Trail sustainability: A state-of-knowledge review of trail impacts, influential factors, sustainability ratings, and planning and management guidance.

Protected areas (PAs) provide many important recreational, social, and economic benefits that are largely dependent on their ability to sustain visitation. Trail networks are a critical tourism infrastructure element that directly accommodate high quality recreation activities and experiences while providing access to and protection of irreplaceable natural and cultural resources. Unfortunately, most trail networks consist of historic "legacy" trails that were not sustainably designed and whose intensive use cause unacceptable impacts to PA resources, experiences, and values. This paper provides an international state-of-knowledge review of trail science research within the field of recreation ecology to describe common trail impacts and factors that influence trail degradation that trail stewards can manipulate to enhance the sustainability of trail networks. Two emerging models that seek to rate trail topographic sustainability are presented to illustrate their potential utility to PA managers. Expanding and incorporating trail science research into the sustainable trail planning, design, and Best Management Practice literature are also discussed.