Sage Grouse Populations Grow Faster After Tree Removal

In Oregon, a long-term study of sage grouse and conifer removal showed that grouse population growth rates increased 12% following conifer removal. This before and after photograph demonstrates just how much conifer encroachment existed on the site prior to removal. Credit: Todd Forbes, BLM, Lakeview District.

Restoring wide-open sagebrush habitat in southern Oregon benefits birds and ranchers

By Brianna Randall, Sage Grouse Initiative, Working Lands for Wildlife

In Oregon’s Warner Mountains, sagebrush rolls across hillsides and valley bottoms, providing productive land for livestock and wildlife. Like many places in the West, these valuable rangelands are at risk from encroaching trees that displace wildlife, reduce livestock forage, and decrease available water. More than one million acres of sagebrush grazing lands in the Great Basin have turned into pinyon-juniper forests in the past two decades alone.

This photograph shows the “control area” in the Warner Mountains. This area did not have any tree removal and it demonstrates how conifer encroachment impacts sagebrush habitat. Photo: Andrew Olsen.

Fortunately, new research from an eight-year study in the Warner Mountains shows that strategically removing encroaching trees spells good news for sage grouse, a declining upland bird that serves as a benchmark species for the overall health of the sagebrush biome. This adds to a growing list of research — much of it based on the long-term study in the Warners — that documents the myriad benefits of conifer removal for wildlife and grazing lands.

This graph shows how sage grouse population growth rates increased as conifer trees were removed from the landscape. Credit: Andrew Olsen.

“In places where junipers were removed, the sage grouse population grew at a rate that was 12 percent greater than in an area where no trees were cut,” explained Andrew Olsen, who led the research for Oregon State University. “By targeting removal where sagebrush plants were still intact, we bought instant habitat for a declining bird species.”

Sage grouse suffer when trees take over. Birds avoid mating or nesting if there are more than a few trees on the landscape, likely because conifer woodlands are riskier habitats for grouse with more predators. Other sagebrush-reliant wildlife like mule deer and songbirds are also negatively impacted when conifers crowd out the perennial plants they need for food and cover.

Map of study area in the Warner Mountains of Oregon, California, and Nevada. Credit: Andrew Olsen.

Unfortunately, trees are taking over America’s grazing lands at an alarming rate. Conifers like Western Juniper have expanded by as much as 600% over the last 150 years — and 90 percent of that expansion has occurred in sagebrush country.

Olsen’s research demonstrates how removing expanding conifers before they get too dense can bring back the birds. A previous study from the Warner Mountains found that 29% of marked hens moved back to nest in restored habitat just three years after conifers were cut. Additional research in the Warners also revealed the abundance of sagebrush-loving songbirds doubled following juniper removal.

“While conifer removal in the Warners has been shown to help sage grouse, many different wildlife and plant species are also benefiting from the restoration of these open sagebrush habitats,” said Todd Forbes, district manager of the Bureau of Land Management’s Lakeview District in Oregon.