THE PREDICTION AND DISTRIBUTION OF GENERAL YIELD CLASSES OF SITKA SPRUCE IN SCOTLAND BY EMPIRICAL-ANALYSIS OF SITE FACTORS USING A GEOGRAPHIC INFORMATION-SYSTEM

A framework has been developed to predict growth of Sitka spruce (Picea sitchensis (Bong.) Carr.) at a regional scale throughout Scotland based on an analysis of yield, site, and climatic factors. Using the general yield class (GYC) system for predicting forest production (m(3) ha(-1).year(-1)), the statistical model was integrated with a geographic information system to predict tree growth at a resolution of 1 km(2) Site factor data from 487 sample sites were analysed along with the associated climate data derived from monthly 30-year means recorded at meteorological stations throughout the country. Multiple regression was used to develop and validate the model, which accounted for 59% of the variation in observed GYC. Standard errors of prediction were determined by analysis of variance to provide confidence limits for the 1-km(2) GYC predictions. The distribution of these estimates of production was plotted in the form of a digital map for Scotland, housed within the geographic information system and providing a facility to readily analyse and summarise regional information.