Soil erosion on mountain trails as a consequence of recreational activities. A comprehensive review of the scientific literature.

This article reviews the scientific literature on trail erosion and the magnitude of the erosive processes that occur on mountain trails due to recreational activities, mainly due to hiking. This work is necessary as a result of the increase in hiking and biking in forest, scrubland and grasslands, and the soil and vegetation degradation induced by these activities. We analysed results that have been compiled in the scientific literature, as well as other issues such as the geographical and temporal distribution of the research, the methods applied, the journals where the research was published, the types and quantity of uses of the pathways and the measures undertaken for damage mitigation. This paper highlights that there is a need for harmonization of methods. The results show that soil erosion rates are highly variable, high, and non-sustainable. Trail erosion research is growing at a rate of 3 papers per year and is published in a small group of scientific journals. Six journals published 47% of the papers on trail erosion, which show a high concentration in environmental journals. There are few papers published in the soil science and geomorphology disciplines, although the research topic and the science background are in these two disciplines. Reported world soil losses from trails ranged from 6.1 Mg ha y to 2090 Mg ha y, all of which are not sustainable. Trail erosion has mainly been investigated in the USA and is a new topic in other regions of the world. There is a need to implement mitigation measures to avoid land degradation, and this should be researched in the near future as right now most of the research describes and quantifies the problem but does not provide solutions: mitigation, rehabilitation or restoration. From a pure scientific approach, we claim that there is a need to research the connectivity of flows and the role of the trails on runoff generation and then sediment yield at pedon, slope and watershed scales. There is a need to research the mechanisms of the soil erosion process in trails: trampling effect, wheel impact, factors and seasonal and temporal changes.