Effect of whole-tree harvesting on microclimate during establishment of second rotation forestry

The effect of whole-tree harvesting on microclimate during the restocking of three upland forest sites in the UK was studied from January 1994 to November 1999. Mean soil temperatures at 0.1 m depth were greater during summer months and reduced during winter months at all three sites in whole-tree harvested treatments compared to those where harvest residues were retained on site. Whole-tree harvesting also affected mean shoot temperatures (0.3 m above ground level) at each of the three sites and, for much of the time, the effects on shoot temperatures were the reverse of those observed for the soil. In comparison to conventional harvesting, shoots on whole-tree harvested plots tended to be cooler in spring and summer whereas the same shoots were warmer during winter. Whole-tree harvesting increased mean wind speeds measured at 0.3 m by around 40% at each of the three sites during the first year after replanting. This effect diminished to 26, 20 and 5% over the following 3 years at the one site studied for the longest period, located in Kielder Forest, Northumberland. The biomass of 4-year-old Sitka spruce trees was greater on whole-tree harvested plots at two sites where growth was increased by fertiliser applications but was not affected by harvesting treatment at the more fertile third site in which no response to fertiliser was observed.