A Comparison of Distance-Dependent Competition Measures for Height and Basal Area Growth of Individual Conifer Trees

Abstract

Abstract The effect of competition on height and diameter² growth of individual conifer trees was examined. In this paper we modeled growth of individual trees as a product of potential growth reduced by competition. We investigated a number of competition indices that incorporate tree sizes and distances from neighbors, evaluated over varying competition zones. For these indices the reduction in mean square error relative to no competition index was used to judge performance. The performance of these indices varies by species and growth component (height or diameter² growth), but performance was generally better for tolerant white fir than for intolerant ponderosa pine. Additional competition measures that incorporate estimated crown parameters were developed and shown to improve on many of the traditional competition measures especially for ponderosa pine and Douglas-fir. For white fir, basal area performed well, but not as well as the individual tree competition indices that incorporate estimated crown parameters. We found that expanding the search zone did not improve our ability to estimate competitive effects. Choosing competitors with a height angle gauge was generally superior to selecting them with a DBH angle gauge. Results are summarized by species, type of competition index, and competition evaluation zone. For. Sci. 38(3):695-720.