Introduction

In this chapter we present various models of timber production for the two species under consideration: Sitka spruce and beech. In the next section we present a brief review of previous studies. These have exclusively been based upon relatively small-scale surveys of tree growth; furthermore, they have also generally been confined to comparatively small areas and often to one topographic region, e.g. upland areas. Our study differs from these previous models in that it employs a GIS to utilise large-scale existing databases covering a very large and diverse study area: the whole of Wales. The subsequent section presents details regarding the various datasets used in this study and discusses how these data were transformed for the purposes of subsequent regression analysis. Subsequently, results from our models of Sitka spruce and beech growth rates are presented, while the following section presents and analyses GIS-created map images of predicted yield class. The final section applies the findings of the previous chapter to produce monetised equivalents of these results.

Literature review and methodological overview

Literature review

It is clear that tree growth rates depend upon a variety of species, environmental and silvicultural factors. Early work in this field relied on simple rules of thumb based upon relatively little supporting data (Busby, 1974) or analyses of single factors. Reviews across this literature provide a number of clues regarding the specification of a yield class model. An early focus of interest was the impact of elevation upon productivity (Malcolm, 1970; Mayhead, 1973; Blyth, 1974).