Impacts of umbrella species management on non-target species

Abstract

1. 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. 2. 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. 3. 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. 4. 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. 5. 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.