Column: “Fat Tires and Public Trails”

Rocky Mountain News, May 29, 2007

Argument about mountain bikes goes flat

For years, land managers, hikers and others have argued that mountain bikes shouldn’t be allowed on trails, and for years, a number of the region’s urban trail systems have been all but off-limits to bikers.

There were a number of reasons for the calls to limit fat-tire access, including safety concerns – that bikers might hurt themselves and others – and social conflicts between bikers and people, usually hikers or equestrians, who simply didn’t like to see bikes speeding past them on the trails.

But for years, the strongest argument against allowing mountain bikes on trails was that mountain bikes would accelerate environmental damage on the trails. Recently, though, we have learned that argument largely was wrong.

It has long been clear that any trail use causes some environmental degradation, including vegetation loss and changes, soil compaction and erosion, muddiness and disruption of wildlife. The effects are especially aggravated when trails are poorly constructed and located.

It was not clear, however, that mountain biking caused more damage than other recreational pursuits. Until recently, there had been little empirical study of the relative environmental impacts of mountain biking versus hiking, horseback- riding, off-road vehicles and off-trail uses such as fishing and birding. In the absence of adequate research, land and trail managers tended to err on the side of caution and banned mountain bikes from many of the trails they managed.

But last year, recreation ecologists Jeffrey Marion, a scientist with the U.S. Geological Survey, and Jeremy Wimpey, a doctoral candidate at Virginia Tech University, conducted an extensive review of the current scientific research on the sport’s environmental impacts for Managing Mountain Biking: IMBA’s Guide to Providing Great Riding, a book published by the International Mountain Bicycling Association (which I helped to edit).

The review concluded there is little evidence mountain bikes accelerate environmental problems any faster than other trail uses. In fact, mountain bikes cause no more harm to the trails environment than hikers do, and wreak far less damage than do equestrians and motorized users.

For the review, Marion and Wimpey examined more than 30 studies on mountain biking and recreational trail impacts and divided the research into four broad categories: vegetation, soil, water and wildlife.

The studies reviewed by the two ecologists found while all trail use can cause damage and changes to vegetation, impacts from bikers tend to be similar to those of hikers and generally are confined to the center of the trail.

The same was true for soil loss – mountain biking differs little from hiking in its contribution to ruts and erosion, and equestrians and motorized users have far greater effect. Any type of use on wet trails, however, causes significantly more damage than when soils are dry.

There have been no studies on the specific role mountain bikes might play in watershed degradation, but the science suggests properly designed and maintained trails should minimize trail-related water quality issues caused by all users.

And because bikers usually stay on trail, they tend to have less effect on wildlife than those who travel off-trail more frequently (such as some hikers, birders and fishermen), although bikes do travel farther and cover more ground than typical hikers and therefore have potential to disturb more wildlife.

In fact, Marion and Wimpey say, what the current research suggests is that when it comes to trails, the major issue is not the type of user, but the way the trail is built – the trail’s grade, alignment angle related to the fall line, and soil type. If a trail is sustainably designed and constructed, it should be able to handle bikes, hikers and, in some cases, even horses and ATVs, without significant damage to the environment – beyond the basic potential harm caused by any human traffic in the backcountry.

As more research on the environmental effects of recreation on trails and wildlife comes in, land managers will be able to make better and more informed decisions about what type of activity is acceptable on our trails.

In the absence of a body of peer-reviewed, empirical research, however, we too often end up engaging in speculative and frustrating echo-chamber debates like those that recently have raged in Boulder, where recreation advocates and preservationists continually spar about the consequences of recreational trail use.

Everyone agrees it’s important to practice good stewardship of the trails – but no one really knows what that entails. More studies and reviews of the environmental effects of recreation on trails, like the one Marion and Wimpey conducted for IMBA (, would help ground these emotional debates.