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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.
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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.