A classic example is the stream or river corridor through a city. Because of historic flooding and old economies, many waterways in cities offer the last undeveloped wildlife habitat - all the more critical because it is riparian habitat, which so many need. This is also a favorite place for people to recreate, and a zone where streets and buildings don't block trail routes. It also notes the potential positive impacts. Trail development is often accompanied by trash clean-up, removal of incompatible land uses, and ecological restoration.
Trails can serve as a foundation of political support for wildlife.
Among the many case studies presented in the book, the cleanup and trail development of Sand Creek in Denver stands out as having obvious benefit. The river flows through industrial areas and suffered impacts. Trail builders are repairing streambanks and educating people about the existing problems. Such impacts must be weighed with the benefits of the trail. The book covers key ecological concepts such as the zone of influence, edge effects, habitat fragmentation, landscape patterns, habitat quality, and species diversity.