Soil Erosion

The most common problem observed on hiking trails is soil erosion, albeit multiple trailing, the widening of trails, and puddling are issues as well (Cole, 1987). Usually, hiking trails are compacted with easy to follow paths, and are accompanied by identifiable edges of where nature meets paved path. However, the soil on the path can become loosened; thus causing particles of soil to loosen and disrupt the compactness of the path (Deluca et al., 1998). Through this process, the soil on the trail becomes eroded and excessive foot traffic accelerates the process even further. 

An important factor to consider is the type of forest hiking trails are located in. Different habitats experience different catalysts of soil erosion. The aforementioned soil loosening process is applicable to habitats that have dry trails. If hiking trails experience heavy rainfall, then the impact resulting from foot traffic can be increased runoff.

Soil erosion on a trail in Lebanon Hills

This leads to a consistent downward flow of water that carries sediment along with it (Lal, 1994). The flow of water then erodes the trail over time, giving it a new shape. 

Unlike the effect of trampling, the impact of hiker traffic on a trail's loosening of soil does not increase over time. Rather, it looks to decrease in the effect of impact. In his research of the impact of hiking boots on woodland trail, Fred R. Kuss observed more soil loosening after initial hiker traffic than later hiker traffic (Kuss, 1983). This decrease in impact can be attributed to the possibility of management re-compacting trail paths. 

Sources

Cole, D. N. 1987. Research on soil and vegetation in wilderness: A state-of-knowledge review. Pages 1350177 in R. C. Lucas (comp.), Proceedings, national wilderness research conference: Issues, state-of-knowledge, future directions. General Technical Report INT-220. USDA Forest Service, Ogden, Utah.
Deluca, T. H., W. A. Patterson Iv, W. A. Freimund, and D. N. Cole. "Influence of Llamas, Horses, and Hikers on Soil Erosion from Established Recreation Trails in Western Montana, USA." Environmental Management 22.2 (1998): 255-62.
Kuss, F. R. 1983. Hiking boot impacts on woodland trails. Journal of Soil and Water Conservation 38: 119-121.

Lal, R. 1994. Soil erosion research methods, 2^nd ed. Soil Water Conservation Society, Ankeny, Iowa.
Soil Erosion photo: http://www.lebanonhills.com/sustainable-trails/