Twenty-one-year development of Douglas-fir stands repeatedly thinned at varying intervals.

Abstract

Douglas-fir stands first thinned at about age 38 have been observed for 21 years. Four treatments were compared; no thinning, light thinning at 3-year intervals, moderate thinning at 6-year intervals, and heavy thinning at 9-year intervals. Eighteen years after initial thinnings (the first common end to all thinning cycles), all thinned stands had virtually the same total cubic volume as before thinning and about 65 percent of what they would have had without thinning. Early thinnings tended to be from above, later thinnings from below. Thinning interval had no effect on total growth per acre over the 21-year period, but gross growth in all thinned stands was about 20 percent less than that in comparable unthinned stands. There was only about half as much mortality in thinned as in unthinned stands, and enough was salvaged to largely offset the growth loss. Thinning had little effect on current relative tree-size distribution, because increased growth rate of residual trees was offset by removal of many larger-than-average trees. The primary benefit derived from these commercial thinnings was an earlier harvest of products, not a substantial increase in total usable production per acre.

Citation

Reukema, Donald L. 1972. Twenty-one-year development of Douglas-fir stands repeatedly thinned at varying intervals. Res. Pap. PNW-RP-141. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 28 p