Avian occupancy response to oak woodland and savanna restoration

Abstract

ABSTRACTOak (Quercus spp.) woodlands and savannas throughout the Mid‐South, USA have become closed‐canopy forests through succession in the absence of fire, contributing to declines in disturbance‐dependent avian species. Restoration could ameliorate these trends, but effects of such management practices on avian communities of the Mid‐South are poorly understood. We implemented an experiment on the Cumberland Plateau, Tennessee with treatments involving fall (Oct) or spring (Mar) fire with woodland (14 m2/ha) or savanna (7 m2/ha) residual basal area and unmanaged control stands (20 ha each). We conducted fixed‐radius point counts 3 times annually (2010–2012) and analyzed trends in naïve occupancy for 41 species. For 20 species with adequate data (10 early‐, 10 late‐successional), we performed multiple‐season, robust‐design occupancy modeling and accounted for detection bias. We then used mixed‐model polynomial regression to define relationships between occupancy and measures of live and dead basal area, midstory density, and herbaceous groundcover. Restoration substantially altered forest structural characteristics but did not affect the occupancy of most late‐successional species. In contrast, the presence of early‐successional species increased as live basal area decreased and herbaceous groundcover increased. Only 3 of 41 species (hooded warbler [Setophaga citrina], ovenbird [Seiurus aurocapilla], and worm‐eating warbler [Helmitheros vermivorum]) exhibited reduced occupancy as woodland and savanna conditions were approached. The presence of all other species, including 13 regionally and 2 continentally declining, remained constant or increased as restoration progressed. Woodland conditions of 10 m2/ha live basal area and 20% herbaceous groundcover maximized occupancy of early‐successional species with little consequences for late‐successional species. Proceeding further toward savanna conditions negatively affected species associated with lower strata of mature‐forests but further increased the presence of some early‐successional species. Midstory density and dead basal area were poor predictors of occupancy and thus may be necessary but not sufficient in promoting early‐successional species. Our results suggest implementing oak woodland and savanna management in the Mid‐South could benefit disturbance‐dependent birds of high conservation priority with minimal negative impacts on the presence of late‐successional species. © 2016 The Wildlife Society.