Initial thinning effects in 70- to 150-year-old Douglas-fir--western Oregon and Washington.

Abstract

Vigorous, mature (post-rotation age) Douglas-fir stands will probably exist for another 50 years or more on some properties in western Oregon and Washington. Intermediate harvests in the form of thinnings were analyzed on nine study areas ranging from 70 to 150 years old when thinned. Recoverable cubic-volume growth, averaging 81 percent of normal gross growth, was recorded for up to 38 years with single thinnings and for 18 years with two thinnings. This percentage increases with stand age, but rate of response to thinning decreases with increasing stand age. A dramatic 61-percent reduction in loss caused by bark beetles and substantial reductions in losses from windthrow (30 percent), breakage (33 percent), and suppression (46 percent) were measured. Reserve basal area may be maintained between 60 and 85 percent of normal. Thinning should follow marking guidelines previously recommended but with more emphasis on crown release since spacing is important in vigorous, mature stands as well as in younger stands.

Citation

Williamson, Richard L.; Price, Frank E. 1971. Initial thinning effects in 70- to 150-year-old Douglas-fir--western Oregon and Washington. Res. Pap. PNW-RP-117. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 21 p