Butt and Root Decay in Precommercially Thinned SpruceߝFir Stands

Abstract

Abstract To test the effect of precommercial thinning (PCT) on butt decay development, 10 commercial thinning size spruceߝfir stands that were precommercially thinned 10ߝ24 years ago and seven unthinned (UT) control stands were assessed for butt decay incidence. The data indicate that PCT did not increase butt decay incidence for either red spruce or balsam fir compared with UT control stands. However, butt decay incidence increased with dbh, height, age, and years of PCT for balsam fir. These relationships were not found for red spruce. No significant PCT treatment effect was found for either species in root decay incidence (RDI) by examining all roots 1.0 cm or greater in diameter of 80 crop trees. RDI of balsam fir increased as root size increased. A significant relationship (r2 = 0.835) exists between RDI and butt decay proportion in the horizontal stump section for balsam fir. To evaluate whether the PCT operation resulted in the removal of butt-decayed stems preferentially, 55 10 × 10 m plots of precommercially thinned spruceߝfir stands were surveyed within 2 years after thinning. A total of 1,426 red spruce stumps; 2,471 balsam fir stumps; 441 retained red spruce trees; and 419 retained balsam fir trees were examined. The results showed that the practice of PCT tended to result in selecting a higher proportion of decayed trees as crop trees. Overall, 5.7% of retained trees and 1.6% of stumps were determined to have decay for red spruce, and 15.8% of retained trees and 5.6% of the stumps had decay for balsam fir.