Bison Effects: Research and Monitoring

Three bison below a steep rock ledge
Bison spotted at the bottom of the Kaibab limestone layer below the North Rim of the Grand Canyon during a winter aerial survey.

USGS Photo/ K. Schoenecker

Bison Safety

  • Bison are wild animals and are unpredictable.
  • Maintain a distance of 100 feet (30 m or two bus lengths) from bison.
  • When the bison are within 100 feet (30 m) of the road, it is recommended to view theme from inside a vehicle.
  • Please use established gravel or paved pull-outs to park vehicles completely off the roadway (all wheels right of the white line). Do not walk or park in the road.

Why monitor bison effects?

In Grand Canyon National Park, bison are only found on the North Rim on the Kaibab Plateau. The Kaibab Plateau bison herd lives in a high elevation desert environment. They graze and wallow in park meadows, stampede through dense forests, winter along the rim of the canyon, and venture below the Kaibab limestone layer within the Grand Canyon. Historically bison in this area, at the edge or just outside of their range, would have occurred in small intermittent numbers at low density. Now however they are limited by human geography and tolerance. We know quite a bit about how bison interact in ecosystems such as the tall and short grass prairie where they are often in denser numbers but little about them in habitat similar to the Kaibab Plateau. There are concerns about the density of bison and effects they might have on this different ecosystem.

Effects of bison occur on both large and small spatial scales including: increased vegetation heterogeneity, nutrient redistribution, changes in plant species composition, creation and maintenance of grasslands, increased productivity in grasslands, competition with other herbivores, modification of fire regimes, modification of hydrological processes, and disturbance of woody vegetation. All of these effects can change wildlife habitat in ways that support some species and limit others, producing cascading effects on biodiversity and species composition. It is important to note that bison are a native grazer and the effects are likely different from that of cattle. Park staff and collaborators have undertaken research to learn more about local effects and to monitor them over time so that the herd can be managed at a size that is sustainable.

What do the studies show?

Effects of Herbivory
There is an observable difference in vegetation height, cover, and litter accumulation between areas grazed by bison and those not. However, research at water sources indicate that there is no difference in plant species richness between grazed and ungrazed areas nor is there a difference in soil compaction (Reimondo 2012, Terwilliger et al. 2000) although there is greater forb cover in grazed areas than graminoids (Terwilliger et al. 2000).

For more details see: Currently the park is working with the U.S. Geological Survey and Colorado State University to study the effects of bison herbivory using large exclosures.

Effected Water Quality:
The drinking water in Grand Canyon National Park comes from Roaring Springs, fed by rain and snowmelt on the North Rim. Monitoring has indicated increased levels of E. coli bacteria in standing water associated with bison grazing areas. Large ungulate herds are known to cause significant damage to water sources through contamination and soil compaction.

A herd of thirty bison stand in water source. The edge of the water is muddied and compact while the surrounding grass is trampled and littered with bison feces.
Soil compaction and water contamination by bison herd on the North Rim of Grand Canyon National Park, 2017. (NPS camera trap photo)

Threats to Archeological Sites:
Park archeologists have found significant threats to culturally rich areas of the North Rim from the ongoing impacts of the Kaibab Plateau bison herd. Research shows that these bison follow migratory patterns in search of water and resources. In doing so, the herds trample through archeological sites causing damage to artifacts and cultural features found on the surface and buried underground. This is apparent in the wallows and bison trails surrounding and within survey sites.

Large wallows and deep game trail in grassy meadow near forest's edge.
Large wallows and deep game trail in meadows on the North Rim, 2012.

Grand Canyon National Park

Last updated: March 8, 2023