May 17, 2001

Board of Directors

Sierra Club

85 Second Street

San Francisco, CA 94105-5799


Re: The Sierra Club's Mountain (Off-Road) Biking Policy




     You will soon be presented with the following resolution passed by the San Francisco Bay Chapter (SFBC) on Monday, May 14, 2001: "The San Francisco Bay Chapter urges the Board of Directors to initiate a review of the Park City Accord in order to determine whether it should be modified or rescinded." While it sounds equivocal, that was only due to the usual compromises undertaken to get it passed as easily as possible. Obviously, it was passed because the majority agrees that something in the Park City Agreement, and the policy on mountain biking that it gave rise to, has to change!


     Here is the original resolution passed by the Wildlife Committee of the SFBC:


"Wildlife Committee Resolution




1. Mountain bikes greatly increase erosion, particularly, creating narrow ruts that make walking difficult, widening trails, removing top soil and vegetation, and making trail treads slippery and dangerous; this is due to their knobby tires, additional weight, and increased speed, momentum, acceleration, and skidding;


2. They make it much easier for people to get farther into wildlife habitat and travel farther in the same length of time, thus posing an increased threat to wildlife;


3. The speed at which they travel makes it more difficult to notice small animals and plants in the trail and avoid crushing them;


4. Bikes, especially on the narrow trails that mountain bikers prefer, and at the speeds that many mountain bikers travel, intimidate, displace, and endanger wildlife and people;


5. Mountain biking is bad role modelling, because children who see people on mountain bikes learn (non-verbally) that rough treatment of natural areas is okay;


6. The Park City Agreement with IMBA (International Mountain Biking Association) was to gain support for Wilderness designation from mountain bikers; however, IMBA and mountain bikers have been opposing Wilderness designation because Wilderness by definition is off-limits to machinery such as bikes. They have instead been lobbying for "protected" areas to be administered under designations that allow mountain biking. They are also asking for new wilderness areas to be "gerrymandered" to exclude trails that they want to remain open to mountain biking. In addition, the process by which the Park City Agreement and mountain bike policy were created was undemocratic and thus violated Club policy: input from Club members opposing the changes was ignored, and some were even excluded from meetings where deliberations were conducted!


7. Its support of mountain biking is an embarrassment for the Club, since it is so obviously an anti-environmental activity, akin to the use of motorized ORVs.


8. The presence of mountain bikes negatively impacts one's experience of tranquil nature, because they remind us of the urban environment and its associated stresses -- exactly what we are trying to escape from!


Therefore be it resolved that:


The Sierra Club actively oppose the off-road use of bicycles, mountain boards, and all other off-road vehicles;


The Club eliminate its separate mountain biking policy, and subsume mountain biking under the ORV policy, as it was before the Park City Agreement -- in other words, rescind that agreement."


Passed by the Northern Alameda County Group:


"The Northern Alameda County Group asks the Sierra Club Board of Directors that:


The Sierra Club actively oppose the use of bicycles on single-track trails;


The Club eliminate its separate mountain biking policy, and subsume mountain biking under the ORV policy, as it was before the Park City Agreement -- in other words, rescind that agreement."


Later passed by the Northern Alameda County Group:


"The Northern Alameda County Group asks the Sierra Club Board of Directors to replace the existing 'Off-Road Use of Bicycles' Policy with the following: we oppose all use of bicycles off of pavement, except for essential transportation in lieu of motor vehicle use."


     The ideal policy on mountain biking -- one that allows bicyclists to enjoy their sport, while protecting wildlife and wildlife habitat -- is that of Yosemite National Park: bicycles are restricted to pavement. It is highly unusual that a land manager would implement a policy more protective of wildlife than the Sierra Club's policy, but there it is! ("Bicycles (including mountain bikes), in-line skates, scooters, and strollers must remain on paved roads and designated paved bike paths. They are not allowed on hiking trails or anywhere off-pavement." See


     Here are some of the reasons why the Club should rescind the Park City Accord and the mountain biking policy it produced, and adopt the Yosemite rule:


     For about four million years prior to 1980, human beings felt themselves capable of enjoying nature without bringing along large pieces of machinery. With the advent of the mountain bike, many people now seem incapable of enjoying nature except from the top of a mountain bike: they claim that banning bikes "excludes" them from the area. We are literally creating a generation that is too lazy to walk, and a generation that thinks that the rough treatment of natural areas is an acceptable activity! It is also impossible to pay much attention to nature, while having to control a bicycle, often on unfamiliar trails, at the same time: we are creating a generation that sees nature purely as a human playground, whose purpose is to provide "technical singletrack" and other physical challenges.


     Since ordinary bicycles can't take the pounding that they would receive off of pavement, special "mountain" bikes had to be built that could withstand such punishment. By Newton's laws of physics, the pounding that the bike receives is identical to the pounding that it applies to the trail! According to recent statistics from the Sporting Goods Manufacturers Association, there are approximately 8 million mountain bikers. That is an enormous beating that we are giving our precious, scanty remaining wildlife habitat! One look at a mountain bike is enough to tell you that it is up to no good: the knobby tires are designed to rip up the soil, and the suspension systems are designed to insulate the rider from the shocks, as they beat the trail to a pulp.


     While hikers generally step over tree roots, and cross streams by means of stepping stones, logs, or bridges, bikers usually ride across the tree roots, ripping off the bark, and ride through the stream bed, destroying that habitat (see e.g. and Most hikers use shoes with flat soles, leaving the trail practically as they found it. Bikes, on the other hand, tend to create narrow V-shaped grooves that are not only difficult or impossible to walk on, but also difficult to bike on! Therefore, everyone is forced to continually widen the trail. Thus, allowing bikes on trails greatly increases the need for, and the cost of, trail maintenance, subjecting wildlife to further human intrusion. Knobby tires are also designed to rip up the soil, accelerating erosion. Bikes increase the total weight of the trail user, as well as the pressure (weight per unit area) on the soil: the "footprint" of a bike is much smaller than that of a hiker. Bikers also travel several times as fast as a hiker (increasing the horizontal forces on the soil), and several times as far (multiplying their impacts on wildlife and wildlife habitat).


     Several "studies" have been produced that claim to show equal impacts from hikers and bikers. However, even if we accept that dubious result, what they actually measure is impacts per mile! Thus, the biker's total impact is still several times that of a hiker, because they travel so much farther. I have monitored mountain bikers' newsgroups and email lists for several years. They consistently advertise their rides as being between 17 and 60 miles per day. My typical hike is a few miles. I once hiked 15 miles (while investigating mountain bike damage at Pleasanton Ridge Regional Park), but at the end, I could barely walk!


     In 1994, REI (which makes millions of dollars from selling mountain bikes) sponsored a "back room" meeting between the International Mountain Biking Association (IMBA) and some mountain bikers from the Sierra Club. They created the Park City Agreement and Sierra Club's Off-Road Bicycling Policy in a process that was highly undemocratic. Most opponents of mountain biking were told that they couldn't even be present at the meetings! ("While large, active segments of long-standing Sierra Club members were excluded from this process, in particular the hiking community, an outside organization was invited in as a 'partner'. … We find it unseemly for an outside organization to have such influence on Sierra Club policy." Bay Area Trails Preservation Council) We were allowed to write comments on the proposed policy, but most of our comments were ignored. All of mine were ignored. Of course, the mountain bikers knew that if the process were democratic, it never would have passed! Then when the Policy went before the Board of Directors, they told the Board (according to Paul Wilson, chair of the Wild Planet Strategy Committee) that "there was no opposition"! At the time, I couldn't understand why the Board would fall for such a blatantly anti-environmental proposal. Now I understand! They were lied to!


     In creating the mountain biking policy, they started with a copy of the ORV policy, which is excellent. But then they began weakening it, even throwing out important clauses (e.g. "Soil compaction and serious adverse impact on flora and its regeneration" and "Disruption of wildlife breeding and nesting habitats, especially of vulnerable species, resulting in loss of young; disturbance of wildlife, leading to weakened physical condition, death, and possible extinction of some species"), as if assuming that mountain bikers have no impact on wildlife!


     To understand how the off-road biking policy came about, and why it is so weak, it helps to realize that in 1994, the effects of the presence of humans on wildlife was hardly studied and not well known. Richard Knight and Kevin Gutzwiller's summary of research, Wildlife and Recreationists, was published in 1995. Michael Liddle's Recreation Ecology was published in 1997. The Montana Chapter of the Wildlife Society's "Effects of Recreation on Rocky Mountain Wildlife" came out in 1999. (The mountain bikers like to complain that bikes have been banned without scientific justification. However, no science whatsoever was cited in the Park City Accord to back up the claim that "mountain bicycling is a legitimate form of recreation and transportation on trails, including single track".) Thus, the policy takes the view that the only important effects on wildlife are "measurable", direct impacts, such as erosion. Its primary concern is with the effects on other trail users.


     In the long run, probably the greatest harm that mountain biking will do is to vastly increase the human "footprint" in wildlife habitat. Since bikes have been allowed on trails, the number of people invading wildlife habitat, the area that they have impacted, the amount of time that they spend there, as well as the extent of physical damage, has increased enormously. In some parks, such as China Camp State Park and Pleasanton Ridge Regional Park in the San Francisco Bay Area, mountain bikers now far outnumber hikers. Many mountain bikers have even started biking at night, partly to be able to bike illegally and not get caught. All of this effectively shrinks the habitat available to wildlife.    It is now possible to visit those parks and see almost no wild animals!


     None of this is considered in the off-road bike policy. It assumes that there is such a thing as "responsible" mountain biking, and that it is benign. In fact, all mountain biking, however politely it is practiced, accelerates erosion, kills wildlife, drives animals out of their preferred habitat, and drives other trail users out of the parks. Multi-use trails inevitable become mountain-bike-only trails. (We visit the parks for their naturalness and tranquility, and don't want to be around large pieces of machinery -- of which we all get our fill in the city.) From the point of view of wildlife, all mountain biking is irresponsible (and all hiking, for that matter, but that is a topic for another discussion).


     Some people claim that mountain biking is harmful on narrow hiking trails, but okay on wide trails. The laws of physics are the same everywhere! Bikes have the same effect on unpaved roads that they have on trails. In fact, the effects are greater, because roads allow for greater speed. And wildlife, of course, are affected the same, whether on a road or a trail. Even hikers and equestrians are not made safe by widening the trail. The "Majority Report" (from the Mountain Bike Access Working Group, Los Angeles -- sent under separate cover) describes numerous dangerous and sometimes fatal encounters between mountain bikers and equestrians on wide trails. Allowing bikes on wide trails gives parks a loophole that allows them to simply make all trails wide, destroying even more habitat and destroying the natural feel of the park! Hiking trails are for the peaceful contemplation of nature -- something that is impossible when bikes are present.


     Mountain biking makes parks very expensive to maintain and police, drawing resources away from wildlife protection. The only way for police to catch renegade mountain bikers is with a motorcycle, which is expensive and further harms the park. There is no practical way to enforce rules that allow bikes on only some trails. In addition, bikes carry seeds and spores on their tires, propagating exotic species long distances. For example, they are suspected of being a major factor in the transmission of Sudden Oak Death in the San Francisco Bay Area, California. Mountain bikers also "use up" parks more quickly: they transit trails so fast that they soon get bored with them, and start clamoring for more trails to be open to bikes. It also means that they soon need to drive long distances to find suitable places to ride. Hikers, who experience every sight, sound, touch, smell, and sometimes taste as they walk, may never exhaust the delights of nearby trails. I have hiked some of the same trails for eighteen years, without ever getting bored with them!


     Mountain bikers also claim that it is only a "small minority" of bikers that are the problem. As I pointed out, all mountain bikers accelerate erosion and invade wildlife habitat. And a study published on IMBA's own web site ( found that it is actually not a minority, but a large majority of mountain bikers who violate the rules!


     In the Park City Agreement (PCA), IMBA agreed to "to work for Wilderness". In the seven years since the PCA was concluded, IMBA has actually done just the opposite! Rather than supporting Wilderness and Wilderness proposals, they consistently ask (1) that areas where they want to mountain bike be excised from the Wilderness proposals, making them smaller than they should be, or (2) that the area be designated something other than "Wilderness", so that they can mountain bike there. They state this clearly on their web site ( "IMBA is committed to maintaining access to traditional and important bicycle trails through attention to Wilderness boundaries and the use of alternative land protection designations (e.g., National Conservation Areas, Wild and Scenic River Zones, Areas of Critical Environmental Concern, National Monuments, etc.)." But what do we expect? Their charter, dictated by their 30,000 members, is to promote mountain biking!


     This and many other pieces of evidence (some of which I attach) demonstrate that the Park City Agreement has benefited the mountain bikers enormously (they often use it to claim that the Sierra Club supports mountain biking), but has not benefited the Club at all. For example, of the dozens of groups included in the California Wild Heritage (Wilderness) Campaign, not one is a mountain biking organization. Some people have claimed that the Park City Agreement has benefited the Sierra Club. However, they haven't been able to produce one shred of evidence that this is true. How long do we have to wait, for these alleged benefits to show themselves?


     The mountain bikers like to say that this is just a problem of inadequate education of riders and other trail users. But how long do we have to wait, for this "education" to take effect? We have already waited for twenty years, and the problem seems, if anything, to be getting worse! The same goes for improving enforcement. It isn't happening, the necessary funds aren't available, and, besides, they are needed for more important priorities.


     In the seven years that I have been talking about the harm that mountain biking does to the environment, I have received every conceivable kind of harassment. My house has been vandalized four times, I get frequent harassing phone calls, I have been physically attacked five times on trails closed to bikes, and I have received numerous threats, including several death threats. If mountain biking is truly a "legitimate form of recreation", as they claim, why do mountain bikers need to resort to such Gestapo tactics???


     It's time to jettison the Park City Agreement, which after 7 years is still a complete failure, and replace our wimpy, equivocal off-road biking policy with one that actually furthers the conservation and recreation goals of the Sierra Club. It is an embarrassment for the Club to be associated with an organization like IMBA, whose members have been involved in so many illegal activities harmful to wildlife and the environment. It may make mountain bikers happy, but it has been driving away many people who truly care about wildlife, who are disgusted with the Club's hypocrisy, as demonstrated in its love affair with mountain biking. The Sierra Club should no more endorse mountain biking than it does any other extreme sport.


                             Sincerely yours,


                             Michael J. Vandeman, Ph.D.


Cc: Paul Wilson, Wild Planet Strategy Committee


"[We] can afford to sacrifice almost any other value for the sake of retaining something of the primitive…. To countless people the wilderness provides the ultimate delight because it combines the thrills of jeopardy and beauty. It is the last stand for that glorious adventure into the physically unknown that was commonplace in the lives of our ancestors and has always constituted a major factor in the happiness of many exploratory souls. It is also the perfect esthetic experience because it appeals to all of the senses…. It is all of these at the same time, blended into a unity that can only be appreciated with leisure and which is ruined by artificiality…. Quality as well as quantity must enter into any evaluation of competing types of recreation, because one really deep experience may be worth an infinite number of ordinary experiences. Therefore, it is preposterous to hold that the objective of outdoor recreational planning should be to enable the maximum number of people to enjoy every beautiful bit of the outdoors. All the while year after year, the Unites States becomes more and more mechanized. The life of one person after another has been saturated by machinery. Humans beings require compensations and it seems inevitable that as the machine age expands the need for an escape will also expand." Robert Marshall, "The Universe of the Wilderness Is Vanishing", Nature Magazine, April, 1937 [emphasis added].




Ehrlich, Paul R. and Ehrlich, Anne H., Extinction: The Causes and Consequences of the Disappearances of Species. New York: Random House, 1981.


Foreman, Dave, Confessions of an Eco-Warrior. New York: Harmony Books, 1991.


Grumbine, R. Edward, Ghost Bears. Washington, DC: Island Press, 1992.


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.


Life on the Edge. A Guide to California's Endangered Natural Resources: Wildlife. Santa Cruz, California: BioSystem Books, 1994.


The Montana Chapter of the Wildlife Society (, "Effects of Recreation on Rocky Mountain Wildlife", 1999.


Mountain Bike Access Working Group (A Citizens Advisory Body Convened by the City of Los Angeles Department of Parks and Recreation), "Majority Report", September 15, 2000.


Myers, Norman, ed., Gaia: An Atlas of Planet Management, Garden City, NY: Anchor Books, 1984.


Noss, Reed F., "The Ecological Effects of Roads", in "Killing Roads", Earth First!


Noss, Reed F. and Allen Y. Cooperrider, Saving Nature's Legacy: Protecting and Restoring Biodiversity. Island Press, Covelo, California, 1994.


Stone, Christopher D., Should Trees Have Standing? Toward Legal Rights for Natural Objects. Los Altos, California: William Kaufmann, Inc., 1973.


Vandeman, Michael J., and, especially "The Effects of Mountain Biking on Wildlife and People" and "There Is No Right To Mountain Bike: Bicycle Trails Council of Marin v. Babbitt, 82 F.3d 1445, 1452 (9th Cir. 1996) (


Ward, Peter Douglas, The End of Evolution: On Mass Extinctions and the Preservation of Biodiversity. New York: Bantam Books, 1994.


"The Wildlands Project", Wild Earth. Richmond, Vermont: The Cenozoic Society, 1994.


Wilson, Edward O., The Diversity of Life. Cambridge, Massachusetts: Harvard University Press, 1992.