Long-term basal area and diameter growth responses of western hemlock-sitka spruce stands in southeast Alaska to a range of thinning intensities.

To better understand the long-term basal area and diameter growth response of young, well-stocked, even-aged, mixed-species stands of western hemlock (Tsuga heterophylla (Raf.) Sarg.) and Sitka spruce (Picea sitchensis (Bong.) Carr.) to a range of thinning intensities (heavy, moderate, light, and unthinned), 20 years of posttreatment (i.e., thinning) data were analyzed from 128 permanent study plots at 32 installations in southeast Alaska. Thinning significantly increased the basal area growth of the thinned plots relative to that of the unthinned plots. Basal area growth of the thinned plots decreased with increasing thinning intensity, likely a consequence of the reduction in growing stock with increasing thinning intensity. Diameter growth increased with increasing thinning intensity. Younger stands (typically with smaller pretreatment basal areas and diameters) responded more vigorously to thinning than did older stands, as did stands growing on more productive sites. The models developed in this analysis can be used by land managers to make general predictions of how western hemlock-Sitka spruce stands similar to those investigated in southeast Alaska are likely to respond to different thinning intensities in terms basal area and diameter growth during the first 20 years posttreatment.