THE EFFECT OF WHOLE-TREE HARVESTING ON THE GROWTH OF 2ND ROTATION SITKA SPRUCE

Stem analysis has been used to examine the effects of two harvesting t echniques upon growth of second rotation Sitka spruce planted in 1981 on a peaty gley site of low fertility in Kielder Forest, Northumberlan d. The effect of NPK fertilizer upon tree growth on conventionally har vested 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 o ccurred. Whole-tree harvesting reduced mean tree volume from 1986 onwa rds while the addition of fertilizer to conventionally 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 fertili zer to conventionally harvested plots had increased mean tree volume b y 13 per cent. Observed treatment effects are most likely due to the i ncreased removal of nutrients during whole-tree harvesting. The releas e of nutrients from decomposing residues is expected to meet uptake re quirements for approximately 7-9 years following replanting. Effects o f shelter and weed competition should also be considered on sites wher e herbicides have not been used to control ground vegetation. Repeated measures analysis and the use of suitable growth functions provide po werful analytical tools to examine historical treatment effects derive d from stem analysis.