WLFW science shows that umbrella species management benefits non-target species that have similar habitat use as target species.
Sage grouse share sagebrush country with hundreds of other species. Some, like the sage grouse, depend on healthy sagebrush habitat for nearly all aspects of their life cycle.
If their habitat is degraded, fragmented, or reduced, they experience population declines. If their habitat is healthy and maintained at scale, their populations thrive.
Because of this, sage grouse are often considered barometers of the overall health of the ecosystem. If sage grouse are doing well, then their sagebrush habitat is healthy, and other species should also be doing well. Conservationists call this the “umbrella species concept.” Wildlife that use the same habitat fall under the “umbrella” of the target species, and umbrella species management is intended to benefit both.
Umbrella species conservation has been seen as an effective way for conservationists to prioritize limited funding and capacity. For example, restoring habitat for sage grouse, an imperiled species that has garnered significant conservation funding, will extend benefits to other species that also live in sagebrush habitat.
However, understanding how populations of non-target species respond to umbrella-species management is important to improving conservation outcomes.
A recent study examined how removing conifer trees for sage grouse impacted abundance and reproductive success of eight songbird species that primarily nest in sagebrush habitat – two sagebrush-dependent species, two shrubland-generalists, and four others that live in sagebrush country but are more associated with edge and woodland habitat.
Researcher Elise Zarri spent four seasons in the Medicine Lodge Valley of southwestern Montana locating nests and tracking nest success in areas where encroaching Douglas fir and juniper trees had been removed and in areas where encroaching trees remained. Her research was generously supported by the Bureau of Land Management, which manages the land where her research took place. Additional funding came from the U.S. Fish and Wildlife Service and additional support came from The Nature Conservancy.
Importantly, Zarri’s research focused both on bird abundance and on how successfully they reproduced over the course of a season. The findings show that population benefits accrue when songbird habitat use aligns with that of sage grouse.
Zarri found that Brewer’s Sparrow, a sagebrush-dependent species, benefited the most with 39% higher density and 63% greater nest success, resulting in 119% higher fledgling production in tree removal areas.
Sage Thrasher, an imperiled sage-obligate in six western states, were never recorded in tree-encroached sites. In tree-free rangelands, daily nest success for this species of conservation concern was 98%.
Vesper Sparrow, a shrubland generalist that shows a preference for more open sites, showed similar results as the sagebrush-dependent species. Vesper’s Sparrow abundance was 308% higher in removed areas and the species produced 660% more fledglings in removed areas than in encroached areas.
Predictably, edge and woodland-associated species, including Green-tailed Towhee, Chipping Sparrow, White-crowned Sparrow, and Dark-eyed Junco were 55-97% denser in tree-encroached rangelands. Nest success was unaffected by tree removal, but fledgling production was 36-96% lower in cut sites due to lower species density. All of these species, excluding towhees, are widespread across North America and are not imperiled in western states.
Green-tailed Towhee population trajectories vary across their western range and are only considered a species of conservation concern in Montana. Towhees typically occupy sagebrush with scattered trees. Lower abundance and fledgling production in Zarri’s results highlight the importance of transitional habitat between forest and sagebrush. Zarri suggests that complete conifer removal may decrease the Towhees’ reproductive output, but future thinning of historic conifer stands adjacent to sagebrush may benefit them.
Ultimately, Zarri’s new science demonstrates the benefits of conifer removal for sagebrush-obligate species. A demographic understanding of all affected species makes for more informed conservation.
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.
Citation: Zarri, E. C., Naugle, D. E., & Martin, T. E. (2024). Impacts of umbrella species management on non-target species. Journal of Applied Ecology, 00, 1–15.
Permanent URL: http://doi.org/10.1111/1365-2664.14654
Acknowledgements: We thank two anonymous reviewers, Mark Hebblewhite, Angela Luis, John Maron and the Martin Lab for their helpful comments on earlier drafts of this manuscript. We thank the many field assistants who made this work possible and the Hansen family for providing access to the field site. We acknowledge that this work was conducted on the traditional lands of the Shoshone-Bannock and other native peoples. We thank them for their stewardship of the land. Funding was provided by the Bureau of Land Management and the US Fish and Wildlife Service.