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Variation in Root Density Along Stream Banks

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org

Citation:  Paper number  032131,  2003 ASAE Annual Meeting . (doi: 10.13031/2013.14009) @2003
Authors:   Theresa Wynn, Saied Mostaghimi, Adrian Harpold, Marc Henderson, Leigh-Anne Henry
Keywords:   Riparian buffers, stream bank erosion, root-length density

While it is widely recognized that vegetation plays a significant role in stream bank stabilization, the effects have yet to be fully quantified. Many of the benefits of riparian vegetation are associated with the root systems. Roots bind the bank soil in place and act as fiber reinforcement, reducing soil erosion and increasing bank stability. The goal of this study was to determine the type and density of vegetation that would provide the greatest protection against soil erosion by determining the distribution and density of roots in stream banks.

To quantify the distribution and density of roots along alluvial stream banks as a function of riparian buffer vegetation type and density, 25 field sites in the Blacksburg, Virginia area were sampled from June through August 2002. The riparian buffers varied from short turfgrass to mature riparian forests, representing the full range of possible vegetation types. Root-length density (RLD) with depth and above ground vegetation density were measured at each site. The sites were divided into two groups, forested and herbaceous, based on aboveground vegetation. Differences in root density and distribution were determined using nonparametric statistics.

For both riparian buffer types, roots extended to depths in excess of one meter. At the herbaceous sites, very fine roots (diameter < 0.5 mm) were most common and over 75% of all roots were concentrated in the upper 30 cm of the stream bank. Under forested vegetation, fine roots (0.5 mm < diameter < 2.0 mm) were more common throughout the bank profile, with 55% of all roots in the top 30 cm. In the top 30 cm of the bank, herbaceous sites had significantly greater total RLD than forested sites ( = 0.01). While there were no significant differences in total RLD below 30 cm, forested sites had significantly greater concentrations of fine roots, as compared to herbaceous sites ( = 0.01).

Research has shown that the ability of a soil to resist fluvial erosion is related to the quantity of fine roots in the soil (Kamyab, 1991). This suggests that forested vegetation may provide better protection against stream bank erosion than herbaceous vegetation. More research on the effects of root density on soil erodibility is required to confirm this conclusion.

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