Long-term responses of ecosystem components to stand thinning in young lodgepole pine forest. 1. Population dynamics of northern flying squirrels and red squirrels

A new paradigm in forest management is managing second-growth forests to accelerate development of structural characteristics associated with late-seral forests. A key uncertainty is whether those wildlife species associated with these structural characteristics will respond positively to their development in thinned young seral forests. This study was designed to test the hypothesis that population dynamics (abundance, breeding condition, and survival) of northern flying squirrels (Glaucomys sabrinus) and red squirrels (Tamiasciurus hudsonicus) would be maintained at levels recorded in old-growth forests by large-scale pre-commercial thinning of young (17-27 years old) lodgepole pine (Pinus contorta) forests. Replicated study areas were located near Penticton, Kamloops, and Prince George in south-central British Columbia, Canada. Each study area had three young pine stands thinned to densities of similar to500 (low), similar to1000 (medium), and similar to2000 (high) stems/ha, with unthinned (4300-7600 stems/ha) and old-growth stands for comparison. Populations of G. sabrinus and T. hudsonicus were sampled intensively from 2000 to 2002 corresponding to 12-14 years after thinning. Abundance of G. sabrinus was significantly higher in the high-density stand and lowest in the low-density and unthinned stands. Intermediate densities were found in the medium-density and old-growth stands. Adult male body mass was significantly greater in old-growth than high-density stands. We failed to detect significant differences among treatments for recruitment, movement, and survival for G. sabrinus and all parameters measured for T. hudsonicus. Survival increased significantly in 2002 from previous years for G. sabrinus, while survival decreased significantly for T. hudsonicus during this period. Our results support the hypothesis that population dynamics of G. sabrinus and T. hudsonicus would be maintained at levels recorded in oldgrowth forests by large-scale pre-commercial thinning of young lodgepole pine forests. Abundance of G. sabrinus in highdensity stands exceeded levels recorded in old-growth stands. (C) 2004 Elsevier B.V. All rights reserved.