Crown Development and Site Estimates in a Douglas-Fir Plantation Spacing Test

Abstract

Abstract Relationships among stem and crown dimensions of Douglas-fir were examined 43 years after planting on site IV land at initial spacings of 4×4 through 12×12 feet. Average dbh, height, and crown dimensions of the largest trees (largest 20 percent or 100 trees per acre by dbh) and of comparable crown classes all increased consistently with increase in initial spacing. Trees of similar dbh or total height were currently quite similar in crown dimensions, although they had arrived at this condition by somewhat different routes. Striking differences among spacings in apparent site indices are attributed mainly to restriction of height growth by competition rather than to real site differences. Average heights of several stand components were compared as bases for site index estimates; heights of a fixed number of the largest diameter trees were most nearly consistent among spacings, although no procedure eliminated spacing effects. Comparisons suggest possible usefulness of live-crown length as one criterion for acceptable site trees in stands of abnormal density. High initial density in low-site stands can lead to serious underestimates of potential productivity. Forest Sci. 16:287-301.