The influence of vegetation structure on saltation threshold was investigated using uniformly spaced arrays of non-erodible roughness elements on a bed of erodible sand in an wind tunnel. Structural variables tested using arrays of solid cylinders included element aspect ratio (height/diameter) and lateral cover (total frontal-silhouette area per unit ground area). In agreement with previous studies, increase in saltation threshold above the value for bare sand was strongly related to lateral cover. Increasing aspect ratio from 0.25 to 4 tended to enhance the increase in saltation threshold at a given lateral cover. An approximate fit to the results could be obtained using a relation proposed by Raupach et al. (Journal of Geophysical Research, 1993, 98D, 3023–3029). Porous elements were constructed as clusters of narrow, vertically oriented cylinders (model ‘stems’), forming porous model plant bodies that were cylindrical in overall shape. Low-porosity elements were found to be approximately 50 per cent more effective in increasing saltation threshold than either solid or high-porosity elements. The ratio of plant-body frontal-silhouette area (based on overall dimensions) to total stem frontal-silhouette area was found to be a useful measure of plant-body porosity for wind erosion studies. Some conventional measures of vegetation amount fail to account for changes in vegetation structural attributes that may strongly influence aeolian processes.
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Musick et al. (1996) studied this question.
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