Development of wood decay in wounded western hemlock and Sitka spruce in southeast Alaska

Sixty-eight western hemlock (Tsuga heterophylla (Rat.) Sarg.) and 51 Sitka spruce (Picea sitchensis (Bong.) Carriere) trees with bole wounds were selected from six locations in southeast Alaska. Each tree was dissected and measured for extent of internal stain and decay to determine wood volume losses over time caused by fungi. The margins of stain and decay associated with bole injuries that ranged from 1 to 80 years old were marked on the surface of 30 cm long bole segments of each tree and then photographed. Areas occupied by stain and decay were measured for each bole segment using AutoCAD digitizing techniques and then the amount of affected volume was computed for each tree. In regression models, original scar width, original scar area, and a transformation of scar age are significantly correlated with the ln(volume of stain + decay) for hemlock; original scar length and a transformation of original scar width are significantly correlated with volume of stain + decay for spruce. Decay extended less than 1 m above wounds and consumed less than 5% of gross tree volume in all but a few trees which had large, old scars. Decay development in hemlock was less extensive than reported in Oregon and Washington; models from these areas greatly overestimate decay in wounded trees in southeast Alaska. Tangential callus growth (one side of the wound) was 2.1 and 1.7 mm/year for spruce and hemlock, respectively. Forest managers may use this information to design stands with acceptable heart rot levels by predicting the development of decay in wounds and by altering schedules of stand thinning and final harvest of wounded trees.