Impacts of umbrella species management on non‐target species

Abstract

Restoration of anthropogenically altered habitats has often focused on management for umbrella species—vulnerable species whose conservation is thought to benefit co‐occurring species. Woody plant encroachment is a form of habitat alteration occurring in grasslands and shrublands around the globe, driven by anthropogenic shifts in disturbance regimes. Conifer encroachment is a pervasive threat to historically widespread sagebrush communities, as trees outcompete sagebrush and can negatively affect sagebrush‐obligate animal species. Degradation and loss of sagebrush plant communities in western North America have been associated with drastic declines in wildlife populations. The imperilled Greater Sage‐Grouse is assumed to be an umbrella species for the sagebrush community, so habitat restoration, including removal of encroaching conifers, is commonly targeted towards sage‐grouse. How this conservation action affects the demography of species other than sage‐grouse is largely unknown. We quantified the demographic effects of landscape‐level restoration of sagebrush communities through conifer removal on an assemblage of sagebrush‐obligate, shrubland generalist and woodland‐associated songbirds. We compared songbird density and reproduction between adjacent restored and uncut conifer‐encroached sagebrush plots in southwest Montana. We found and monitored nests to record nest fate and number of offspring produced. We found demographic benefits for sagebrush‐obligate species in restored areas. Sage Thrashers colonized restored areas. Brewer's Sparrow density was 39% higher and nest success was 63% higher in removal treatments, resulting in 119% higher fledgling production compared with uncut areas. The density of Vesper Sparrows, a shrubland generalist, was 308% higher and fledgling production was 660% higher in restored areas. Another shrubland generalist, the White‐crowned Sparrow, experienced 55% lower density and 37% lower fledgling production in conifer removal areas. Two woodland‐associated species, Chipping Sparrows and Dark‐eyed Juncos, were nearly extirpated following conifer removal. A third woodland associate, the Green‐tailed Towhee, experienced 57% lower density and 69% lower fledgling production in removal than non‐removal areas. Synthesis and applications. Our study demonstrates the benefits of conifer removal for sagebrush‐obligate species, while highlighting species that may be sensitive. Umbrella species management can benefit co‐occurring species with similar habitat associations, but demographic analyses for all impacted species are essential for effective conservation.