EFFECT OF HILLSLOPE ANGLE AND SUBSTRATE ON TREE TILT,AND DENUDATION OF HILLSLOPES BY TREE FALL |
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| Authors: | Hugh H Mills |
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| Institution: | Department of Earth Sciences , Tennessee Technological University , Cookeville, TN 38505 |
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| Abstract: | Although the question of whether tilted trees indicate hillslope instability has been discussed by previous authors, few systematic measurements have been made. In Giles County, Virginia, tree-tilt measurements were made on 30 trees at each of seven sites. Sites included topographic noses, side slopes, boulder streams, and talus, with slope angles ranging from 6° to 39°. Trees on steep boulder streams are tilted more than those on noses or side slopes with comparable slope angles, but this difference could result from a difference in tree types. On one very steep (39°) fine-grained talus, however, tilt of all types of trees is great, the average tilt from the vertical being 29.1°. Tilt at this location probably reflects slope instability, although evidence suggests that this instability is not simple creep. In a second study, calculations were made of the importance of tree fall for hillslope erosion. The volumes of all tree-fall pits within a 4-hectare area on a steep shale nose were measured, and, using assumptions of previous workers, an erosion rate of 13 mm/1000 yr was calculated. This value is an order of magnitude lower than one value reported previously. |
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