Subcanopy response to variable-density thinning in second growth forests of the Pacific Northwest

Variable-density thinning (VDT) is a management option designed to increase structural heterogeneity in second-growth conifer stands. This study examined subcanopy tree growth response to two variations of VDT.;At the Forest Ecosystem Study in western Washington, thinning intensity was found to have a significant effect on height growth of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings which established following the thinning. At the Olympic Habitat Development Study in western Washington, basal area growth response was examined for residual midcanopy western hemlock (Tsuga heterophylla (Raf.) Sarg.) and western redcedar (Thuja plicata ex. D. Don). Both species retained the ability to respond to thinning.;The results of this study suggest that non-uniform thinning practices, like VDT, can lead to variation in growth response of residual subcanopy trees and new regeneration. This may accelerate the development of more structurally diverse forests than traditional management practices.;Key words: variable-density thinning, forest structure, subcanopy...