Environmental Impacts of Mountain Biking Synopsis
By Jason Kahn
Featured Image: An mountain biking xc trail in Hampshire County, MA. (c) Jason Kahn
According to the online mountain bike trail database, Trailforks, there are currently 283,020 miles of 213,921 trails in 109 countries. This list mostly includes approved trails on public and private lands. The numbers in this database almost certainly under-estimate the actual number of trails and trail mileage. It may be assumed that rogue or pirate trails may double the existing number of trails currently documented.
There are four types of mountain bike riding and therefore four types of trails. Each has unique characteristics and environmental impacts. These types of riding are: Cross Country(XC), Freeride, Down Hill(DH) & Bike Park/ Pump Track.
Cross Country trails are traditionally narrow, 12” to 24” in width, and meandering; the idea being that the trail is the goal. As such the trail density may be quite high. For example, 4 miles of trail can easily be constructed in 0.0078 square miles if desired. The other end of the XC spectrum may have 1.5 miles of trail spread over 1 square mile. The trail density is usually dependent on the size of the area available to the trail builder. The trails tend to cross slopes with no more than a 5-8% slope so as to be ridden in both directions for maximum variety. Trail building best practices, according to International Mountain Bike Association (IMBA) standards, allow for water to flow across trails instead of down the trail. Where trails reverse direction (switchbacks), they tend to have water bars built into the trail before and after the switchback. This prohibits water pooling which creates muddy conditions and erodes the trail tread. XC style mountain bike trails have similar erosional impacts to hiking trails. In fact, some studies have found the erosion due to hiking trails more detrimental due to bad practices. Horse packing/equestrian trails are considered the most damaging.
Freeride trails are a combination of XC and DH trail-building and riding. They are wider than XC trails, 3’ to 6’. They are meant to be ridden in one direction, down, and are therefore more susceptible to erosion due to speed, braking, and landscape features such as slope. Erosion may be limited by armoring the trail, placing rocks in the trail tread in areas that tend to be wet, or building bridges over these areas. Most of these types of trails are on private land such as ski resorts that are trying to build a year-round tourist base. Another feature of Freeride trails is berms, these are banked turns meant to be taken at higher speeds. The berm is a built up turn usually constructed of down logs, rocks, and soil. These features do cut down on braking and therefore erosion, but the construction of these features is more intrusive on the landscape.
Down Hill(DH) trails are traditionally 4’-8’ wide and meant to be ridden in one direction also. They are designed for heavier bikes and are usually highly technical in nature. Large rocks and roots typically punctuate these trails and can become erosional features. Down hill race courses are commonly mud-filled and tend to channel water as a result of the slope. Mud and rocks and roots are sought out by trail designers as technical features specifically for these types of trails. Down Hill trails are usually associated with ski resorts for the same reasons as are Freeride trails.
Bike Park/ Pump Track trails vary in width from 2’ to 8’. They are usually built on flat ground and are commonly found on municipal properties, in towns and cities, similar to skate parks. They can be considered playgrounds for people on bikes. Most have elevated features made of wood or metal and are completely synthetic in their design and construction. From the standpoint of environmental impact, these are mostly a concern in terms of extraction of the resources, chiefly wood and dirt.
The effects of mountain biking trails on wildlife run the spectrum from benign to catastrophic. In some places, wildlife follow mountain bike trails, especially where the mountain bike trails followed existing game trails. In winter, less effort is needed by wildlife to travel during heavy snow periods if they follow trails. However, this may favor some more opportunistic species, such as coyote, over shier species, like lynx. If the trails are groomed for winter riding, they can be heavily traveled by deer and other browsers. Again, though, in some places bike trails might be seen as attractive nuisances, if they favor opportunistic wildlife species over sensitive wildlife species.
On the other end of the spectrum are bike on animal collisions which can lead to animal fatalities. Salamanders, frogs, snakes, chipmunks, squirrels, weasels, and rabbits have been run over by careless trail riders or riders traveling at high speed. Larger animals can be reluctant to cross trails during daylight riding hours, but they are usually comfortable using and crossing trails at night. This is evident when studying footprints and scat left on trails by coyote, bear, fisher, and bobcat. On occasion, trail riders are injured by collisions with larger animals. A trail rider in Rennselaer County, NY was injured when he collided with a black bear. The bear swiftly recovered and fled the scene while the rider suffered minor abrasions and a bent front wheel.
The effects of mountain bike trails on soil and vegetation depend on the type of trail being built. XC trails usually result in minor soil compaction and initial increased soil erosion. Best practices can usually minimize soil erosion on any type of trail, but XC trails are usually sustainable. In almost all trail building scenarios large trees 6” or larger are considered natural features, so the trail is routed around the tree for aesthetic purposes. Freeride and DH trails are usually not as careful about vegetation avoidance. Higher speeds and the turning radius at those speeds may require some trees to be removed. Best practice will have trails reverse slope direction to scrub speed by a temporary uphill turn. This will allow for less vegetation to be removed.
The new trend in DH and Freeride trail building is more problematic. Machine built trails use small excavators, usually 4’ wide, tracked machines with an articulating cab that controls a 12-18” wide bucket. These machines are less likely to avoid trees and roots. On trails that traverse slopes, these machines sever roots and remove larger amounts of soil which can lead to increased erosion and topple trees that are leaning up or down slope due to the loss of a stabilizing root structure. These machines have been known to create 25 miles of trail in an eight-month period. Hand-built trails, due to their more carefully chosen line, may take up to 4 years to build a single trail of 12 miles.
The use of machines to build trails has for the most part been restricted to ski resorts and municipal properties. These trails are usually constructed by professional trail crews trained in best practices, but the size and slope of the trails usually make best practices difficult to adhere to.
The effects of mountain bike trails on water are similar to those of hiking trails. Depending on the slope, climate, and vegetation there can be increased turbidity and/or siltation, if the trail’s location is close to a stream. This increase in turbidity and siltation will have an adverse effect on water quality and breeding habitat for aquatic species, including trout and salmon. Best practices would keep any trail from paralleling a stream within 25’ of its banks. If a trail crosses a stream, best practices would mandate a bridge constructed of wood harvested from within the area and armored with stone on the entrance and exit from the bridge.
The newest threat to the environment from mountain bike trails is the emountain bike (eMTB). These electric powered pedal assist bicycles are heavy, and they may attain faster speeds for longer periods of time than a traditional mountain bike. Many conservationists have noted the increased distances a rider may travel in a day with an eMTB. While this is true in most cases, it’s fairly common for trail riders on traditional mountain bikes to cover 30-60 miles a day which is similar for eMTB’s. The real threat to the environment due to eMTB’s is the influx of new trail users who wouldn’t normally ride a mountain bike due to the difficulty. With this new influx comes the possibility that the riders of eMTB’s may not have the ethic of most mountain bike riders. That ethic says: Do not ride trails in muddy conditions. Do not skid into turns. Yield to uphill riders. Do not harass wildlife.
The new eMTB’s, in fact, seem to become almost indistinguishable from motorbikes. Newer eMTB’s have motors with 750watts of power and can travel at speeds of 28 MPH. It’s also touted that with minor adjustments to the motor, speeds of 46 mph are attainable. This has become such a contentious issue that the International Mountain Bike Association (IMBA) chose to oppose changes in the wording of the 1964 Wilderness Act that would allow for mountain bikes in Wilderness areas for fear it would become the slippery slope that allowed for any motorized vehicle to lawfully gain access to protected Wilderness areas. IMBA should support keeping all roadless areas free of mechanized recreation vehicles, but at least they took the right position on upholding existing language in the Wilderness Act. In the age of Donald Trump and his appointed heads of the Department of Interior and Department of Agriculture, it’s easy to connect the dots and see what are the motivations of the agitators who want to modify the Wilderness Act. Mountain bikers should not fall in with that selfish lot.
Many states have already adopted rules, regulations, and restrictions on ebikes on public land. It will be up to both conservationists and mountain bikers to encourage their state lawmakers to restrict these eMTB’s from public lands. They should be allowed on public roads, but not on foot trails or mountain bike trails and never off-trail.
As more cities and towns adopt mountain biking as an economic engine to boost tourism and economic development, it should be noted that most of these cities and towns are concentrating the trail construction on privately owned and municipal lands. Trails are kept close to town where riders may ride right from the center of town and return to enjoy the food and amenities the town has to offer. Examples of this model are Kingdom Trails of Burke, Vermont; and the city of Duluth, Minnesota, which claims to have 100 miles of trails within the city limits. Another example of this model is the city of Bentonville, Arkansas, which claims almost 100 miles of trails that can be ridden from the city and most of which are located in peoples’ backyards and formerly misused city-owned land that has been repurposed for mountain biking.
These models have chosen to leave open public land reasonably untouched and concentrate most of the trails close to or within the town or city. In these places, a rider can park his or her car and then can ride for days without having to drive anywhere. This idea is spreading to new trail development in most towns and cities that are trying to draw tourist dollars by becoming mountain bike destinations. Kingdom Trails has a user fee that is used to help pay the property taxes of landowners that allow trails on their property. This cooperative association has allowed landowners to keep their land intact instead of selling it to developers. This is beneficial to both the residents of Burke, VT and the wildlife that live in and pass through the area. If this model of mountain biking carefully concentrated on private and municipal lands spreads, it could also lessen pressure to open public wildlands to mountain bikes.
Jason Kahn recently joined The Rewilding Institute board of directors after retiring from serving as a bike mechanic after retiring from serving as an Earth Sciences teacher. Jason continues to cycle regularly and is plotting a bicycle-supported wildways trek next year with his rewilding friends.