The relationship between upland hardwood distribution and avian occupancy in fire-maintained longleaf pine forests

Abstract

Prescribed fire and other forest management practices aimed at restoring longleaf pine (Pinus palustris) communities often focus on the reduction, or removal, of upland hardwoods with the goal of providing habitat for threatened and endangered plant and animal species, including the federally endangered red-cockaded woodpecker (Leuconotopicus borealis), and restoring forests to pre-settlement conditions. Although contemporary restoration and management practices benefit species dependent on the resulting conditions, recent research has called attention to the ecological value of retaining upland hardwoods, especially for mast-dependent wildlife (e.g., fox squirrels [Sciurus niger]). Moreover, retention of indigenous hardwoods in upland longleaf pine communities may benefit a variety of birds. We used fixed-radius, breeding season point counts to sample the presence-absence of 15 avian species and assessed forest composition and structure around each point. We developed single-season single-species occupancy models with an emphasis on the influence of overstory hardwood cover on occupancy. Due to issues with model fit, we were unable to model occupancy for 3 of the 15 focal species. Occupancy probabilities for 6 out of the 12 focal species were positively influenced by overstory hardwood cover or stem density, whereas occupancy probabilities of 4 out of 12 of the focal species was negatively influenced by hardwood cover or stem density. Overstory hardwood cover between 5 and 15% resulted in high occupancy probabilities for the species that were positively influenced but did not result in substantially low occupancy probabilities for the species that were negatively influenced. Longleaf pine uplands with lower and upper bounds of 5% to 15% hardwood overstory cover with hardwood stem densities of ≤250 stems/ha could be targeted to provide habitat for the greatest diversity of birds while avoiding negative impact to species associated with upland longleaf pine communities.