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Riparian Vegetation Effects on Freeze-Thaw Cycling and Desiccation of Stream Bank Soils
Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org
Citation: Paper number 032129, 2003 ASAE Annual Meeting . (doi: 10.13031/2013.14008) @2003
Authors: Theresa Wynn, Saied Mostaghimi, H.E. and Elizabeth F. Alphin
Keywords: Subaerial processes, riparian buffers, stream bank erosion, freeze-thaw cycling, desiccation
Riparian vegetation is frequently used for stream bank stabilization, but the effects of
vegetation on stream bank erosion have not been quantified. Subaerial processes, such as
desiccation cracking and freeze-thaw cycling, are climate-related phenomena that deliver soil directly
to the stream channel and make the banks more vulnerable to flow erosion by reducing soil strength.
This study compares the impact of woody and herbaceous vegetation on subaerial processes by
examining soil temperature and moisture regimes in vegetated stream banks.
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Soil temperature and soil water potential were measured at six paired field sites in southwest Virginia
for one year. Differences in daily minimum and maximum soil temperatures, daily temperature
range, and average daily soil water potential were compared for both summer and winter. Results of
this study showed that stream banks with herbaceous vegetation had higher soil temperatures
overall and a greater diurnal temperature range, as compared to forested stream banks. These
differences decreased during the growing season as the herbaceous vegetation matured.
Additionally, increases in daily average soil water potential of 13% to 57% were observed under
herbaceous vegetation, as compared to woody vegetation, likely due to the evapotranspiration from
the shallow herbaceous root system on the bank face.
In contrast to summer conditions, the deciduous forest buffers provided little protection for stream
banks during the winter: the forested stream banks experienced diurnal temperature ranges two to
three times greater than stream banks under dense herbaceous cover and underwent as many as
eight times the number of freeze-thaw cycles. With the absence of a dense canopy, the stream
banks under mature forest cover were exposed to solar heating and night time cooling, which
increased the diurnal soil temperature range and the occurrence of freeze-thaw cycling.
Results of this study suggest that in areas with soils susceptible to desiccation cracking, woody
vegetation may provide the best protection against degradation by subaerial processes. In areas
with silty soils prone to freeze-thaw cycling, a dense groundcover may provide more protection
against soil loss due to freeze-thaw cycling than just deciduous woody vegetation.