Where the Bison Roam: Public-Private Partnership Supports Potential Restoration

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A little over one hundred years ago, plains bison were prolific in the Great American West. Reports describe herds containing thousands of animals migrating through the central and western states, totaling 20–30 million across their entire range. With commercial, unregulated hunting in the late 1800s came the rapid demise of bison to barely more than 1,000 by 18891. Recently, renewed interest in restoring these massive animals to at least some of their former range has grown. Efforts are being made to establish “conservation herds”—herds that are specifically managed in the public interest by governments and environmental organizations. For the plains bison native to the United States, there are approximately 19,000 animals comprising 54 known conservation herds.

The American Bison Initiative

The presence of wild, free-roaming bison is primarily confined to public lands such as national parks and wildlife refuges. In 2008, the U.S. Department of the Interior released a new initiative to restore American bison in the wild:

This framework for managing bison by the Department of the Interior (DOI) bureaus articulates a basis for improved management of the species and provides a foundation to strengthen existing and build new partnerships with States, Native American tribes, landowners, agricultural interests, conservationists and others interested in bison….

…In appropriate areas, the presence of bison in adequate numbers may help support the restoration or maintenance of other native species and habitats. This in turn would provide inspiration or enjoyment to diverse elements of our society. As demonstrated convincingly at Yellowstone National Park, observing bison ranging freely over the landscape holds a major attraction for the American public. 

Goals of the Initiative include locating suitable areas for establishing new bison conservation herds or expanding existing herds. Also, in A Call to Action, the National Park Service identifies “returning the American bison to our country’s landscape” as one of its most important objectives for the next one hundred years.

Collaboration in Colorado’s San Luis Valley: Bison in the Cold Desert

One area considered for bison restoration is the San Luis Valley in south-central Colorado, where bison roamed until they were extirpated in the late 1800s. This landscape is home to a vast interconnected tract of federal, state, and nongovernmental organization lands, including the Baca National Wildlife Refuge, Great Sand Dunes National Park and Preserve, and The Nature Conservancy’s Medano-Zapata Ranch.  

In the shadow of the iconic Great Sand Dunes, an ongoing public-private partnership is helping to provide information to decisionmakers on questions relating to the potential establishment of a bison conservation herd. USGS scientists from the Fort Collins Science Center (FORT) and the Northern Rocky Mountain Science Center (NOROCK) are working in partnership with Zapata Partners, private ranchers who are contracted to manage the bison for The Nature Conservancy. Additional partners include the National Park Service, U.S. Fish and Wildlife Service, and The Nature Conservancy. Resource managers need scientifically sound information to help them understand how bison interact with both vegetation and the resident elk that inhabit the valley’s ecosystem. Because most of the bison’s native range is classified as arid or semi-arid, it is crucial to understand how vegetation will respond to grazing by two of North America’s largest terrestrial mammals, and how these mammals may affect one another.

Scientific work began in 2005 investigating the ecology, forage relations, and habitat relations of elk and bison in the valley. From 2005–2009, FORT ungulate ecologist Dr. Kate Schoenecker led research on elk and bison movement ecology and habitat interactions. These studies, among the first on ungulates in the Great Sand Dunes ecosystem, significantly add to an understanding of ungulate ecology in a cold-desert ecosystem. To quantify the effects of herbivory (grazing and browsing) on vegetation, investigators compared areas used by both elk and bison to areas used only by elk. Results showed that areas used by both species did not have significantly greater herbaceous offtake (removal) overall than areas used only by elk, suggesting that elk and bison do not occur simultaneously at any one foraging area. Radio-collar data confirmed that elk and bison are selecting and using the same habitat, but are never there at the same time.

Measurements of woody vegetation indicated that levels of browsing on willows were similar in areas used by both elk and bison compared to areas used by only elk, but foraging on cottonwood saplings was greater in communities with both elk and bison, suggesting that bison are browsing cottonwoods but not willows. Perhaps more importantly, in places where fences were placed to eliminate all browsing, researchers found that cottonwood recruitment did not increase, even after 5 years of protection from browsing. These results indicate that water and climate exert more influence on the persistence and new growth of these woody plants than herbivory, and managers would need to consider water-flow regimes if their goal is to increase recruitment of willows and cottonwoods.

The public-private partnership supports both bison ranch management and ecological research.  With no native large predators remaining in the San Luis Valley, bison are gathered and culled each year to maintain herd size. During the bison gathers in 2011 and 2012, researchers worked with ranchers to implant 2200 bison with microchips to facilitate identifying individuals. Also, bison are weighed each year when they are brought in for the annual gather. Using body weight as a proxy for body condition, researchers are correlating information about body condition with precipitation and climate variables. Some climate models suggest this region of Colorado is expected to show earlier impacts from global climate change than other parts of the state. Thus, understanding ecological function and species interactions in arid ecosystems is important for land managers tasked with adapting management to address the effects of climate change.

What’s Next?

In 2008, Dr. Schoenecker and then-USGS scientist Dr. Scott Nielsen (now with the University of Alberta) developed a bison habitat model based on vegetation maps and 3 years of data on radio-collar locations of bison to identify bison habitat and make predictions about which areas bison might use outside of their current range. This model is being updated with new vegetation GIS layers and will be available to decisionmakers in early 2013.

In addition, USGS ecologist Linda Ziegenfuss and Dr. Schoenecker are developing a vegetation monitoring plan to assist resource managers with the National Park Service, the U.S. Fish and Wildlife Service, and The Nature Conservancy. The plan will help managers monitor herbivory in key vegetation communities across this multi-jurisdictional landscape, maintain healthy habitat for ungulates, and conserve sensitive plant communities.

Results and products generated by these projects are already providing resource managers with tools and information for making science-based decisions on bison restoration in the San Luis Valley, and ungulate management in general. Over time, the vegetation monitoring plan and further data on bison body condition in relation to climatic factors will help decisionmakers adapt management of these animals to support their long-term persistence in the area as well as the ecological health of this unique, cold-desert ecosystem.

1Defenders of Wildlife, Basic Facts About Bison
2The ICUN Red List of Endangered Species™, Bison bison

Great Sand Dunes National Park and Preserve: Mammals

IUCN Redlist: Bison bison