The effect of whole-tree harvesting on the growth of second rotation Sitka spruce

Abstract

Summary Stem analysis has been used to examine the effects of two harvesting techniques upon growth of second rotation Sitka spruce planted in 1981 on a peaty gley site of low fertility in Kielder Forest, Northumberland. The effect of NPK fertilizer upon tree growth on conventionall y harvested plots was also determined. Weed competition was reduced by hand weeding and the application of herbicides. Repeated measures analysis was used to identify the time at which significant growth responses occurred. Whole-tree harvesting reduced mean tree volume from 1986 onwards while the addition of fertilizer to conventionall y harvested plots increased volume growth from 1990. By 1993, whole-tree harvesting had decreased mean tree volume by 32 per cent and the addition of fertilizer to conventionally harvested plots had increased mean tree volume by 13 per cent. Observed treatment effects are most likely due to the increased removal of nutrients during whole-tree harvesting. The release of nutrients from decomposing residues is expected to meet uptake requirements for approximately 7-9 years following replanting. Effects of shelter and weed competition should also be considered on sites where herbicides have not been used to control ground vegetation. Repeated measures analysis and the use of suitable growth functions provide powerful analytical tools to examine historical treatment effects derived from stem analysis.