INTRODUCTION 



What are the future impacts of present management practices on tree growth? The 

 answers to this question, for a variety of timber- growing sites and stand structures , 

 encompass the full range of skills of the silviculturist . Answering the question in 

 quantitative terms also requires the means to accomplish the large volume of computa- 

 tions that are necessary to represent the complex biological interactions that charac- 

 terize the development of a forest community. This paper describes a set of computer 

 programs for combining our current silvicultural knowledge with past growth data fr 

 a sample stjmd to make a prognosis of the course of development that the forest stand 

 is expected to follow under alternative management prescriptions. This model is 

 deliberately termed a prognosis rather than either a simulation or projection. Most 

 forest stand simulators begin with hypothetical distributions of trees in space; 

 whereas this program begins with a diagnostic description of the present forest. The 

 result is not a projection because the course of stand development depends on the 

 detailed interaction of growth factors rather than upon following an initial trajectory 

 implied by current growth rates. 



For many of our forest types, our ecological and silvicultural knowledge is 

 incomplete. It follows that the programs that comprise this model are also incom- 

 plete. My hope is that the design is sufficiently flexible that new capabilities can 

 be added as silviculturists develop better quantitative representations of the various 

 biological aspects of tree growth. Indeed, the gaps in this model call attention to 

 corresponding gaps in silvicultural research. 



An important design criterion of this model is that the prognosis should apply 

 to stands containing any mixture of species or age and size classes that grow as a 

 community. That is, the model should apply equally well to pure even-aged stands or 

 stands composed of a mixture of ages, species, and sizes. 



Growth models that are tree-by-tree analogs of stand development can be useful 

 adjuncts to silvicultural research. In this context, they can be used to interpolate 

 among the limited number of treatment combinations that can be installed in a research 

 study of feasible scope. For this use, resolution of the model should be capable of 

 describing tree growth in sufficient detail to demonstrate subtle differences between 

 treatments. On the other hand, in the context of forest management planning, much 

 less detail is required about individual trees. Consequently, the development of this 

 program has followed a middle course between the growth simulation models (described 



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