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Two Views on the Environmental Impacts of Trails

The following two articles present personal opinions in our continuing forum on the impacts of trail recreation. Neither the Trails Program nor the State of Colorado endorse any particular viewpoints, and we welcome comments or articles on this topic from our readers.

Biased Biology Exaggerates Impacts of Trails on Wildlife

By Suzanne Webel, Boulder County Trails Coalition

A few vocal preservationists appear to have convinced the Open Space staff and the Board of County Commissioners that even a small number of trail users causes vast and irreversible damage to the entire ecosystem, and that any human impact on "nature" is unacceptable. We disagree with the research and we disagree with both conclusions.

Proponents of the "Open Space is for habitat preservation only" philosophy are fond of citing bird studies conducted on City of Boulder Open Space which indicate that some birds and their nests are found in greater abundance with increasing distance from some trails. Therefore, say these preservationists, we can extrapolate from the bird studies to all wildlife, and to all ecosystems, and therefore we can say that all trails are "bad" because they fragment the habitat for all wildlife.

"Wait a minute!" say the trail advocates. Closer examination of the bird studies reveals that the vast majority of bird species (84%) don't "care" about trails, and of those that do, the detrimental effect of the trail is vanishingly small (2%). Taking City Open Space bird species as a whole, the overall trail effect is only three tenths of one percent, or 0.32% (16% x 2%). We're not denying that a subtle trail effect exists for some species; we're merely trying to keep "biased biology" from being blown out of proportion. How much recreational access should be given up to realize a three-tenths-of-one-percent increase in possible wildlife habitat?

So what effect do existing trails actually have on County Open Space? If every trail were viewed as an environmental catastrophe 100 feet wide, over which no bird dared fly and no mouse dared cross and on which no blade of grass dared grow, this "trail effect" for each jurisdiction can be calculated. Phrased another way, if all BCPOS users were restricted to existing designated trails only (60 miles) and the trail effect were 100 feet wide and 100% for every trail, every day, year round, trail users would be "devastating" a whopping 1.3% of all Boulder County Parks and Open Space lands (81 square miles).

But trails are not environmental catastrophes, of course, so if we multiply the trail effect (0.32%) by the percentage of Open Space lands affected by trails (1.3%), we conclude that Open Space trail users may actually reduce the overall integrity of Open Space lands by less than four thousandths of one percent (0.0041%). The quality of the Open Space environment for the birds and the bunnies is, therefore, 99.9959% of what it would be with no trails.

Phrased another way, because of trail use there may statistically be one less bird successfully fledged on Boulder County Parks and Open Space out of every 24,390 successful fledglings.

In addressing the appropriate balance between passive recreation and environmental preservation, we believe these statistics support our responsible requests for more trails on Boulder County Parks and Open Space. Despite all the emotional rhetoric, trails have truly minimal environmental impact.

Outdoor Recreation and the Environment: Questions, Solutions
By Roz McClellan, Rocky Mountain Recreation Initiative

Outdoor recreation is one of the most transformative forces sweeping the Rocky Mountain west. For decades outdoor recreation has been viewed as an ally of land conservation. Initiatives such as the Land and Water Conservation Fund, Great Outdoors Colorado, and the Appalachian Trail were founded on the twin goals of conservation and recreation. With escalating growth of population, income, technology and mobility, however, recreation and conservation may not be as compatible as they were in the past.

Recreational trails are one example of the recreation phenomenon. Trail expansion into the backcountry is the latest in a century and a half of landscape alteration, starting with mining, grazing, logging, roading and continuing more recently with urban development. Human impacts on the land until now have been limited by topography. Places too steep for cars and logging roads remained relatively natural until the early 1980's. Now, "go-anywhere" technologies are extending human influence into remote, inaccessible places never breached before.

Mountain bikes, ATVs, snowmobiles, snowcats, sophisticated rock climbing and caving equipment, GPS, infra-red scanners, cell phones, in-line trail roller blades and challenge-equipped jeeps know no barriers. They have the potential to saturate the landscape with human presence. These new recreational technologies have the effect of transforming former barriers to human access, such as cliffs, steep slopes, and rivers into mere challenge opportunities.

Another aspect of new trail technologies is their high-speed nature, which extends their range beyond that of traditional hiking and horse activities. Whereas a hiker or horseman might cover ten miles in a day, mountain bikes, snowmobiles and off-road vehicles can travel up to thirty or more miles in a day. Many more acres of habitat are thus affected by a given recreational experience. Not only is the land shrinking under these mechanical uses, but nature is viewed less as something to contemplate than as a blurry back drop to high-speed gravity thrills.

Recreational trail expansion is affecting wildlife as well as the human backcountry experience. Many species of birds and mammals need large undisturbed tracts of land for breeding and habitat security. There is a misperception that because bear and elk are sometimes seen near roads and trails they are adapted to this kind of habitat fragmentation. In fact, while large mammals may forage near roads and trails, foraging is only one of their life-cycle needs. Reproduction for many species, including song birds and cavity nesting birds, requires the undisturbed interiors of large habitat blocks.

Over time, these species' viability can be affected by the habitat fragmentation caused by roads and trails. Studies show that trails affect the reproductive success and abundance of bird species such as brown creepers, vesper sparrows, solitary vireos, Townsend solitaires, and some types of hawks. These species are sensitive to the kinds of changes in micro-climate, small predators, and weeds which go along with trails.


From a land management perspective, recreation trail expansion represents a challenge not presented by previous commodity uses. Expanding as they often do through social use, trail systems on public lands are rarely initiated by a formal NEPA (National Environmental Policy Act) process. User-created trail systems, whose impacts taken together would be significant enough to trigger a NEPA evaluation, are often ratified after the fact by public land managers in a process analogous to approving a "user-created" timber sale.

The Medicine Bow National Forest, for example, has thousands of miles of user-created motorized routes, pioneered by motor bikes, snowmobiles and ATVs, which it has no means to control, monitor, or evaluate. The Forest could declare these routes "unauthorized" and put them into some kind of "study" status, until site specific analysis was conducted to determine whether they should be added to the travel system. Instead, the Forest is allowing use to continue and the routes to become permanently established with no environmental analysis.

On the Boulder Ranger District, mountain bicyclists are constructing unauthorized mountain bike trails in the woods and threatening to continue the activity unless the Forest Service approves more mountain bike trails.


Solutions to unchecked recreation expansion are emerging in several forms. In addition to the collaborative decision process described above, education and public cooperation are a big part of the solution. Recent polls in Colorado show that the public rates wildlife and habitat protection as its top priority, higher than trail maintenance, developed recreation, youth opportunities and other priorities. These public preferences are not just theoretical. Case studies from Jefferson County Open Space show that with adequate education, the goodwill evidenced in these polls can be translated into behavior changes. When wildlife is at stake, Colorado citizens may be willing to forego unrestricted access to nature.

The second solution is the gradual instituting of a landscape perspective in trail planning. Until recently, trails were viewed as linear corridors independent of the spatial patterns they form across the landscape. Increasingly, trails, like roads, are being understood as potentially contributing to habitat fragmentation by breaking up habitat into smaller patches.

Better planning of trails will assure that trail development is balanced with preserving the region's natural heritage. The Colorado State Trails Program is playing a leadership role in spreading the concept of trail planning to towns, counties, and federal agencies around the state. The funding this program administers can provide a powerful incentive for ecologically-based trail planning.

Another solution is the physical design of trails and other recreational facilities. Trails, trailheads, campgrounds and other infrastructure can be designed so as to mitigate the impact of human activity on the surrounding landscape.

Yet another solution is managing ourselves, for example, via regulations based on capacity determinations of how many people the land can hold. Recreation capacities may be established based on: a) user experience, or b) habitat effectiveness models. For example, people experience a loss of solitude after a certain level of trail encounters is exceeded. And elk tend to avoid areas with road densities of more than one mile per square mile. To maintain effective elk habitat or to retain opportunities for solitude, agencies are turning to permits and zoning schemes such as the Forest Service's Recreation Opportunity Spectrum, which allocates land use along a spectrum of uses from primitive wilderness to urban interface zones.

Yet another solution will be the deliberate creation, through engineering and landscaping, of new recreational play areas in already disturbed areas (for example, restoring gravel pits or roadside ATV play areas). Where feasible, this could provide an alternative to disturbing large, evolutionarily-intact blocks of habitat.

October 1999

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