Short-term response of breeding birds to oak regeneration treatments in upland hardwood forest.
Abstract
Population declines of several successional-scrub bird species are partly associated with deceased habitat availability as abandoned farmlands return to forest and recently harvested forests regrow. Restoration of mixed-oak (Quercus spp.) forest is also a concern because of widespread oak regeneration failure, especially on moist, productive sites where competition from faster-growing tree species is fierce following stand-replacing disturbances. Several silvicultural methods are proposed to promote oak regeneration but many are not experimentally tested, especially on productive sites. We surveyed birds in 19 stands to assess response to initial application of three proposed oak regeneration treatments on productive sites: prescribed burning (B); oak shelterwood by midstory herbicide (OSW); shelterwood harvests (SW); and controls (C), for one breeding season before and two breeding seasons after, implementation. Relative density of successional-scrub species Indigo Buntings (Passerina cyanea), increased, while Ovenbirds (Seurus aurocapilla) decreased wisthin 11 to 18 months after SW harvests; understory disturbance treatments B or OSW had no effect. Our results indicated that partial harvests created habitat for breeding birds associated with both young and mature forests, whereas understory treatments had little effect. Additionally, we show that even small patches of young forest habitat are used by more individuals and more species of breeding birds than surrounding closed-canopy forest, and may benefit successional-scrub species by enabling their occurrence in an otherwise forested landscape. Absence of several lower-elevation successional-scrub bird species in our mid-elevation SW harvests, suggests that comprehensive conservation in the southern Appalachians necessitates creating and maintaining young forest habitats across elevation gradients.