A Critique of "A Comparative Study of Impacts to Mountain Bike Trails in Five Common Ecological Regions of the Southwestern U.S." (White et al 2006)
Michael J. Vandeman
"If a journalist writes an erroneous article, you can send a letter to the editor. If a businessman does not know what is going on, he will probably lose money and his job as well. But, oddly enough, academics can make mistakes, gross and manifest ones, time and again, and get away with it. For they operate on the basis of peer review. Once the overall community has been converted to a given position, they regularly coopt members with the same views. And thus there is no one to criticize them. Indeed, the critics are neatly kept out of the academic establishment by those who are already in it." Jon Woronoff, Japan as Anything But Number One, p.288
I am concerned about a trend I have noticed 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 White et al (2006) study is a good example of this genre. The authors claim to show that mountain biking impacts (specifically, erosion) are no worse than those of hiking. However, in drawing this conclusion, they neglect to state clearly the question (hypothesis) they are trying to answer, rely on studies that are faulty, misinterpret other studies, make subjective judgments where science requires statistics, and use a research design that is not capable of supporting the conclusions they draw. The danger is that people will quote such conclusions out of context, as if they were really supported by the research, which they are not.
numbered my points to make it easier to coordinate their reply with my
comments. I would like the authors to respond to each point using the same
numbering scheme, so that I can see that they have addressed every point.
1. Are the authors mountain bikers? They seem to be promoting mountain biking -- trying to make it seem environmentally acceptable.
2. Why does the abstract and paper make comparisons between hiking and mountain biking impacts? They apparently didn't collect any data that would allow them to make such a comparison. In fact, the only way to make such a comparison is with an experimental design, not a survey, as they have done. It is logically impossible to draw any useful conclusions from a design that includes measurements taken at only a single point in time. The data (trail width and depth) provide no way to distinguish between mountain biking impacts and the effects of trail construction, trail maintenance, wind, rain, hiking, animals, or any other factors.
3. The comparison of mountain biking vs. hiking impacts seems to rest on three bits of information: Wilson and Seney (1994), Thurston and Reader (2001), and a vague, non-statistical judgment about their measurements being "similar" to those of hiking trails. The Wilson and Seney study was discredited by Vandeman (2004), because they didn't measure erosion accurately: they dripped water on the trail and collected and weighed the solids carried into the collecting pan. This only takes into account very fine particles able to be transported by such "artificial rain"; it ignores all of the larger particles dislodged by feet or tires. The Wilson and Seney study thus provides no useful comparison between hiking and mountain biking impacts.
4. They also misrepresented Thurston and Reader's results. Actually, Thurston and Reader found that after 500 passes, mountain biking had greater impacts on plants than hiking. It doesn't take long to accumulate 500 passes. Some trails will receive that amount of traffic (250 visitors) in a day or two. So this study actually provides no support for White et al's claim that hiking and mountain biking impacts are "comparable" (whatever that means).
5. The authors
provide no other quantitative, statistical comparison between hiking and
mountain biking impacts. The only way to do that would be to do an experimental
study, where all factors except hiking vs. mountain biking are controlled (in
other words, apply equal amounts of hiking and mountain biking to identical
trails and measure the impacts using before-and-after measurements).
6. Their estimate
of the number of mountain bikers ("21% of the American public")
seems grossly exaggerated. I think they need to find a more reliable source for
7. They make claims
about the benefits of mountain biking. This seems out of place in a scientific
paper, especially since they provide no evidence for any such (net) benefits.
Such claims are usually biased by tallying alleged positive benefits without
subtracting the harm caused by mountain biking (e.g. accidents, environmental
damage, wildlife impacts, and driving other trail users off of the trails).
8. They claim
"management actions that limit access can be controversial and raise
issues of equity", but provide no evidence. I'm not aware of any limited
access or issues of equity. Since only bicycles, not people, have ever
been restricted, I don't see how they can make such a claim. In fact, it is very
unlikely that there are any equity issues, since it was already determined by a
federal court that bikes may be banned from trails (see http://mjvande.info/mtb10.htm).
9. I'm glad they mention "questionable studies". There are, indeed, a lot of them! But I wonder why they included some of them in their references, such as Wilson and Seney, and presented them without comment, as if they were sound science (see Vandeman 2004). They also misrepresented Thurston and Reader's results, as I explained above.
10. On p.24 they
mention "visitor-related factors", but omitted impacts on other trail
users. I think that that is one of the major impacts of mountain biking. I'm
aware of many parks where mountain bikers have driven other trail users off the
trails and out of the parks.
11. On p.26 they
claim that "the magnitude of ecological impacts attributed to mountain
biking appear to be comparable to those of hiking". "Comparable"
is vague or meaningless as a scientific term. The Earth is comparable to the
Sun (they can be compared). I think that they also misrepresent the implications
of those studies (see Vandeman 2004).
12. On p.29 they
mention "user-created" trails. Why use a euphemism, in a scientific
paper? Those trails were built illegally. The authors only add to the
impression that their paper is deliberately slanted.
13. They make a good
point on p.36 about trail users having to leave the trail to allow mountain
bikers to pass. This is a good reason to ban bikes from trails: they lead inevitably
to trail widening. But the authors don't suggest banning bikes as an option,
even though it is a very common management tool. This adds to the impression of
14. On p.37 they
claim that "the width and depth" of their trails is
"similar" (not a scientific term, since it is so vague) to that of
Marion & Leung, although their trails averaged 32" wide (median
26") and his median trail width was 17", so theirs was 50% greater.
Why be scientifically precise in some contexts, but totally vague when they
want to advocate for mountain biking? It is scientifically meaningless to compare
trails in different areas, since the differences or similarities could be
caused by many irrelevant factors, such as differences in soil type, kind and
amount of use, management policies, etc.
15. Also on p.37 they
claim that "The findings from our study thus reinforce results from
previous research that certain impacts to mountain bike trails, especially
width, are comparable or less than hiking ... trails". On the contrary, they
presented zero data on the width of hiking trails. In fact, they gave evidence
(see # 13 above) that mountain biking tends to widen hiking trails, by forcing
hikers and equestrians off the trail.
16. They also say
"average width in our study was similar to lower use mountain bike trails
in Australia ... which [were] from 17 in. to 26 in." "Similar"
is not a scientific term. It would appear, on the contrary, that their trails
were much wider than those ones. But as I mentioned earlier, it is meaningless
to compare trails in different areas. There is no way to determine the cause of
any differences or lack of differences.
17. They claim on
p.37 that "mountain biking is likely a sustainable activity on properly
managed trails". What does that mean? They have just documented erosion
and trail widening. Those effects are not "sustainable"; they
constitute environmental damage, in addition to that of other trail users.
They go on to mention several other negative effects of mountain biking
(wildlife impacts and spread of exotic species) that also contradict the idea
that mountain biking is "sustainable". It would appear that they are
bending over backwards to conclude that mountain biking is acceptable.
18. I fail to see
the value of "the introduction of CERs" (Common Ecological Regions).
It seems to have no relevance to policy or management, unless we are going to
prohibit mountain biking in desert areas where trails can't be clearly
delimited. But we already know that trail widening is harmful: it represents
In summary, I was bothered most by the authors' unquestioning acceptance at face value of (or even misrepresenting) some rather questionable studies, and their drawing conclusions not warranted by their data. If they really want to do science, and not just promote mountain biking, I think they should adhere better to what the data tell us.
Actually, it's much easier than trying to slant results. Permit me to tell a little story. I was in graduate school at UCLA, was trying to write a literature-review paper, and was having a terrible time writing it -- until I realized that I was trying to make the results come out the way I wanted them to. When I decided to "just tell it like it was" and let the cards fall as they might, the paper almost wrote itself. It became easy.
Mountain biking is such a contentious issue that there is a great temptation to slant the results to support one's preferred management policy. The result is a lot of questionable studies that don't really further science and don't really help provide sound scientific management of our precious remaining wildlife habitat. I suggest that they first find out what kind of answers are needed (especially by land managers), and then design research specifically to answer those questions, instead of first collecting data, and then trying to see how they can force it to yield the conclusions that they desire.
Thurston, E. and R. J. Reader. 2001. Impacts of experimentally applied mountain biking and hiking on vegetation and soil of a deciduous forest. Environmental Management 27:397-409.
Vandeman, M. J. 2004. The Impacts of Mountain Biking on Wildlife and People -- A Review of the Literature. Available at http://mjvande.info/scb7.htm.
White, D. D., M. T. Waskey, G. P. Brodehl, and P. E. Foti. 2006. A Comparative Study of Impacts to Mountain Bike Trails in Five Common Ecological Regions of the Southwestern U.S. Journal of Park and Recreation Administration, 24:2, 21-41.
Wilson, J. P. and J. Seney. 1994. Erosional impact of hikers, horses, motorcycles, and off-road bicycles on mountain trails in Montana. Mountain Research and Development. 14:77-88.