Snowmobiles Stress Wildlife In Winter

by Jacob Smith, Biodiversity Legal Foundation, from The Road-RIPorter 1.4

The majority of motorized recreation research has focused on the impacts of summer recreational vehicles rather than snowmobiles, perhaps because thick blankets of snow seem to offer protection against their harmful impacts. In fact, snowmobiles pose a serious threat to ecosystem integrity and biological diversity. Below we discuss three categories of snowmobile impacts: (1) direct impacts of exposure and harassment, (2) indirect and cumulative impacts of exposure and harassment, and (3) impacts associated with snow compaction.

The direct environmental impacts of snowmobile use include harm to wildlife, vegetation and soils. Snowmobiles harass wildlife, causing increased metabolic rates and stress responses. During the winter months, when many animals are already burdened by increased levels of stress due to low temperatures, inclement weather, and reduced food supply, wildlife are especially vulnerable to this harassment. Snowmobile use can also cause disruption in movement patterns, making it more difficult to locate reliable food sources. These impacts are best understood and documented for ungulates (Cain et al. in preparation, Greer 1979, Moen et al. 1982, Parker et al. 1984, Severinghaus and Tullar 1975); nevertheless, many other wildlife species suffer the same sorts of direct impacts from exposure to and harassment by snowmobiles.

Snowmobile use can cause significant damage to exposed and unexposed vegetation. Abrasion and breakage of seedlings, shrubs, and other exposed vegetation is common (Neumann and Merriam 1972, Rongstad 1980, Ryerson et al. 1977). Similarly, shallow roots and rhizomes can be crushed or otherwise damaged. Especially on steeper slopes, and particularly when snow levels are low, snowmobile use can lead to considerable soil erosion. Increased sedimentation and turbidity, for instance, can occur both in the immediate area and throughout the watershed (Aasheim 1980).

The accumulations of snowmobile exposures over the course of a winter or several seasons can result in significant long-term wildlife displacement and expanded home ranges, increasing winter stresses and energy expenditures. As a consequence, wildlife (especially larger mammals such as grizzly bears, elk, and bighorn sheep) often suffer increased winter mortality in areas where snowmobiles are used, even in low intensities (Berwick 1968, Bury 1978, DeMarchi 1975, Dorrance et al. 1975, Neumann and Merriam 1972).

Similarly, repeated snowmobile use can lead to changes in plant density and species composition and set back seral stages (Aasheim 1980, Wanek and Schumacher 1975), and the associated loss of vegetative cover generally leads to increased soil erosion (Montana Fish, Wildlife and Parks 1993).

Snowmobile-induced snow compaction is implicated in numerous, often overlooked environmental impacts. For instance, snow compaction can cause considerable below-surface vegetation damage (Neumann and Merriam 1972). Significant reductions in soil temperatures may also result from snow compaction (Aasheim 1980, Rongstad 1980), retarding both soil microbial activity and seed germination (Keddy et al. 1979), and these impacts may be exacerbated by compaction of the underlying soil layers.

Snow compaction is also responsible for numerous and severe impacts to wildlife, especially small mammals that depend on subnivean spaces (the spaces between the snowpack and the ground surface) for winter survival. Compaction lowers subnivean space temperatures, which in turn leads to increased metabolic rates, and thus, increased mortality; in some cases movement is restricted to the point of asphyxiation. When snow is compacted, ungulates must work harder to dig for vegetation (Fancy and White 1985), and the mobility of wildlife such as snowshoe hare and red fox is impaired (Neumann and Merriam 1972). Furthermore, the imperiled lynx is consistently outcompeted by the more prevalent coyote and bobcat when it loses its advantage in deep, uncompacted snow (Koehler and Brittell 1990, Ruediger 1994).

Finally, it is important to note that because most of the snow compaction occurs on the first snowmobile pass, even minimal use of any area can cause considerable damage (Aasheim 1980, Gabrielson and Smith 1995, Keddy et al. 1979).

There are, of course, numerous additional impacts not described here. Air quality can be substantially impaired by snowmobile emissions. Snow compaction often retards melting of snow and thus leads to muddy trails and roads, which are then highly susceptible to significant damage and enlargement. For the same reason, snow compaction can lead to altered melting and discharge regimes, further increasing soil erosion (Montana Fish, Wildlife & Parks 1993). The sight and smell of snowmobiles can be disturbing to humans as well as to wildlife. By virtue of the speed at which they travel and the air pollution they create, snowmobiles effectively displace many non-motorized users.

Despite claims to the contrary, then, snowmobiles constitute a substantial environmental threat. Although much research is still needed, a considerable body of evidence documenting snowmobile impacts can be effectively used to pressure resource managers to develop responsible land use policies.

Bibliography

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