Development of epicormic sprouts in Sitka spruce following thinning and pruning in south-east Alaska

The frequency and size of epicormic sprouts in Sitka spruce (Picea sitchensis (Bong.) Carr.) were assessed in five 23-29-year-old mixed Sitka spruce-western hemlock (Tsuga heterophylla (Raf.) Sarg.) stands that were uniformly thinned and pruned to 2.4, 3.7 and 5.2 m lift heights. Six to nine years after treatment sprouts were very common with 232 of 236 trees producing sprouts and an average of 9-11 sprouts m(-1) of tree bole. The total numbers of sprouts were similar for the different pruning treatments but significantly more large sprouts (P = 0.025) were produced in the 5.2 m pruning lift. Trees that developed large sprouts were significantly smaller, shorter and had less crown length at the time of pruning than trees without large sprouts. Our results suggest that spruce responds to thinning and pruning treatments with the production of numerous epicormic sprouts. If one of the main goals of pruning is to produce clear, higher-valued wood, Sitka spruce may be a poor candidate species for pruning.