Metro is the regional government in the Portland, Oregon area. Thanks to the region’s voters, the agency has acquired approximately 17,000 acres of natural areas to protect water quality, wildlife habitat and connect people with nature. The goal of this document is to better understand the trade-offs between different types and levels of recreational access in the context of our work to protect habitat and water quality, and provide access to nature in a growing urban area. Only by thoroughly understanding the effects of recreational activities on wildlife and water quality are we able to avoid, minimize and mitigate potential harm to the resources we are committed to protecting.
Recreation ecology is the scientific study of environmental impacts resulting from recreational activity in protected natural areas. The nature of a literature review is to summarize what has been studied, what has been learned, and what the experts have concluded. This document reviews the literature on overall and relative effects of three user groups – hikers, mountain bikers and equestrians – on trails, habitat, and wildlife to help inform ecologically appropriate placement and construction of trails in natural areas. Studies are reviewed from the U.S. and elsewhere, with a focus on soft-surface trails in natural areas. We included limited information about other non-motorized trail user groups such as trail runners and beach walkers. Motorized off-road vehicles were omitted from this review because they are generally not allowed on natural area trails within the urban and near-urban region. A previous literature review on the effects of dogs on wildlife and water quality is included as Appendix 1.
Studies vary in terminology for our recreational groups of interest. In this report “hiker” generally means a person walking along a trail for various reasons such as exercise, wildlife watching or moving between places. “Mountain biker” refers to a non-motorized bicycle rider on a soft or natural surface trail; alternative terms in the literature include off-road bicyclists or off-road cyclists. “Equestrian” refers to a person riding a horse on a trail. Throughout the text we refer to these as “user groups.”
Trails provide people with important opportunities to improve health and well-being, and providing access to nature is especially important in urban areas.[2-5] However, as indicated in various literature reviews, trails and trail use can damage natural areas including negatively affecting soils, vegetation, water quality, plants, and animals.[6-27] Damage to trails or habitats and negative effects on wildlife are more likely when trails are inappropriately located, designed, constructed, maintained or used, or when unauthorized trails are allowed to proliferate. These issues can also increase trail maintenance costs[28-30] and negatively affect visitors’ experience.[31-33]
This document reviews the types of recreational effects in Chapters 2-7, including information about user group-specific effects. Each chapter includes a summary of key points. Chapter 8 offers information on how to minimize, monitor and manage effects. Throughout the review we provide representative study examples with additional citations.
We paid close attention to the effects of recreation on wildlife (Chapters 6 and 7) because they are less well documented than physical effects such as erosion or vegetation damage. Scientific names for species mentioned in the text are in Appendix 2. For wildlife, human disturbance increases animals’ stress and can cause them to hide, change behavior or flee. Some species, such as those that do well in urban areas, are generalists and can tolerate human disturbance. Other species such as pregnant animals, long-distance migrants, and habitat specialists tend to be more stressed and displaced by trail users. Some species may permanently leave a natural area.
Figure 1 illustrates the relationships between environmental, trail design, recreational use and their effects on trail damage, water quality, vegetation damage and wildlife...