Deterioration of the physical structure of trails results from both natural processes and the forces exerted by trail users. Some studies indicate that natural degradation erodes trails more than trail users. The opposite is also sometimes true: User-caused erosion can exceed natural processes where use is heavy or soils are particularly weak.
Empirical studies have looked at natural degradation processes throughout the globe. Leung and Marion (1996) in their literature review looked at these various studies and found that a trail surface's susceptibility to erosion depends on the soil texture, trail width, dead vegetation width, the amount of vegetation cover relative to bare area, the slope angle and climate.
