Growth of site trees and stand structure in mixed stands of Pacific silver fir and western hemlock.

Abstract

Height and diameter growth of Pacific silver fir (Abies amabilis Dougl. ex Forbes) and western hemlock (Tsuga heterophylla (Raf.) Sarg.) site trees, as well as overall stand structure on 0.15-acre plots, were analyzed in mixed stands 43 to 57 years old in breast height age at six locations in western Washington. These mixed stands have produced volumes of 9,160 to 20,200 cubic feet per acre. Early height and diameter growth of hemlock site trees was greater than that of silver fir. After 30 to 45 years of growth, the predicted site index of silver fir was 1 to 2 feet greater than that of hemlock at four locations and 11 feet greater than that of hemlock at one location. Hemlock site trees were larger in diameter at breast height (d.b.h.) than silver fir 30 years before present, but since that time the rate of d.b.h, growth has decreased for both species, with less decrease for silver fir than for hemlock: Silver fir and hemlock were present in all crown classes, and both species had the same range in d.b.h, at three locations. Silver fir generally had, however, a greater proportion of larger stems than did hemlock. At five locations, silver fir had fewer stems per acre than hemlock, but this true fir contributed more volume per acre in proportion to number of stems than hemlock did. Silver fir was an important component of these mixed stands and should be treated similarly to hemlock during precommercial and commercial thinning.

Citation

Murray, Marshall D.; Leonard, Peggy C. 1990. Growth of site trees and stand structure in mixed stands of Pacific silver fir and western hemlock. Res. Pap. PNW-RP-431. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 12 p