therefore, as global belts of Boreal, Moderate and Tropical Forests actively take part in different biogeochemical and physical cycles in the biosphere, and play an extremely important role in the exchange of heat and moisture between the atmosphere and continents, an assessment of the forests in different time and spatial scales is of considerable value to the life of the human society. The systems approach permits us to look at these interrelationships in a comprehensive way and to see many negative and positive feedbacks which, together, provide a dynamical equilibrium of the waves in the all forest belts mentioned above (including others organic and inorganic waves, such as waves of insects, diseases, fires etc.). In the course of its existence IlASA has constantly been occupied with different aspects of the forest life. From time to time international working groups are formed on a IlASA base to examine the different aspects of the forest and forestry dynamics. The most recent example is a book on systems analysis of the Boreal Forest Dynamics, published by Cambridge University Press (Shugart et al., eds., September 1991). A group of American, European, Canadian and Soviet authors have worked together through a collaborative network. The products of the group include a general boreal forest model (which is currently being used to evaluate the potential effects of global climate change on the North American Boreal Zone); models on fire dynamics, seed dispersal, permafrost dynamics, herbivory and CO2 flux have been developed, providing a general modeling framework for simulating patterns and processes in the boreal zone. The present paper may be considered as some additional input to the problem, in the form of Ecophysiological Models, which were partially missing in the above-mentioned book. The paper partially intersects with the contents of the book, but from a different angle, especially as many papers considering the Russian view of the problem are added. The book on "System Analysis of the Boreal Forest Dynamics" and this outline stress the necessity of the development of a collaborative research effort to continue the development of computer models of the boreal forest (analogue to the GCM -- see, for example, Shugart, Bonan), and the so-called analytical models (analogue to the Global Average Models (GAM) -- see for example Antonovsky, Korzukhin) in response to environmental change. Assessments of anthropogenic stress on forests that show such complex dynamics are daunting. There is a clear need for a continuation of process-oriented comparative studies in polluted and non-polluted regions of the boreal forests to better understand these effects. It is clear from the reviews of actual observations and experimental evidence from the boreal forest and from the boreal forest models that the landscape response of boreal forests to stress is complex and not easily obtained from static measurements. Furthermore, the feedback complexities in the boreal forest ecosystem suggest that a multiple research program of experimentation, modeling and observation may lead to a better understanding of the forest dynamics under stress or novel situations than one-dimensional research programs