Effect of Habitat-Improvement Thinnings on Lumber Products from Coastal Douglas-Fir.

摘要

We selected 66 sample trees from two thinning treatments, each of which was applied at three sites on the Siuslaw National Forest in Oregon. The first commercial thinnings, conducted in 1992 and 1993, had been designed to accelerate the development of large trees with large branches and other old-growth characteristics so as to improve habitat for bird species that depend on such characteristics. Our sample trees, removed in commercial thinnings from 2008 to 2010, were felled and bucked into long (woods-length) logs whose stems were measured in detail, with surface defects also measured and located in three dimensions. Sample logs from the heavier of the two thinning treatments had larger knots on average than logs from the lighter thinning; they had higher average knot density and percentage of live knots. The long logs were “bucked” by computer simulation into short (mill-length) logs that were then “sawn” by computer simulation into lumber. Logs from the heavier thinning treatment had higher average lumber volume recovery, higher average lumber grade recovery, and higher estimated lumber value than logs from the lighter thinning. The analysis suggested that heavier thinning produced trees with more frequent and larger branches—more suitable for nesting and roosting by the target bird species—while at the same time yielding larger logs from harvested trees that produce higher product values. The product value from trees harvested in such thinnings is likely to be lower than values derived from harvests in nearby industrial forests, but comparable to other thinning treatments that are applied to similar forests on federal lands.