Trail Based Recreation and its Impacts on Wildlife




Trail-based outdoor recreational is often overlooked when considering human-driven changes to the Colorado Rocky Mountain landscape. But recent research suggests trail-based recreation may have a greater impact than originally believed. As population and participation in outdoor recreation continues to increase so does the demand for more trail and access to Colorado’s wild places. Trail-based recreation such as hiking, horseback riding, mountain biking, and ATV’s are shown to increase stress levels in native wildlife, decrease and fragment habitat, as well as acting as conduits to exotic plant spread. Each impact disrupts natural ecosystem functions and further degrade the integrity of the ecosystem as a whole. To minimize impact more education is needed to inform recreationalist on their impacts and what they can do to minimize and preserve the landscapes they enjoy. Also, minimizing motorized and mechanized recreation can significantly improve and restore a landscapes natural function.


Many people move to Colorado for its abundant outdoor recreation opportunities. A 2018 statewide study indicated that 92% of Colorado residents participate in some form of outdoor activity at least once every few weeks (CPW 2019). Outdoor recreation has increased in popularity dramatically since 2019. The Outdoor Foundation reported 7.1 million more Americans participated in the outdoors in 2020 than in 2019, making it the largest one-year jump on record and accounting for a total of 160.7 million recreational users.  And according to the Colorado State Demography Office, Colorado’s current population sits at 5.7 million and is predicted to reach 8 million by 2050 (CPW 2019). How might this increase in population and recreational activity impact Colorado’s wildlife and natural ecosystem functions? Many studies suggest outdoor recreation and the construction of trails can decrease species diversity, fragment habitat, displace wildlife, introduce and spread invasive species, and decrease survival and reproduction rates in big game mammals.

This drive and desire to be outside comes from a place of love and admiration for the outdoors. Outdoor recreation has, after all, been the gateway into environmental activism for so many and is assumed to be compatible with conservation. But when Colorado Parks and Wildlife (CPW) estimates that 3,464 more miles of new trails will need to be added to Colorado’s 39,000 miles of established trails to keep pace with the growing population its compatibility must be called into question. It is highly important for trail-based recreationalist to understand and mitigate their environmental impacts when enjoying the outdoors.


The lure of economic gain from the outdoor recreation industry may persuade forest land managers and municipalities to increase trail and route density. In the recent proposal from the Outdoor Alliance for the revision of the Grand Mesa, Uncompahgre, and Gunnison National Forests management plans, the organization requested to, “Create and improve connectivity between existing routes…while creating a diverse network of new route opportunities of varying mileage and skill level.” Currently, the areas under revision, aside from a couple game management areas in the Gunnison National Forest, are below their target elk and mule deer populations with below average cow to calf ratios (CPW 2020). The Uncompahgre is also home to one of the few remaining indigenous bighorn sheep herds (S-21) in the state of Colorado and are believed to be well-below their historic population numbers (Diamond & Banulis, 2012). These declines in big game wildlife populations are primarily due to habitat loss and human disturbance from domestic livestock, human & energy development, and recreational use.

Studies indicate, trail and route density are directly correlated with habitat fragmentation and compression (Wisdom et al,. 2018). In areas where trails overlap and intersect the avoidance area for big game animals dramatically increases (Wisdom et al,. 2018). Mechanized (mountain bikes) and motorized (ATVS, dirt bikes, snowmobiles) recreational use has the greatest impact on game animals, altering their feeding, resting, and travel patterns (Naylor et al, 2009). A US Forest Service and State of Oregon study determined the distance in which elk will flee from different types of recreationalists: hiking 400 meters, horse 550 meters, mountain biking 750 meters, and ATV 1,350 meters (Wisdom et al., 2018). The increased heart rate and stress from such disturbances can be energetically costly especially during gestation, calving, and essential foraging periods and seasons. Fleeing or hiding in dark timber means less time foraging and food uptake essential to winter survivability and may cause a decrease in cow to calf ratios (Phillips & Alldredge, 2013). Researchers have observed similar detrimental energetic costs on grouse during their most vulnerable time from winter recreation such as backcountry skiing and snowmobiling (Arlettaz et al., 2015).

Hiking, mountain biking, horseback riding, and motorized off-road vehicles are also major conduits of invasive species transport and spread. A 2020 study calculated the potential of hiker’s clothing as vectors for seed transport, dispersal, and germination in South Africa (Smith & Kraaij, 2020). Researchers collected debris and seeds from the shoes of 262 trail runners competing in four different running races during the pre-registration period. A total of 33 different plant species were collected. What they found was more than half of the seeds collected were exotic plant species (Smith & Kraaij, 2020).  Still, off-road vehicles and horseback riding are shown to have significantly higher impacts on non-native spread and excessive soil compaction and erosion due to their heavy weight (Pickering et al., 2010; Anderson et al., 2015).

The proliferation of non-native and invasive plant species can decrease and outcompete essential forage for native wildlife and disrupt pollination processes (Inouye, 2020). Invasive species spread, especially that of smooth bromegrass or cheat grass can create monoculture areas altering fire regimes and increasing combustion and spread rates (Inouye, 2020).


Recreation does not need to stop but changing the way in which we recreate can have a multitude of positive impacts. Educating recreationalist and requiring them to remain on established trails, minimize excessive noise, and keep domestic dogs on a leash can help to minimize their impact. Boot washing stations and informational signs at popular trailheads may decrease transport and spread of invasive species. Shoe washing should also be a requirement at all competitive events as well as education around why it is an important practice. The installation of trail counters may also be useful data for researchers in determining trail usage intensity and how that may impact wildlife.

Increasing environmental buffers through restoration efforts may decrease the efficiency of spread. In a 2019 Chile study it was observed that trails with a forest barrier along the trail edge had little to no non-native presence (R. Lieftke et al., 2019). Most non-native species are adapted to meadows and open space, not the low light availability in a forest’s understory.  Volunteer tree planting and restoration initiatives along already established trails may reduce the propagule pressure. Maintaining and incorporating forest buffers should also be a consideration in the construction of new trails. 

Expanding designated wilderness, as proposed in Alternative D in the GMUG forest revision plan, will help restore fragmented landscapes and provide stronger protection against future development and human disturbance. Intact habitat blocks abundant in forage and cover as well as associated migration and movement corridors should remain protected and are avoided by trails and roads. The development of trails should be limited to areas where human activity and trail densities are already high; not expanded into relatively undisturbed areas. Maintaining and reducing route densities to less than one mile per square mile may decrease impact and maintain habitat (Wisdom et al., 2018). It is also recommended the Forest Service coordinate and work with State and private landowners to increase and improve connectivity in the GMUG region.


Recreation will always have some level of impact on natural ecosystems. But through education and the development of mitigation strategies impact can be minimal. The answer is not to build more trails in the few pristine areas that remain in Colorado but to utilize and improve areas already experiencing high activity and disturbance. Finding an appropriate balance to support the recreation economy and biodiversity conservation is difficult and there is possibly not a perfect solution. But through further research and the collaboration between government and private land managers/owners it is possible to achieve sustainable recreational practices.


Anderson, L. G., Rocliffe, S., Haddaway, N. R., & Dunn, A. M. (2015). The role of Tourism and Recreation in the spread of non-native species: A systematic review and meta-analysis. PLOS ONE, 10(10).

Arlettaz, R., Nusslé, S., Baltic, M., Vogel, P., Palme, R., Jenni-Eiermann, S., Patthey, P., & Genoud, M. (2015). Disturbance of wildlife by outdoor winter recreation: Allostatic stress response and altered activity–energy budgets. Ecological Applications, 25(5), 1197–1212.

Banulis, B. Diamond, B. (2012). Bighorn Sheep Management Plan. Colorado Parks and Wildlife. Retrieved November 21, 2021 from,

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GMUG Draft Environmental Impact Statement for the Land Management Plan Revision. (2021) U.S. Forest Service.

Inouye, D. W. (2019). Effects of climate change on alpine plants and their pollinators. Annals of the New York Academy of Sciences, 1469(1), 26–37.

Liedtke, R., Barros, A., Essl, F., Lembrechts, J. J., Wedegärtner, R. E., Pauchard, A., & Dullinger, S. (2019). Hiking trails as conduits for the spread of non-native species in mountain areas. Biological Invasions, 22(3), 1121–1134.

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Phillips, G. E., & Alldredge, A. W. (2000). Reproductive success of elk following disturbance by humans during calving season. The Journal of Wildlife Management, 64(2), 521.

Pickering, C. M., Hill, W., Newsome, D., & Leung, Y.-F. (2010). Comparing hiking, mountain biking and horse riding impacts on vegetation and soils in Australia and the United States of America. Journal of Environmental Management, 91(3), 551–562.

Smith, K., & Kraaij, T. (2020). Research note: Trail runners as agents of Alien Plant Introduction Into Protected Areas. Journal of Outdoor Recreation and Tourism, 31.

Wisdom, M. J., Preisler, H. K., Naylor, L. M., Anthony, R. G., Johnson, B. K., & Rowland, M. M. (2018). Elk responses to trail-based recreation on public forests. Forest Ecology and Management, 411, 223–233.


About Brittany Parker

Habitat Stewardship Coordinator for BHA

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