Sitka Spruce (Picea sitchensis) in North-East Scotland I. Relationships between Site Factors and Growth

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Abstract
Local yield class of Sitka spruce and climatic, physiographic and soil variables were measured in seventy-three 0.01 ha plots within 12 forest blocks distributed throughout north-east Scotland. Plots were classified into three geographical groups (Northern, Deeside and Perthshire) and four elevation zones (50–150 m, 150–250 m, 250–350 m and 350–450 m). When all plots are considered together growth is positively correlated with soil temperature during the growing season and with winter rainfall. Growth is also significantly correlated with elevation, position-on-slope and topex, but not with aspect or slope. Total N of the organic layer shows the highest correlation of all site variables with growth, and, along with total P, it is the most consistently correlated variable within blocks and groups of forests. Several negative associations exist between growth and acetic and nitric acid extractable K. Within the two middle elevation zones growth on serpentine soils is significantly lower than that on soils developed from acidic parent material. For the whole region growth on major soil groups decreases in the order: brown earth > podzol > gleyed podzol > gley but within some forest blocks, such as Kirkhill, gleys support higher growth than freely drained soils. At higher altitudes climatic limitations override the influence of drainage.