The Effects of Mountain Biking on Wildlife and People --
Why Off-Road Bicycling Should be Prohibited
Michael J. Vandeman, Ph.D.
May 31, 1997
Mountain biking is a relatively new sport. According to a
mountain biking (MTB) web page (http://www.mtb-bike.com
commercial Mountain Bike evolution didn't start until 1974 and its
first production bikes didn't appear in stores until about 10 years
later". (Lower gearing, fat, knobby tires, sturdier construction, but
particularly the sealed bearing -- which could be ridden in dirt
without getting destroyed -- are what made "mountain" (off-road)
bicycling possible.) Partly for this reason, and partly because the
MTB is, from one point of view, just a special case of an ORV
(off-road vehicle), environmentalists and scientists have been slow to
study and recognize the special threat that the mountain bike
represents to wildlife. Although there are many studies of ORVs, I am
not aware of any solid scientific studies specifically on MTBs and
their effects on wildlife.
To most environmentalists, bicycles have always been the
epitome of good. We are so used to comparing bikes to cars, that it
never occurred to us that the bicycle would be ever used for anything
bad. Indeed, replacing motor vehicles with bicycles deserves our
adoration. But anything can be used for good or evil, and using bikes
to expand human domination of wildlife habitat is clearly harmful.
Human beings think they own every square inch of the Earth,
and that they therefore have the right to do what they want with it.
This is, of course, absurd. It is also the reason that we are losing
species at an unforgivable rate: we have crowded wildlife out of its
habitat. Even in our parks, where we have vowed to protect wildlife,
it is not protected from hikers, equestrians, park "managers",
firefighters, mountain bikers, airplanes, helicopters, cars, roads,
concessionaires, or biologists. Thus, the primary reason that mountain
bikes are harmful to wildlife is that they, like other technological
aids (cars, skis, rafts, rock-climbing equipment, etc.), make it much
easier for people to get into wildlife habitat.
(Sadly, most people have forgotten that the only thing that
makes parks worth visiting is the wildlife that live there: it is
precisely the wildlife (and paucity of humans) that make a park a
park. Without wildlife (i.e., all nonhuman, nondomesticated species --
plants as well as animals), the parks would be boring piles of bare
First and most obvious, mountain bikes kill organisms that
live on and under the soil: "When it comes to pure recreational
destructiveness, ... off-road vehicles (ORVs) far surpass powerboats.
... It is a rare environment indeed where a vehicle can be taken
off-road without damage. ... Standard ORVs with their knobby tires are
almost ideal devices for smashing plant life and destroying soil. Even
driven with extreme care, a dirt bike will degrade about an acre of
land in a twenty-mile drive. ... Not only do the ORVs exterminate
animals by exterminating plants, they attack them directly as well.
Individual animals on the surface and in shallow burrows ... are
crushed. ... One great problem with ORVs is that they supply easy
access to wilderness areas for unsupervised people who have ... no
conception of the damage they are doing" (Ehrlich and Ehrlich,
pp.169-171; emphasis added). (Although mountain bikes were hardly
known when this was written, it is obvious that the same applies to
Recently, one of the largest Alameda whipsnakes (a California
threatened species) ever found was killed by a mountain biker in Black
Diamond Mines Regional Preserve near here. Others have been killed on
other East Bay regional parks. Kathryn Phillips in Tracking the
Vanishing Frogs described how ORVs crossing creeks crush toads and
their eggs (both buried in the sand). Bikes are generally ridden too
fast to avoid killing small animals. Obviously, the animals didn't
evolve in the presence of mountain bikes, and can't be expected to
deal very effectively with such quiet, fast-moving objects. Even
hikers can kill small animals, if they aren't careful. The one time I
went to look for an Alameda whipsnake, I almost stepped on one, which
was lying in grass growing in the trail, and didn't move until I had
almost stepped on it.
Soils are extremely complex communities of living organisms.
They sometimes are very fragile and once destroyed take decades to be
recreated (e.g. desert cryptogamic soil). Soil destruction is hastened
by acceleration (braking, speeding up, climbing, and turning, which
apply horizontal forces to the soil), by tire lugs, which break the
surface, and by water, which softens the soil and makes it easier to
In the Golden Gate National Recreation Area (GGNRA), "park
officials noted serious erosion problems on certain steep narrow
trails and determined that restricting bicycle use would slow such
erosion. [They] noted that on narrow trails bicyclists passing other
users would either leave the trail or force the other users off the
trail to the detriment of off-trail vegetation and wildlife. ...
Downhill bicycle travel on steep slopes is usually accompanied by
braking and often by skidding which tends to push dislodged surface
gravels into ditches, water bars, and drains. Heavy bicycle use on
steep trails usually requires that these ditches, water bars, and
drains be cleared more frequently than those used by hikers and
equestrians only. ... Park staff and visitors reported that bicyclists
on these ... trails often skidded to control their speed, slid off of
trails on sharp turns, or cut across off-trail areas at certain
'switch-backs'" (Bicycle Trails Council of Marin v. Bruce Babbitt).
Mud containing seeds and spores sticks to bike tires, thereby
often carrying species of plants into areas where they had not existed
(becoming "exotics"). This is worsened by the fact that bicycles
travel long distances, and are often carried to distant locations
(sometimes even foreign countries) by motor vehicle. It is well known
that such exotic species can cause havoc when introduced into new
Most of us were raised to believe that "non-consumptive"
recreation is harmless to wildlife. We are taught to enjoy ourselves
in nature, guilt-free, as long as we don't directly harm wildlife.
However, recent research, and the huge scale of current recreation
activities, have discredited this idea. "Traditionally, observing,
feeding, and photographing wildlife were considered to be
'nonconsumptive' activities because removal of animals from their
natural habitats did not occur.... nonconsumptive wildlife recreation
was considered relatively benign in terms of its effects on wildlife;
today, however, there is a growing recognition that wildlife-viewing
recreation can have serious negative impacts on wildlife" (Knight &
In other words, the mere presence of people is often harmful
to wildlife, and the more, the worse. "The notion that recreation has
no environmental impacts is no longer tenable. Recreationists often
degrade the land, water, and wildlife resources that support their
activities by simplifying plant communities, increasing animal
mortality, displacing and disturbing wildlife, and distributing
refuse" (ibid, p.3) "Recreational disturbance has traditionally been
viewed as most detrimental to wildlife during the breeding season.
Recently, it has become apparent that disturbance outside of the
animal's breeding season may have equally severe effects" (p.73)
"People have an impact on wildlife habitat and all that depends on it,
no matter what the activity" (p.157); "Perhaps the major way that
people have influenced wildlife populations is through encroachment
into wildlife areas" (p.160). "Outdoor recreation has been recognized
as an important factor that can reduce biosphere sustainability....
Indeed, recreational activities, including many that may seem
innocuous, can alter vertebrate behaviour, reproduction,
distributions, and habitats" (p.169).
Knight & Gutzwiller's book contains numerous specific examples
of how these negative effects are created. We may not know what the
organisms are thinking, but the effect is that they die, are forced to
expend extra energy that may be in short supply, become more
susceptible to predation, or are forced to move to less suitable
habitat, losing access to preferred foods, mates, nesting sites, etc.
Since most of us live safely in the midst of plenty, it is hard for us
to understand wildlife's predicament. We are flexible enough to
survive almost anywhere; they are not. Often they have no other place
to live. None of the existing "studies" on mountain biking evaluate
its effects on wildlife. They are usually concerned only with visible
effects on the trail. In Tilden Regional Park, there are three
separate, heavily used mountain biking trails through the middle of
supposedly protected Alameda whipsnake habitat areas!
"Displaced animals are forced out of familiar habitat and must
then survive and reproduce in areas where they are not familiar with
the locations of food, shelter, and other vital resources.... Hammitt
and Cole ... ranked displacement as being more detrimental to wildlife
than harassment or recreation-induced habitat changes.... Densities
... of 13 breeding bird species were negatively associated with the
intensity of recreation activity by park visitors, primarily
pedestrians and cyclists" (ibid, pp.173-4); "off-road vehicles can
collapse burrows of desert mammals and reptiles" (p.176).
Hikers, especially the elderly, have been abandoning their
favorite trails, due to bikers that scare them, hit them, harass them,
and destroy the serenity of the parks. Parks are supposed to be a
refuge from the crush of humanity and the noise, danger, and
artificiality of urban areas. Why bring to our parks the very things
that most people go there to escape?! There is absolutely nothing
wrong with bicycling, in its proper setting (on a road). It is a
wonderfully healthful activity. But wildlife is already in danger due
to loss of habitat (worldwide, one quarter of all animals are
threatend with extinction, according to the IUCN (International Union
for the Conservation of Nature and Natural Resources)). It can't
afford to lose any more. And people have very similar needs for being
in nature. Our elderly are like wildlife, in that they have nowhere
else to go for the experience of nature that they are accustomed to.
By definition, hiking trails are the minimum size necessary
for a person to hike (approx. 18 inches wide), since they are supposed
to have a minimal impact on the environment. They aren't wide enough
for a bicyclist to safely pass a hiker or another bicyclist. Mixing
bikers and hikers is dangerous for both. In fact, mountain biking is
also dangerous for lone riders, since hiking trails don't follow a
predictable pattern and have very short sight distances (the distance
that one can see ahead on the trail). Emergency room doctors report
that a large percentage of mountain bikers incur serious accidents.
"The record includes hundreds of letters from park users
recounting stories of collisions or near misses with speeding or
reckless bicyclists on all kinds of trails but particularly on steep
and narrow trails. Hikers and bird watchers repeatedly told how they
have been forced off of trails by speeding bicycles and how they have
had their peace and solitude on the trails interrupted by bicycles
that -- because they are quiet and fast -- seemed to appear out of
nowhere and be immediately upon the hikers and other users.
Equestrians told how their horses have been startled by speeding or
oncoming bicycles and have become restless, on several occasions even
throwing and injuring experienced riders. Though most users admitted
that the great majority of bicyclists were polite and
safety-conscious, letters from hikers, equestrians, bird watchers,
joggers, and other users also repeatedly recounted incidents of
rudeness, threats, and altercations when they have complained to an
offending bicyclist about dangerous conduct. Park staff also reported
having received such complaints. ... NPS's [National Park Service's]
finding that user conflict and visitor danger would be reduced by
limiting bicycle trail access in GGNRA was supported by ample
evidence. ... Notwithstanding the responsible user, bicycles are often
perceived by other users as a disruptive influence on park trails.
Although most of the few reported bicycle accidents in the park
involve only single individuals, letters and reports from hikers and
equestrians tell of many close calls and confrontational and
unsettling experiences". "No single-track trails [in the Marin
Headlands] were found suitable for bicycle use" (Bicycle Trails
Council v. Bruce Babbitt).
Since bicycles require wider trails, parks now often use
bulldozers to create and maintain those trails, vastly increasing
their impacts. In Claremont Canyon Regional Preserve in Oakland,
California, a new trail was created by means of a "small" (6 foot
blade) bulldozer. But it rolled off the trail and had to be rescued by
a much bigger bulldozer. The existence of bicyclists on trails also
forces park rangers to police the trails using motor vehicles (cars or
motorcycles), since it is the only way they can hope to catch them!
This also increases negative impacts on wildlife.
Children learn mostly nonverbally (by watching adults and
other children). Mountain biking is bad role modeling for them, since
it teaches them that human domination and destruction of wildlife
habitat is normal and acceptable.
Mountain bikers like to claim that excluding them from trails
constitutes "discrimination". They say that other user groups (hikers
and equestrians) receive better treatment from land managers. There is
no basis for such a claim, since all users are subject to exactly the
same rules. For example, on a trail closed to bikes, everyone is
allowed on the trail -- only the bikes are excluded! In spite of what
they claim, mountain bikers have never been excluded from any trail!
Even if my way of "enjoying" the wilderness is to race my bulldozer
there, I am not allowed to do that. And this is not because land
managers like hikers more than bulldozer racers. I am not being
excluded from the wilderness; I can go there whenever I want, as long
as I don't try to bring my bulldozer with me. It is only the bulldozer
that is excluded, which is due to its effects on wildlife and people.
If mountain bikers were actually being discriminated against,
they could sue park managers for access to every trail that others are
allowed on. On the contrary, the U. S. Court of Appeals for the Ninth
Circuit (Bicycle Trails Council v. Bruce Babbitt) concluded that the
National Park Service has the right to ban bikes from trails. "All
units of the National Parks [are] to be treated consistently, with
resource protection the primary goal". "All bicycle use of off-road
areas [is] prohibited unless local park superintendents [designate]
particular trails to be open" (bicyclists were contesting this rule).
"Routes may only be designated for bicycle use based on a written
determination that such use is consistent with the protection of the
park area's natural, scenic and aesthetic values, safety
considerations and management objectives and will not disturb wildlife
or park resources". "The Park Service is empowered with the authority
to determine what uses of park resources are proper and what
proportion of the park's resources are available for each use". "The
use of bicycles is allowed in park areas under the same basic
conditions as are motor vehicles, i.e. on park roads, in parking
areas, and on routes designated for their use. ... certain limitations
on their use are necessary and appropriate in the interest of public
safety, resource protection, and the avoidance of visitor conflict"
Clearly, bikes are not being banned from trails because land
managers like hikers and equestrians more! As people, mountain bikers
are indistinguishable from other park users. It is the bikes that we
object to, and not even the bikes, but their presence in natural
areas. Banning bikes is simply a humane way of protecting our natural
areas, while allowing all users equal access to enjoy them. Thus,
whether bikers or hikers or equestrians are more harmful to wildlife
(they all are, of course) is irrelevant. Restricting bicycle access is
a way of reducing human impacts on wildlife and wildlife habitat.
The Case of Brown's Woods
Brown's Woods, one of the last stands of native forest in
central Iowa (southwest of DesMoines), illustrates these issues. It
was saved from logging and development in 1972 by the S. E. Polk (High
School) Ecology Club and their sponsor, biology teacher, Kirk Brill,
for which they won a national award. Motorized vehicles were banned,
"because of the threat they posed to the environment and to persons
walking there" (Wayne Bills, Polk County Conservation Board (PCCB)
Executive Director, 1972). The students worked hard to earn money to
build two miles of bike trails through the preserve.
However mountain bikers illegally built 4 1/2 additional miles
of trail ("bikers have gouged more than six miles of trail, up to 30
feet wide and a foot or more deep in spots" (Loren Lown, PCCB Natural
Resources Specialist, 1996)). Wildlife were disappearing, elderly
hikers were driven out, and vegetation was destroyed. "Already the
bikers have caused permanent irreparable damage to this pristine area"
(Ben Van Gundy, PCCB Director). It was called "ecological vandalism".
Last year, once again, Brill and his students were forced to campaign
to save the preserve, this time from mountain bikers, and won, getting
a unanimous vote of the PCCB for a "total and permanent ban on the use
of mountain bikes" in Brown's Woods.
Millions of mountain bikes are being sold every year around
the world. Let's not wait till "bikers have caused permanent
irreparable damage" to our other natural areas! We can't eliminate all
environmental damage, but we can eliminate frivolous, unnecessary
damage. True civilization is characterized by restraint.
"It is expected that outdoor recreational activity will
continue to increase, while the amount of wild land where wildlife may
seek refuge from disturbance will decrease" (Knight and Gutzwiller,
p.327); "Recreationists are, ironically, destroying the very thing
they love: the blooming buzzing confusion of nature.... The recreation
industry deserves to be listed on the same page with interests that
are cutting the last of the old-growth forests, washing fertile
topsoils into the sea, and pouring billions of tons of greenhouse
gases into the atmosphere" (p.340; emphasis added); "Tom Birch ...
argues that wilderness managers, charged with incarcerating
wilderness, are more concerned with the advancement of their careers
through achieving quantifiable goals (number of park visitors, total
revenues) and developing park and forest amenities (roads, 'scenic'
turnouts, restrooms, paved trails, maps, campgrounds) than with
perpetuating the land community of which they are a part" (p.344).
Ideally, we should be working to reduce all human access to
wildlife habitat. But at the very least, we should eliminate
mechanical access (with the exception of small compromises for
Bicycle Trails Council of Marin v. Bruce Babbitt, No.C-93-0009,slip
op. (N. Dist. Cal., Sept. 1, 1994) (see also Third Circuit Case
Ehrlich, Paul and Anne, Extinction: The Causes and Consequences of the
Disappearance of Species. c.1981.
Knight, Richard L. and Kevin J. Gutzwiller, eds. Wildlife and
Recreationists. Covelo, California: Island Press, c.1995.
Liddle, Michael, Recreation Ecology. Chapman & Hall: London, c.1997.
Phillips, Kathryn, Tracking the Vanishing Frogs: An Ecological
Mystery. New York: St. Martin's Press, 1994.
Stebbins, Robert, personal communication.
Vandeman, Michael J., Ph.D.
I am working on creating wildlife habitat that is off-limits to
humans ("pure habitat"). Want to help? (I spent the previous 8
years fighting auto dependence and road construction.)
Please don't put a cell phone next to any part of your body that you are fond of!