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Mountain Biking: A review of the ecological effects, The Miistakis Institute, Faculty of Environmental Design-University of Calgary, For Parks Canada, February 2010

Note: Please note that the full report is only available in English. To have access to the report or if you need more information, please contact Julie Lefebvre from the Activities and Facilities team, by email or at 819-934-1113.

Executive summary

In order to inform an activity assessment of mountain biking within Canada’s national protected heritage places, Parks Canada commissioned the following literature review on the ecological effects of mountain biking. The purpose of this review was to summarize the nature of the ecological perturbations or effects arising from the disturbance of recreational mountain biking.  Extensive searches and cross-references were conducted using the most relevant on-line databases available through the University of Calgary library.  Searches of the World Wide Web via leading search engines and focused reviews of known mountain biking and trail associations were also conducted.  The intent of the initial search was to identify as many papers, reports and theses as possible that addressed topics related to mountain biking.  Source materials were then filtered to identify those references that addressed ecological effects of the activity. The research described in this report is concurrent with a complementary effort to understand the demographics, culture, and social effects of mountain biking as a recreational activity.

Mountain biking is a popular and burgeoning recreational activity. Compared to other outdoor recreational activities, there is a relative dearth of understanding and peer-reviewed scientific papers on the ecological effects of mountain biking.  The original objective of this literature review was to provide a comparison of published research on the relative effects of four distinct sub-disciplines of mountain biking: cross country, freeride, downhill and bike parks/dirt jumps.  However, the lack of published literature focusing on the sub-disciplines, or the comparison between them, made this impossible. Therefore, the review provided herein primarily addresses cross-country riding.  Specific effects associated with mountain biking activity and infrastructure characteristic of the other types of use have emerged as a considerable gap in the research literature.

The literature review was conducted within the framework of recreation ecology – the study of the biophysical effects of recreational activity.  One of the most important theoretical generalizations arising from recreation ecology is referred to as the curvilinear use-impact relationship.  In simple terms, the nonlinear nature of the use-effect relationship suggests that the greatest proportion of ecological effect is generated during the initiation and early use period of a new facility or infrastructural development.  This phenomenon has been clearly established for a wide variety of soils and vegetation responses to activity, and suggests that the majority of the environmental effect occurs when a trail is first developed or constructed.

The review followed the approach used in the majority of the recreation ecology literature, exploring the ecological effects of the activity on soils, vegetation, water and wildlife individually.  Although this framework provides a useful structure in which to discuss the effects of recreation, it is essential to recognized that there are connections, feedbacks and synergies between the categories.  Ultimately, effects of disturbance must be addressed with an understanding of the cumulative and synergistic nature of their occurrence.

The available published literature indicates that mountain biking as an anthropogenic disturbance is similar in its environmental effects as other forms of summer season trail use.  The effects of mountain biking on soils and vegetation have received the most attention and experimental examination of the four categories.  Research has mainly focused on quantifying erosion (created by shear forces) and compaction (created by normal forces) that result from mountain bike use and combine to create "tread incision". Other concerns include water runoff and resulting sediment transport (erosion), and trail widening to avoid muddy or puddled areas.  As with other forms of trail-based recreation (hiking, horseback riding), research has shown that the soil type (erodability), terrain relief and amount of moisture have the greatest influence on the significance of mountain biking effects on soils.  Researchers also reported that cycling technique and skill level influences the level of impact on soils, with braking/skidding and cutting switchbacks creating the most damage. Vegetation trampling and removal generally follows the curvilinear use-effect relationship described above with de-vegetated trails appearing even after relatively low levels of use.  Mountain bike trails as vectors for the spread of non-native exotic plant species has been identified as a concern, but little empirical work is available to draw any conclusions beyond the knowledge that exists for other similar hiking and horse trails.  The current review was unable to find any published research on the effects mountain biking on water quality.

The effects of mountain biking on wildlife are primarily related to habitat alteration as a result of impact to soils and vegetation, as well as disturbance of daily or seasonal habitat use.  The significance of the disturbance is related to the type, timing, intensity, duration and spatial distribution of use.  One of the most significant characteristics of mountain biking as a form of wildlife disturbance is a result of the potential relative speed and silence of the activity.  A relatively fast moving, quiet mountain biker may approach an animal without being detected until well within the normal 'flight response zone'.  The result may be a severe startle response by the wildlife species with significant consequences to the animal and/or the mountain biker.  In the case of grizzly bears, such incidents may result in aggressive behaviour toward the mountain biker. In the case of bison, elk and pronghorn antelope, one study did not reveal a significant difference between hikers and mountain bikers with respect to the reaction of any of the three species to their presence.

This review clearly identifies significant gaps in the available literature to assess the ecological effects of mountain biking.  Some of the most important knowledge gaps include: 1) To date, there have been few documented interdisciplinary studies of the environmental and social effects associated with mountain biking; 2) Very little has been studied of the recreational ecology of mountain bikes in the Canadian context. Since many of the environmental effects are known to vary according to regional geophysical traits, applying research carried out in other biomes and landscapes may be problematic.  Similarly, there are few studies outside of mountainous and high relief terrain areas; 3) No specific research has been published on the water-related environmental effects of mountain biking; 4) Some more focused study of the effects of mountain biking on wildlife would be of benefit; 5) Existing research focuses mainly on the type of recreational activity with little or no emphasis on the timing, intensity, duration and spatial distribution of the activity.  Furthermore, there is little in the literature to differentiate between different types of mountain biking; 6) There is a tremendous need for research that addresses the cumulative effects of human recreational activity in protected areas.  This includes the need to identify thresholds associated with numbers, timing, type and distribution of use.