Proposed Sierra Club Resolution

Michael Vandeman, Ph.D.

May 30, 2021

Updated August 6, 2021


  1. There is no good reason to allow bicycles on any unpaved trail. For example, bicycles provide exercise, but so does walking, and it’s much safer – no broken bones, paralysis, or deaths.  Bicycles allow you to experience nature, but so does walking, and much more effectively: while bicycling, you have to keep your eyes on the trail, or you will crash; while walking, you are free to look around as much as you like: "Something I didn't know about mountain biking, at least on a trail this challenging: You cannot look up. Even for a second. To do so is to court ruin. Forget about the scenery, all that peripheral beauty gone by in a flash, the profound silence, the bliss of seclusion. Was that a bull elk up ahead or merely a juniper? Oh, how the rings of morning light smolder over that ridgeline ... Wake up! Dial it in, man! Head down! Eyes locked on the trail! Let your mind drift and you are toast."


  1. Mountain bikes generate erosion. Knobby tires are perfectly designed to dig up the soil and grind it to dust. Soil that is lost due to wind or rain is lost forever. They also create V-shaped grooves that make walking difficult or even dangerous. The grooves channel rainwater, accelerating the erosion and eventually making the rut impassible. Mountain bikers themselves use the expression "shred trails" for mountain biking. That is not an accident. That is exactly what knobby tires are designed to do!


  1. Bicycles kill small animals and plants on and next to the trail. Mountain bikers travel much faster and farther than hikers, and thus are far more likely to kill animals and plants. A perfect example is the Alameda whipsnake – a federally Threatened species – killed in Black Diamond Mines Regional Park by a mountain biker. Whipsnakes are very fast, and very unlikely to be killed by a hiker.


  1. Bicycles greatly increase the human footprint (the speed and distance travelled) in our parks, thus greatly increasing the impact on the wildlife, as well as other trail users. For example, a mountain bike ride announcement listed the distance as 115 miles. No one is going to hike anywhere close to 115 miles in a day!


  1. Bicycles are a danger to other trail users. Good trails (that are narrow, so as to minimize habitat destruction) are not designed to accommodate bicycles, forcing hikers and equestrians to be ready to leap off the trail at any moment to avoid getting hit. That destroys the value of the peaceful experience of nature that the vast majority of trail users (hikers and equestrians) are seeking. (Mountain bikers, who are seeking much greater stimulation, probably don’t understand that. They think that hikers are just being selfish in not wanting to share the trails with them. But that is nonsense. Hikers have no problem sharing trails with mountain bikers. It’s only the bikes that are the problem.) Mountain biking is driving the very young and old off of the trails and hence out of the parks. Even able-bodied hikers and equestrians fear for their safety, and don’t enjoy sharing the trails with large, fast-moving pieces of machinery, such as bikes. Strava ( is a web site that mountain bikers use to compete with each other to see who can ride trails (some legal, some illegal) the fastest, thus turning every trail into a racetrack, further endangering all trail users. Equestrians and hikers theoretically have the right-of-way on all trails, but try to claim your right-of-way when a mountain biker is racing to claim the fastest time on that trail, and resents anything that slows him down!


  1. Banning bicycles from unpaved trails is not discriminatory. The same rules apply to everyone, so where is the discrimination? This was verified in 1996 in federal court, where the judge said that land managers are allowed to ban bicycles. If that were discriminatory, it would not be allowed (see Banning bicycles doesn’t in any way prevent mountain bikers from visiting the park and hiking its trails. Every mountain biker is capable of walking; if they weren’t, a simple flat tire would strand them in the wilderness. But because mountain bikers falsely believe that they are being discriminated against, they have embraced an “entitlement mentality” to justify illegal riding and illegal trail-building. In fact, permitting bikes on trails is discriminatory, because it drives other trail users off the trails and hence out of the parks (which they own!).


  1. Banning bicycles from unpaved trails would eliminate the vast majority of user conflicts. After more than 30 years, conflicts between mountain bikers and other trail users have never gone away. If there were another solution to this problem, it would have been tried and would have succeeded long ago!


  1. There is no other way to eliminate these conflicts. Alternate day use is unfair to the majority of park users (hikers and equestrians). Building separate trails just for mountain bikers would destroy an enormous amount of habitat, and thus be unfair to the wildlife. Widening trails (as the East Bay Regional Park District seems to want to do) would do the same: destroy an enormous amount of habitat, and for no good reason.


  1. A hiker, when crossing a creek, will try to avoid getting wet, by crossing on stepping stones or logs. Mountain bikers, on the other hand, simply ride right through the creek bed, crushing any animals or plants that happen to be there. Mountain biking magazines are full of photos of mountain bikers throwing up spray, as they barrel through creeks. Not only do bikes destroy animals and plants as they ride across streams, they ride through streams stirring up sediment. The sediment in the water interferes with the oxygen uptake by aquatic life, for example, killing fish- and frog eggs. Young fish, insects, amphibians, and aquatic microorganisms are extremely sensitive to sediment in water.


  1. Knobby mountain bike tires are ideal for carrying mud, and consequently exotic plants, fungi, and other organisms from place to place, resulting in the spread of exotic invasive species, such as weeds and Sudden Oak Death.


  1. Mountain bikes, which are obviously built to go anywhere, teach children and anyone else who sees them that the rough treatment (abuse) of nature is acceptable. This undoubtedly has a negative effect on people's treatment of nature.



  1. In order to mitigate bike-caused erosion, park managers have been resorting to extreme measures -- even in some cases putting a plastic matrix or other exotic material under the trail (e.g. in Pleasanton Ridge Regional Preserve, near Pleasanton, California and Crockett Hills Regional Park near Martinez, California)! It's hard to imagine that this will have a beneficial effect on the park and its wildlife….


  1. Allowing mountain bikes in a park greatly increases the damage to the trails, damage from "bootleg" (illegally created) trails, and the problems of conflicts between trail users, and hence the cost of maintaining the park. Considering how tight park budgets always are, we can't afford the extra costs of policing, and repairing the damage from, mountain biking.


  1. For the science on mountain biking and its impacts on wildlife and people, see


  1. Mountain bikers ride so fast that they don't experience most of what they are passing, and quickly get bored with any given trail, and then want more and more trails to ride. If they can't get enough trails to ride legally, they ride illegally. Or they build new trails. If they can't get legal permission to build them, they build them illegally. They are insatiable! See regarding the habitat destruction caused by trail-building. "Kyle Legge, who will go to Orange Coast College in the fall, enjoys carving through canyon trails.' You kind of forget about everything else,' he said. 'You’re just focusing on the trail and what’s in front of you.'" "'Mountain biking is different than [sic] road biking. It takes a lot of focus to be on the trial [sic],' 16-year-old Jacob Venenga said. 'Dr. Schindler taught me how to keep that focus. Focus on what is ahead, not what’s around.'" Trail building, of course, destroys wildlife habitat, not only underfoot, but also a wide swath on both sides of the trail, since the presence of humans prevents the animals from using the area (see Here is IMBA (International Mountain Bicycling Association) bragging about all the trail building they do, which is actually nothing to be proud of!:

From: "IMBA" <>
Subject: Get incredible mountain biking, right near your place
Date: Thu, 14 Aug 2014 06:45:18 -0600

Heres [sic] the deal...

1. Mountain biking is awesome.

2. Building and maintaining trails is expensive.

3. If we wait for someone else to fund great riding, trails wont [sic] get built, and we wont [sic] ride.

Last year, IMBA's professional trailbuilders built 13 bike parks and 450 miles of new trails. Check the map to see what's happening near you.

And we helped volunteers build and maintain thousands more through grants and technical assistance.

This year, were ready to do it all again, but we need your support.

It's vital that you and every mountain biker pitches in.

Whether its $20, $50, $250 please give what you can to the Trail Building Fund.

Donating is the most effective way to fund trails; the money is matched by other supporters and goes back out to enable local trail work across the U.S.

As a thank you, IMBA will send you a gift of your choice like a limited-edition IMBA cap or a Tech T-shirt only available when you donate now.

Build It. Ride It. Support It.

Thank you!

Michael Van Abel, Executive Director

P.S. Donations to IMBA are tax-deductible and earn 20 percent off anything at the IMBA store. Click here now for your discount code.

207 Canyon BLVD
Suite 301
Boulder, CO 80302
United States

IMBA 5/31/18: "Most hometown trails are built and cared for by local mountain bike groups in support of under-resourced land managers." In other words, habitat destruction is a big part of mountain bikers' mission! This shows exactly why mountain bikers should never be allowed to build trails! Where a hiker only needs a relatively straight trail from point A to point B, mountain bikers want extra twists and bumps to give them thrills, making the trail much longer than necessary and destroying far more habitat.


16. Mountain bikers claim that their sport has no greater environmental impact than hiking. Is that true?

a. If you read the "studies" that make that claim, you find that they don't really compare the impacts of hiking and mountain biking, but only the impacts per foot. If, for a moment, we assume that the studies are correct in their having equivalent impacts per foot, it would still follow that mountain biking has far greater impact per person, since mountain bikers typically travel so much farther than hikers. Besides overlooking distances travelled, those "studies" almost all ignore impacts on wildlife. And they don't study mountain biking under normal conditions -- only at a very slow speed. Actually, the comparison with hiking is irrelevant. It would only be relevant if we planned to allow only one of the two, and were considering which of the two is more harmful. In fact, no one is considering banning hiking. We are only considering adding mountain biking. Therefore, the only relevant question is, "Is mountain biking harmful"? (Of course, it is!) There is only one truly scientific study that I know of that compares the impacts of hiking and mountain biking. It found that mountain biking has a greater impact on elk than hiking (Wisdom, M. J., H. K. Preisler, N. J. Cimon, B. K. Johnson. 2004. Effects of Off-Road Recreation on Mule Deer and Elk. Transactions of the North American Wildlife and Natural Resource Conference 69, 2004, pp.531-550.) See

     b. On its web site, IMBA mentions recent research on mountain biking by Dave White et al and Jeff Marion, both of whom claim that mountain biking and hiking have "similar" impacts. Is that true? First, "similar" is not a scientific term and really has no clear meaning. That term is being used only to obfuscate. Second, these are survey studies, not experimental studies. By its very nature, a survey study cannot be used to compare the impacts from two activities, because it doesn't control all the variables. For example, we don't know if the differences in erosion between two trails are due to the mountain biking vs. hiking use, or due to differences in the weather, terrain, steepness, soil type, management practices, amount of use, hikers on the "mountain biking trail", mountain bikers on the "hiking trail", etc. White et al only measured their trails once, and didn't even collect any data on hiking impacts! See and

     c. Why would a researcher risk his/her reputation by doing such shoddy work? For money! And to ensure the continuance of their sport. If land managers think that mountain biking is more harmful than hiking, they will be more likely to close trails to bikes. Bike parts manufacturer Shimano paid Professor White to do his study. Research funds are difficult to obtain. A researcher who can be relied upon to produce research favorable to mountain biking will be able to obtain funding from the mountain biking industry. A researcher who tells the truth about mountain biking won't be able to obtain research funds and will risk stunting his/her career.


17. Where should mountain biking allowed? A couple of role models for wildlife protection are Yosemite National Park and East Bay Municipal Utility District (in Alameda and Contra Costa counties, California). They both restrict bicycles to paved roads, where they can't do much harm. Somehow bicyclists have managed to enjoy their sport for over a hundred years, without riding off-road. As far as I know, there are only four national parks that permit mountain biking: Cuyahoga, Big Bend, Redwood, and Saguaro. Obvously, the National Park Service understands the harm that mountain biking does.


18. What should the policy be on trails? Closed to bikes, unless marked open. Signs that say "No Bikes" are quickly and repeatedly ripped out of the ground by mountain bikers. Bikes should never be permitted on any unpaved trail.


19. Overview of common mountain bike injuries:


20. Isn't mountain biking good for kids, since it gets them off the couch? Mountain bikers would like you to believe that mountain biking is the only thing that will get kids off the couch (there are many less harmful physical activities that will do that, including hiking and street bicycling), and that mountain bike racing is environmentally benign and is beneficial for the kids (at least the ones that aren't seriously injured or killed!). The psychology of racing (e.g. Peak Mental Performance Coaching: is all about ignoring everything and everyone in the world, so that you can win a race. I have never had any interest in racing, so I can't say whether it works, but it does seem to embody everything that is bad about mountain biking: ignoring erosion, the killing of animals and plants, the terrorizing of other trail users, and the endangerment of mountain bikers and others. This is why it is so important to "nip it in the bud" - in grade school and high school, where the racing addiction is fostered - by people who care more about spreading their sport than they do about the welfare of children.


21. Isn't it good to get more people on bikes, and thereby clean up the air? It's good to get people out of their cars and riding bikes instead. But mountain biking doesn't do that – it is done for recreation, not transportation, and doesn't replace motor vehicle trips. In fact, most mountain bikers drive to the trailhead, since very few mountain biking trails are within bicycling distance of their homes. And mountain biking dirties the air: one day I met a woman who told me that a mountain biker (on a trail closed to bikes) skidded past her at high speed and filled the air – and her lungs – with dust!


22. One more reason to ban mountain biking: the enormous cost of rescuing someone from the wilds, often with helicopters or all-terrain vehicles, and medical personnel.


23. The speed limit for bicycles in the East Bay Regional Park District is 15 MPH. But the only way to enforce that rule is for the police to ride dirt bikes, which are even more destructive than mountain bikes!


24. Mountain biking is extremely dangerous: Broken bones, paralysis, and even deaths are common. Mountain bikers claim that mountain biking provides a financial boost to the community, but that ignores the cost of these injuries and the increased load on emergency services, such as search and rescue.


25. Mountain biking is addicting, which many mountain bikers have admitted. You can tell by the fact that mountain bikers continue mountain biking even when it hurts them or their family or friends. Even mountain bikers who turn themselves into paraplegics or quadriplegics still seek ways to continue their sport! That is the sign of an addiction. See


26. What is the point of mountain biking? Mountain biking through the wilderness is like bicycling through an art museum. How much are you going to see? Is that a good way to learn about art?


27. The Sierra Club is supposed to be a democratic organization. All policies are supposed to start at the chapter level and work their way up through all levels to the Board of Directors. But the Club’s mountain biking policy was created through an anti-democratic process. REI hosted a meeting with IMBA (International Mountain Bicycling Association) and the Sierra Club at Park City, Utah in 1994. Anyone opposed to mountain biking, such as me, were excluded from the meeting! The Sierra Club agreed to support mountain biking where it isn’t harmful to the environment (which doesn’t exist), and IMBA agreed to support Wilderness designation. But IMBA has never lived up to its side of the bargain! It has never supported Wilderness designation. The Club was hoodwinked. The Club’s policy should be rescinded. It was illegitimate from the start.


Be it resolved that bicycles and other non-emergency vehicles should not be allowed on any unpaved trails.


P.S. If you disagree, please explain why. Also, if I missed any important issues, please let me know.