DEVELOPMENT OF GROWTH-MODELS FOR PINUS-RADIATA IN NEW-ZEALAND - EXPERIENCE WITH MANAGEMENT AND PROCESS MODELS

The Forest Research Institute (FRI) has recently finished developing a series of management growth models for Pinus radiata within major bio -geo-climatic regions. These are stand-level models consisting of a se ries of stochastic differential equations, with the state of the stand at any one time being described by the major variables of top height, basal area and number of stems per hectare. Additional state variable s and time-scale multipliers are used to account for regional differen ces in patterns of growth, loss of site occupancy, nitrogen and phosph ate fertiliser effects, and increased growth due to improved breeds of trees. The research programme has been driven by the forest manager's need to accurately regulate yield in a period with a greater demand t han supply, and to evaluate the profitability of new afforestation. It was necessary to predict the response to extremes of silvicultural re gimes, ranging from dense pulpwood to widely spaced, high pruned stand s. From 1986 onwards, an FRI/Industry Stand Growth Model Cooperative h as facilitated data collection, research and technology transfer. Sinc e the early 1980s, a research programme to construct process models fo r Pinus radiata has contributed to understanding physiological process es, particularly water balance and interception of solar radiation. Ho wever, initial expectations that such models would contribute to impro vements in forest management, or to better management growth models ha ve so far not been met. There is no