| Permanent study plots were established in Southeast Alaska in 1990, 1991, and 1992 to monitor and quantify the growth responses of western hemlock (Tsuga heterophylla (Raf.) Sarg.) and Sitka spruce (Picea sitchensis (Bong.) Carr.) to thinning and pruning. Young trees in mixed stands were thinned to 170 trees per acre (420 trees/ha) and pruned to three different heights--8, 12, and 17.4 feet (2.4, 3.7, and 5.3 m). Branch sizes and time-and-motion data were recorded and analyzed to determine the functional relationships between time required to prune and branch characteristics. Pruned height and stem diameter were significant variables for predicting time required to prune. Epicormic branching, sunscald, and tree mortality were monitored to determine how pruning to various heights affects stem quality and tree survival. Epicormic sprouts increased on spruces but differences in numbers of epicormics between treatments were statistically nonsignificant in the first two years after treatment. Stem diameter, basal area, and butt log volume growth differences between treatments were statistically significant in the first year; and diameter growth differences were significant in the second year after treatment. Height growth differences between treatments were statistically nonsignificant in the first two years after treatment. Percent live crown length removed in combination with initial stem diameter and live crown ratio in combination with initial stem diameter were significant variables in multiple regression models for predicting posttreatment stem diameter, basal area, and volume growth. Growth was significantly reduced when 40 percent or more live crown length was removed and when live crown ratios were reduced below 50 percent. Mean stem diameter growth in the 17.4-foot (5.3 m) lift was significantly reduced at 4.5 feet (1.4 m) above the ground but not at 17.4 feet (5.3 m) resulting in significant changes in stem taper after treatment. |
