Effects of retention harvests on structure of old-growth Pinus strobus L. stands in Ontario

Retention of structural elements, or legacies, of old-growth stands at harvest has been proposed as a means of maintaining wildlife habitat and ecosystem function in managed forests. However, little is known of the effects and consequences of such practices on the residual stand. A “structural retention harvest” of old-growth eastern white pine Pinus strobus L. was carried out in 1992 in the Algoma Forest of Central Ontario, Canada. In contrast to then-current guidelines, declining- and cavity-trees, snags and coarse woody debris (cwd) were retained at harvest. Cut and uncut stands were surveyed in 2001 to determine the effects of this harvest on forest structure. Basal area prism sweeps for trees and snags were taken at 100 m spacing in 12 logged and six unlogged stands in August 2001. Ground cover, regeneration, and cwd were recorded. White pine basal area before harvest varied among stands from 4.5 to 25.7 m2 ha−1, or 21-68% of stand total. No white pine trees below 18 cm dbh were found. Around half of white pine basal area was removed at harvest. Logging damage was found on 7% of residual white pines. Harvested stands had similar numbers of cavity trees, standing snags, and volume of natural-origin cwd, to unharvested stands. Inputs of logged white pines left in situ increased the total volume of cwd in harvested stands compared with unharvested stands. Harvested stands also contained more recently dead pines and tip-over trees than unharvested stands. White pine regeneration was scarce, though marginally greater in cut stands. Regeneration was correlated with increased canopy openness in cut stands. Herbaceous cover and sapling density was greater in harvested stands. The study shows that structural retention harvesting can maintain or exceed levels of habitat provision such as cavity trees and cwd, found in old stands, though increased tree mortality and wind-throw can result.