The distribution and productivity of Sitka spruce (Picea sitchensis) in Ireland in relation to site, soil and climatic factors.

An analysis of the geographic distribution and productivity of Sitka spruce with reference to site, soil and climate characteristics, planted between the years 1924–1991 was conducted. Sitka spruce plantations have been established throughout Ireland from latitude 51oN on Cape Clear Island off the south-west coast of Co. Cork, to 55oN on the Inishowen Peninsula in Co. Donegal. Climate models were used to characterise the range in rainfall and temperature of sites afforested with Sitka spruce. Annual accumulated temperature above 5oC and growing season potential water balance (deficit or surplus) were used to derive five climate zones. Seventy percent of Sitka spruce stands had annual accumulated temperatures >1200 degree days per year. Only 7% of the area was classified as having a potential growing season water deficit. Sitka spruce has been most commonly planted on Mountain and Hill sites below the 450 m contour, typically on peat, gley and podzol soils. A stratified random sampling scheme was used to assess productivity on different soils, climate zones and elevation classes. Results indicate that the most productive stands occurred on deep, moist, well-aerated soils, of moderate to rich nutrient status. Yields on low and high level blanket peats were significantly lower than on greybrown podzolics, acid brown earths, brown earths and gley soils. Productivity varied between elevation classes, but was only significantly lower at elevations over 500 m. Significantly lower yields were found in high rainfall areas where rainfall exceeded potential evapotranspiration by more than 150 mm during the growing season. These areas are associated with blanket peat, peaty podzol and lithosol soils. The national average weighted yield class was found to be 17.0 m3ha-1a-1.