Bison Habitat Suitability Project
A study of the Pink Mountain, British Columbia region
The Issue
The plains bison (Bison bison bison), once ranging from northern Canada to southern Mexico, is threatened in Canada, as they currently occupy less than 0.5% of their former range. In Canada, wild plains bison were completely extirpated in the late 19th century and are designated as “threatened” by the Committee On the Status of Endangered Wildlife in Canada. The biggest threat to their recovery is a lack of habitat in which they are considered compatible.
Plains bison are habitat generalists and can persist in many different grassland and forest types. This picture shows a bison and some of the habitat present in the Pink Mountain region.
Location
The Pink Mountain plains bison herd was introduced into the Halfway and Sikanni Chief drainage basins north of Fort St. John, British Columbia, in 1971. Currently, about 1,000 individuals exist within the herd, it the largest free ranging herd in the world.
The diverse land base of the Pink Mountain region with many resource pressures and values makes the herd of great interest to a variety of stakeholders. Knowing whether the habitat is suitable for bison would be a first step in developing a long-range plan for species management.
There has never been a formal study of the suitability of the Pink Mountain area to sustain a herd of such a large ungulate. We set out to determine if the Pink Mountain region contains plains bison suitable habitat by developing a Habitat Suitability Index, or HSI. An HSI calculation represents the capacity of a given habitat to support a selected fish or wildlife species and ranges from a value of 0 (terrible habitat) to 10 (optimal habitat).
Further, we will define the spatial distribution of suitable habitat in winter and summer for plains bison in the Pink Mountain region.
This map shows the study area. The town of Pink Mountain is approximately 180 km north-west of Fort St. John and 200 km south of Fort Nelson, British Columbia. The primary study area lies directly west of this town on the Alaska Highway, along the foothills of the Rocky Mountains.
How did we approach this question?
To obtain an overall habitat suitability index, a number of variables must be considered, some related to availability of food and water, and some related to the habitat itself. Each variable is of different importance to the bison: for example, landcover is twice as important as slope and distance to water in the summer.
Data was gathered from a number of sources in order to calculate the parameters shown in the graphic above. Landsat 8 satellite imagery , the Freshwater Data Atlas from the Government of British Columbia , the Canadian Digital Elevation model, and the Daily Surface Weather and Climatological Summaries were all accessed from online sources.
We then analyzed all the data, using a variety of computer programs, including ArcGIS Pro , ENVI , and RStudio . This allowed us to come up with final values for our Overall Habitat Suitability Index, for both winter and summer.
Results
We classified the landscape into various landcover categories. You can see that there is a lot of treed areas, quite a bit of non-vegetated (rock and ice), with willows, shrubs, and grasses along the river valley.
Grassland and shrubs provide the best habitat for bison. You can see a group of bison near the trees in this picture.
This map shows the distance to water in the study area. For the life of me, I can't get this map to work. Importing rasters is a pain.... And where is the legend???? I tried to change the projection to Web Mercator and it put me in Nigeria!
Swipe the bar from left to right to see the difference in Habitat Suitability Index in summer (left screen) and winter (right screen). Notice that the scales are different - the maximum value in winter is only 9! In summer, almost 70% of the area has a HSI value of 6 or greater, whereas only 17% meets that value in winter.
Bison wade through the snow. Photo by Jim Peaco, National Park Service.
Conclusions
Our habitat suitability model shows that there is significant habitat of sufficient quality to support a population of plains bison year-round in the Halfway River drainage.
Available habitat in winter is considerably less, especially in years with high snowfall. Areas with acceptable winter habitat is limited to the river bottom and the far eastern section of the study area. Despite this, we feel that the area that would be acceptable as habitat is sufficient for a considerable population of bison.
The future
The current study provides good estimates of relative suitability. Perhaps a more relevant consideration, though, is absolute suitability. That is, how many bison can the area carry without causing significant habitat degradation. To obtain this estimate, we would need to acquire an estimate of forage production which would be by intensive sampling of plots throughout the entire region or by using predictive models, based on spatial covariates including landcover, topography, and vegetation indices.
In our next phase of the study we would be interested in expanding the analysis to other locations and further develop models for carrying capacity. These results could be used for management of the herd, ensuring it’s continued health and well-being.
Additional information
If you are interested in learning more, here is a link to a scientific article that did a similar study for habitat in Banff National Park.
Another website worth checking out is the following from Parks Canada. Based on the above study, in 2018, 31 bison were released into Banff National Park. Follow their story here:
Finally, this is a document produced by the British Columbia Ministry of Environment, Lands, and Parks on Bison in British Columbia
