The Impacts of Mountain Biking on Wildlife and People

Michael J. Vandeman, Ph.D.

March 27, 2007

It is obvious that mountain biking is harmful to some wildlife and people. No one denies that. Bikes create V-shaped ruts in trails, throw dirt to the outside on turns, crush small plants and animals on and under the trail, increase levels of human access into wildlife habitat, drive other trail users off the trails and out of the parks, and teach young people that the rough treatment of nature is acceptable. Because land managers were starting to ban bikes from trails, mountain bikers decided to try to shift the battlefield to science, and try to convince people that mountain biking is no more harmful than hiking.

The appropriate tool for comparing the impacts of two activities, such as hiking and mountain biking, is the experimental study. One selects two trails, as identical as possible, and applies hiking to one and mountain biking to the other, and then measures the variable of interest (e.g. erosion), while trying to control all other factors (e.g. the weather). IMBA has collected all the research they could find that seemed favorable to mountain biking (see http://www.imba.com/resources/science/index.html). I reviewed that research, and one other experimental study (see http://home.pacbell.net/mjvande/scb7). While the authors claimed to show that mountain biking and hiking have the same impacts, they didn't report their results accurately.

For example, they said that both activities caused the same amount of erosion, but they forgot to multiply the amount of erosion by the total distance traveled (mountain bikers typically travel several times as far as hikers, thus causing several times as much erosion). Some other defects that biased their conclusions are: riding much more gently than normal mountain biking; not measuring soil displaced sideways; and ignoring research or results unfavorable to mountain biking. One researcher even told the hikers to approach desert bighorn sheep, while instructing the bikers to ride by without stopping! A study (by M. J. Wisdom, et al) that found mountain biking to have greater impacts on elk than hiking has been ignored by IMBA.

D. D. White et al did a "survey" study (reviewed at http://home.pacbell.net/mjvande/white) which claimed that mountain biking has the same impacts on soil as hiking. A survey study simply takes measurements of existing conditions, and tries to draw inferences from them. For example, one might measure tread depth on hiking trails and compare it with that on mountain biking trails. Nothing useful can be concluded from such a study: there's no way to know if the differences were due to hiking vs. biking, or to differences in terrain, weather, soil type, amount of use, trail construction or maintenance, hikers walking on the "bike" trails, bikers poaching the hiking trails, etc.! White collected no data on hiking, but used figures from other parts of the world! Jeff Marion's research (reviewed at http://home.pacbell.net/mjvande/marion) is likewise based on a survey design, and thus of no value in such comparisons.

There is a trend for advocates of mountain biking to publish articles on mountain biking impacts that purport to be scientific studies, but in fact are designed and intended to promote mountain biking by minimizing its impacts and by drawing conclusions that don't follow from their data. The danger is that people will quote such conclusions out of context, as if they were supported by the research, which they are not.