Swarthmore College Environmental Studies

20 April 2006

Trail Trials

Outdoor recreation is an essential element of daily living for many Americans, and the American backcountry, with its abundant trails, is a popular outdoor playground. At present, approximately 200,000 miles of public-use trails sprawl throughout the United States (1). Some of the most common trail uses include motorized “off-roading”, and non-motorized uses such as running, hiking, cycling, and horseback riding. While motorized trail travel may be deemed more damaging to the environment, in actuality non-motorized trail users pose no less of a negative impact. Any type of intense human trail use and expansion results in environmental consequences. This paper will discuss the impact of trail travel (particularly non-motorized travel) by presenting the most common charges against trails, some benefits of trails, and trail planning strategies to reduce trails’ negative impacts on wildlife.

Criticism of trails has both ecologically and socially related bases. In the psychosocial sense, some people may contend that “trails lead from one civilized point to another, imposing a civilizing effect on wilderness, which by all rights and by definition, is the antithesis of civilization” (2). Without arguing about the biological impacts, some people may simply find it unpleasant to see humans intrude upon an untouched natural landscape or to hear whirring off-road vehicles emitting noxious fumes in once preserved natural areas. Since motorized trail users are often louder and larger, a myth exists that they impose a deeper biological threat to wild lands than does foot traffic. However, motorized trail users may cause no more disruption to wildlife habitats than that of hikers, bikers or horseback riders. Explorers on foot are more prone to leave behind their litter, stray off of established trails, leave behind human waste, and generally stay in an area longer, which leaves more time for any of these incidents to occur (3). It is unfair to argue that one type of use is any more detrimental than the other, for when human trail use is frequent enough, each puts some strain on the ecosystem.

Some of the most common attacks concerning the ecologically detrimental effects of trails claim that, like roads, trails fragment previously uninterrupted natural habitats, causing the formation of “biogeographic islands.” The edges of these islands can have negative effects on the biodiversity of native flora and fauna. Some native animal species may not be able to tolerate the new conditions introduced by the trail, such as increased levels of light, wind and human intrusion. Native species in undisturbed habitats are commonly specialists, who can only survive well within a narrow niche. A change in living conditions, however, may be suitable for non-native, usually generalist, animal species. Generalists’ ability to survive in a broad range of conditions allows them to out compete the native wildlife. Native animal species may also avoid the edges of trails, oftentimes due to apprehension of a continual human presence. Trails may even induce a loss of breeding opportunities, should an animal species not dare to venture across a trail at all (2). Loss of biological diversity is a major consequence of habitat fragmentation.

As for flora, the edges of trails provide favorable growth conditions for weeds and other non-native plant species. In blazing a trail, the removal of natural vegetation can increase the amount of rainfall and intensity of sunlight along the trail, and reduce root competition for important nutrients and minerals in the soil (2). Trails also allow for new lines of plant dispersal. Human foot travelers may act as dispersers of non-native plant species, as seeds attached to hikers’ shoes, horses, or bicycle tires are frequently transported into new habitats. Invasive plant species, like invasive animal species, are usually generalists who can survive in a wide range of conditions. Trail edges permit rapid growth and reproduction of these invaders. Exotic plants can quickly disperse further off-trail, whether by natural dispersal or by humans exploring off-path, and become a competitive threat to native species throughout the entire community. By taking control of the energy and nutrients in the area, non-native plant species can out-compete native flora.

Trails can also degrade the soil in an area. In a study of wild lands in the Rocky Mountains, David Cole found that trail construction may modify an area’s slope angles and drainage conditions (4). Soil erosion may induce soil quality degradation. Furthermore, continual human foot travel on trails leads to trampling. Trampling compacts soil to such a high degree that very few plants can manage to grow. Compaction damages plants’ roots and lowers soil aeration, water content and structure (5). Cole’s study provided evidence of this, as the heavily trampled center of a trail was bare, with vegetation cover gradually increasing away from the trail’s centerline.

Despite the negative ecological impacts trails may impose upon wildlife habitats, trails have benefits as well. While it may be the most eco-friendly to fully restrict human use of wild lands, such a control is unpopular and unfeasible. Humans have an intrinsic attraction to nature, and are bound to explore whether a trail exists or not. Established trails can therefore be beneficial in that they confine human use and trampling to a narrow pathway, and they can route humans away from very sensitive wildlife habitats. In the social and political spheres, trail users, such as today’s increasing number of “mountain bicyclists could prove to be for the environment what backpackers became in the 1960s and 70s, the core foundation for expansion of environmental ethics” (2). Such users may benefit wild lands as many of them are proponents of wild land protection and responsible trail use.

Although it is inevitable that trails subject ecological communities through which they cut to some degradation, trail developers can employ better trail planning strategies as a means to reduce the trails’ impact. In selecting a site for a new trail, trail developers should consider the site’s history. Trails can have regenerative effects on wildlife in some areas. The species composition of wildlife community in an area is often dependent on disturbances that have occurred within the area. A disturbance is any event that affects the status quo–species composition and stage of succession–of an ecological system. For instance, trail builders may best choose a site wherein a disturbance has recently caused the loss of several species. A trail, with its edges, may promote the regeneration of biodiversity. On the other hand, areas subject to a loss of biodiversity by trail construction are those sensitive habitats which are undisturbed and species-rich and should be avoided as much as possible. To further minimize the impact of trail edges, developers should attempt to coordinate trail edges with other already existing biogeographical edges so as not to construct new ones.

In terms of administering human impact, trail builders may employ screening. Screening is most effect in areas of dense vegetation, as the vegetation blocks humans from the sight of animals while still allowing for humans to see the habitat. Developers should also ensure that trail user receive an satisfying enough experience of wildlife sights, so that the likelihood of users adventuring off-trails is low. To the highest degree possible, trails should avoid extremely sensitive wildlife habitats, which are commonly found in riparian areas. Since the likelihood that people will attempt to catch a glimpse of water habitats whether a trail provides access to them or not is high, trail builders may choose to route trails close to water habitats only at points where their impact is negatively minimal or positively regenerative. Trail builders may also consider reducing trail density or constructing dead-end trails in areas of high sensitivity so that human foot traffic remains low. Most important is the task of educating the general public about wildlife and lands and responsible trail use.


(1) American Trails. <http://www.americanhiking.org>
(2) “Two views on recreation and wildlife.” <http://www.hccaonline.org/page.cfm?pa geid=2070>.
(3) “Environmentally responsible off pavement travel.” <http:/home.earthlink.net/ ~cyberkiwi/environment/index.html>.
(4) Cole, David N. 1978. Estimating the susceptibility of wildland vegetation to trailside alteration. The Journal of Applied Ecology. 15: 1.
(5) “Planning trails with wildlife in mind.” <http:/parks.state.co.us/home/publications>.

Swarthmore College ES Contact Swarthmore ES Contact Webmaster Bon Appetit H2Obsession Trail Trials The Roman Baths email me