Effects of respacing on young Sitka spruce crops

Stands of 9- to 11-year-old Sitka spruce with 2000 trees ha(-1) growing at elevations between 150 and 500 m in southern Scotland were respaced to leave 1500, 1000, and 500 trees ha(-1). Fifteen years later, there was no loss of volume production relative to control plots (2000 trees ha-l) when only 1500 trees remained and even with only 1000 trees ha(-1), amounts of standing volume differed significantly from control plots only at the highest altitude site. Height growth was unaffected by respacing but as expected, stem taper was significantly greater at wide spacings (P less than or equal to 0.001) and most pronounced at the most exposed high altitude site. Although there were no significant differences of timber density at breast height for trees growing at differing spacings, timber density decreased significantly with increasing stem girth. However, r(2) accounted for only 15 per cent of the variation. Branch size and the frequency of large branches (>25 mm thick) increased significantly as intertree spacing increased. Although removal of up to 50 per cent of stems had little effect on timber volume production, early respacing dramatically increased coarse branching which could restrict the end uses of the timber.