Physiographic components of trail erosion
Godwin, Ian Chandler Paterson
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No previous study has sought to discriminate between soil erosion and soil compaction when explaining the "missing" cross-sectional areas of incised trails, assuming instead that erosion was the dominant process. Separating the two processes of erosion and compaction is critical to understanding the relationship between physiographic variables and the structure of trails. The purposes of this project are to estimate the relative effects of compaction and erosion on trail cross sectional area along the New World Gulch Trail, Montana, and to better understand the relationship between erosion, compaction, local topography, vegetation, soil bulk density, and soil texture. The following hypotheses were addressed: 1) adjusting the incised cross sectional area of a trail, by removing the effects of soil compaction, will increase the amount of variance in erosion explained by collected physiographic variables; and 2) inclusion of soil bulk density and soil texture as physiographic variables will increase the amount of variance in cross-sectional area explained along the trail. The goals of this study required the collection of field data, analysis of soil samples, and statistical analysis of data. Soil samples and other field measurements were collected over several months during the summer and fall of 1994. Some of the topographic information used in the statistical analysis originated in Urie's (1994) study of recreational trails. The determination of trail slope as one of the primary components of trail incision is consistent with previous studies. Soil water content is the second most significant independent variable when the percentage of particle sizes are not considered. Percent vegetative cover is also significant in the stepwise regression, although it is not significantly correlated to cross-sectional area. The most significant variable added to those already studied was soil bulk density. When individual variables were regressed against the measured cross-sectional area, off-trail soil bulk density accounted for the second greatest amount of variance (r2 = 0.12) after trail slope (r2 = 0.35). The ratio of on-trail soil bulk density to off-trail soil bulk density, which could be considered a measure of compaction, accounted for even more variance (r2 = 0.18) than soil bulk density.