Strip thinning and selective thinning in Douglas-fir [Pseudotsuga menziesii]

Tree growth was compared on plots that had been strip thinned, selectively thinned, and not thinned in a 35-year-old Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] stand. The ratio of basal area increment five years after thinning to basal area increment five years before thinning was larger for all thinning treatments than for the control. However, trees farther than 10 feet from the edges of thinned strips did not respond. Individual tree growth and net stand basal area increment were greater in selectively thinned plots than strip-thinned ones after similar percentages of initial basal area were removed in each. Net stand basal area increment after five years was greater in selectively thinned plots than in strip-thinned ones even where 20 percent more trees had been removed. Nevertheless, lower logging costs and increased silvicultural flexibility may make strip thinning a desirable alternative in some cases.