In 2013, Parks Canada published a first draft plan to reintroduce plains bison to Banff National Park. This project was supported by the reasons that bison play a key role in the ecosystem and function as a food resource for predators and scavenger. Plains bison play a key role in prairie ecosystems. Through their grazing and wallowing combined with naturally occurring fires, plains bison have a disproportionally large impact on their environment. However, the role bison play in Banff National Park is likely to be of minor importance. In fact, the reintroduction of plains bison may even harm the Banff ecosystem through enhanced seed dispersal of exotic species and fragmentation through bison- fencing. It is concluded that if bison will be reintroduced, more research is needed, first, on the impact of bison to the Banff ecosystem and second, on the impact of bison fencing on the movement of other wildlife. Also, Parks Canada should be willing to cancel the project if the ecological costs outweigh the benefits.
During the writing of this article, Parks Canada launched a first draft plan to reintroduce plains bison to Banff National Park (NP), Alberta, Canada. The vision is “Restoration of a wild, free- roaming bison population in Banff National Park in a way that that supports ecosystem integrity, enriches and is compatible with other visitor experiences, facilitates cultural connections with the landscape and wildlife, and enhances learning and stewardship opportunities, both in the park and from afar” (Parks Canada 2013).
One wonders why plains bison should be reintroduced to Banff NP which lies in the far northwestern edge of their historical range. Parks Canada mentions several reasons for that which I will present in the next paragraph.
3. What are the reasons for Parks Canada to reintroduce Bison?
Parks Canada (2013) names many reasons why plains bison should be reintroduced to Banff NP. They tell about a cultural reconnection, the value of watching these charismatic animals in the wild and other reasons. However, in this paper I will focus on the ecological reasons for reintroducing plains bison.
According to Parks Canada (2013) plains bison was historically present on the eastern slopes of the Continental Divide which includes the area of Banff NP. Bison is supposed to have been the dominant herbivore in Banff NP and have played a key role in the ecosystem (Parks Canada 2013). Through their grazing, wallowing and trampling, bison helped to create and preserve meadows, grasslands and other open habitats (Parks Canada NA, Parks Canada 2013). This, in turn conserved the species depending on these open habitats (Parks Canada 2013). As they are big animals, plains bison were a significant food resource for predators and scavenger (Parks Canada 2013).
A dead bison carcass has a substantial impact on the surrounding soil and plant community (Parks Canada 2013). Parks Canada (2013) sees the reintroduction of bison as a step towards the full restoration of Banff NP’s biodiversity and natural processes.
4. Key role of plains bison in the prairie ecosystem
Indeed there is literature stating that bison is a keystone- species supporting the arguments of Parks Canada (2013). According to Power et al. (1996) a keystone species is a species that has a disproportionally large impact on its community or ecosystem relative to its abundance.
In the following, I will outline arguments that support the thesis of bison being a keystone species in prairie ecosystems.
In 1987, 30 plains bison were reintroduced to the unplowed Konza tallgrass prairie in Kansas and Utah (Knapp et al. 1999). The herd of bison was not actively managed, only prescribed spring fires were applied to the site to mimic natural fire disturbance (Knapp et al. 1999). Within five years the herd grew to a size of 200 individuals that allowed a good insight into the impacts of bison on their ecosystem.
It was shown that bison graze either in distinct intensive patches or in extensive grazing lawns (Knapp et al. 1999). Bison revisited their grazing sites repeatedly throughout the year which creates relatively sharp edges between grazed and ungrazed vegetation (Knapp et al. 1999). Bison tend to focus the dominant C4 grasses and avoid forbs and woody plants, since they are primarily graminoid feeders (Peden et al. 1974; Fahnestock & Knapp 1993).
Therefore, the dominant C4 grass species were lowered in abundance which indirectly supports the growth of the subdominant plant species (Knapp et al. 1999). Without bison grazing, the dominant C4 grass species increased in abundance relative to C3 grass species, forbs and woody species (Gibson & Hulbert 1987) which caused a significant decline in plant species diversity (Knapp et al. 1999).
Research in Konza prairie also investigated in the relationship of bison grazing and fire. Without bison grazing and increased frequency of fires, plant species diversity dropped because the dominant C4 grass species such as big bluestem (Andropogon gerardii), Indian grass (Sorghastrum nutans), switchgrass (Panicum virgatum) and little bluestem (Andropogon scorparium) were favoured through this disturbance pattern (Collins et al. 1995).