Pacific Northwest Research Station

Title: Growth and yield of western hemlock in the Pacific Northwest following thinning near the time of initial crown closure.

Author: Hoyer, Gerald E.; Swanzy, Jon D.

Date: 1986

Source: Res. Pap. PNW-RP-365. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 52 p

Station ID: RP-PNW-365

Description: Growth, stand development, and yield were studied for young, thinned western hemlock (Tsuga heterophylla Raf. [Sarg.]). Two similar studies were located at Cascade Head Experimental Forest in the Siuslaw National Forest, western Oregon, and near Clallam Bay on the Olympic Peninsula in Washington. At the latter, first thinnings were made at two ages; one at about the time of initial crown closure (early or crown closure thinning), and the other after competition was well underway (late or competition thinning).

Stands, age 7 at breast height at time of crown closure thinning, were grown for 17 years at Cascade Head and for 11 years at Clallam Bay. In addition, 6 years after (early) crown-closure thinning the first (late) competition thinning was made at Clallam Bay on previously prepared, well-stocked stands. The tree spacing on the early thinnings ranged from 3 feet to 22 feet.

At ages 24 and 18 breast height on the two studies, stands with the most stocking produced the most cubic-foot volume and volume increment and the smallest average diameter. Early thinnings spaced between 7 and 12 feet produced the most usable wood in terms of Scribner board-foot volume of trees 6 inches in diameter and larger.

During the 6-year period following the late thinning, the treatments produced 55, 86, and 180 more cubic-foot volume increment per acre per year than did early thinnings that grew to the same basal area. The studies provide an approximation of the behavior of stands grown at given plantation spacings. The studies suggest that volume increment from stands thinned late differs from the volume increment of early thinning or planted stands that have attained basal area density similar to the late-thinned stands. Representative growth and yield data is provided for all treatments.

Keywords: Spacing thinnings, stand development, increment, yield (forest), western hemlock

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Citation

Hoyer, Gerald E.; Swanzy, Jon D.  1986.  Growth and yield of western hemlock in the Pacific Northwest following thinning near the time of initial crown closure..   Res. Pap. PNW-RP-365. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 52 p