Forest canopy reduction and breeding bird responses: treatment- and temporal-dependent patterns.
Abstract
We examined the effects of oak regeneration forest management treatments on territorial density of breeding forest birds. The study area was located on the southern end of the mid-Cumberland Plateau in northern Jackson County, AL. Fifteen 4-ha stands were treated in 2001 with one of five target overstory retention (percentage) treatments: 0 (clearcut); 25; 50; 75; and 100 (control). In 2010-2011, the residual trees in the initial 25, 50, 75, and 100 (control) percent retention stands were harvested, and three new controls were added, which resulted in three forest stand cohorts: (1) mature (control, not harvested for 50 to 70 years); (2) 10-year-old regenerated clearcut; and (3) final harvest of the shelterwood prescriptions (25, 50, 75, and 100 percent retention stands in 2001). Breeding songbirds were surveyed 9 to 10 times per year during the peak of breeding season (April to July) of 2002, 2003, 2010, 2011, and 2012. Territory mapping was used based on detections in each year in each stand. Two-way analysis of variance (ANOVA) and Tukey test were used to compare average territory density among treatments and years. Results of temporal responses of two breeding songbird conservation concern species, Kentucky Warbler (Geothlypis formosa) and Worm-eating Warbler (Helmitheros vermivorum), to treatments showed that responses were treatment-dependent. Territory density of Kentucky Warbler (an interior-edge species) showed positive response to 50 percent retention stands. Worm-eating Warbler (an interior species) territory density responded positively to control stands.