PREDICTING SITKA SPRUCE YIELDS IN THE BUCHAN AREA OF NORTHEAST SCOTLAND

Investigations were carried out into the effects of site characteristi cs on the growth rate of Sitka spruce (Picea sitchensis (Bong.) (Carr. ), in the Buchan area of north-east Scotland, using General Yield Clas s (GYC) as a site index. The degree of correlation between GYC and Lan d Classification for Forestry (LCF) class was also investigated. Data collected from 90 temporary sample plots were analysed using Principal Components Analysis and stepwise multiple regression. A model was con structed which accounted for 44.9 per cent of variation in GYC, with a n f statistic significant at the 1 per cent level. For a 95 per cent c onfidence interval, any single new prediction made by the model should be within +/-3.6 m3 ha-1 yr-1 of the true value. Validation using ind ependent data from a further 10 temporary sample plots gave a mean dif ference between observed and expected values of only 0.25 m3 ha-1 yr-1 . No significant difference was found between the means of GYC recorde d from plots on LCF classes 4, 5 and 6. The results of the study could be used to support the process of conversion of agricultural land to conifer plantation, and are pertinent to the development of more proac tive policies by local authorities towards consultative rural developm ent planning procedures.