Spatial patterns of overstory trees in late-successional conifer forests

Abstract

We analyzed spatial patterns of overstory trees in late-successional Abies amabilis (Dougl. ex Loud.) Dougl. ex J. Forbes forests and late-successional Pseudotsuga menziesii (Mirb.) Franco forests to establish reference spatial patterns for restoration thinning treatments, and to determine whether thinning treatments with minimum intertree spacing rules result in spatial patterns characteristic of late-successional forests. On average, 32.7% of overstory trees in Abies plots and 26.3% of overstory trees in Pseudotsuga plots occurred as members of multitree clusters (groups of trees in which trees are spaced within a specified minimum distance of each other) at a distance of 3.0 and 4.0 m, respectively. Multitree clusters occurred throughout the three Abies plots; the distribution of multitree clusters within the two Pseudotsuga plots was variable. Spatial patterns of overstory trees in late-successional forests were significantly different from those created by simulated restoration thinning treatments. Restoration thinning treatments that release both individual trees and multitree clusters promote characteristic late-successional tree spatial patterns at the within-patch scale (<0.04 ha). This formulation of restoration thinning highlights conservation of existing small-scale (<0.04 ha) spatial heterogeneity within the treatment area, elaborating on current practices that emphasize introduction of spatial heterogeneity at scales of 0.04 ha to 1.0 ha.