Karst soil erosion process was studied through analyzing the anatomical characteristics of exposed and unexposed tree root and dating exactly exposed times of the tree root which grow in Guizhou Puding karst area. Results show that average sensitivities of tree ring width are larger than 0. 2, which means tree ring recorded environmental information. Tree ring widths of unexposed root are not changed from pith to bark, and vessels size is nearly the same and evenly distributed in each ring. Of the same tree the inner tree ring width, vessel lumen area, and fiber lumen area of exposed root are the same with the unexposed ones, while the exterior demonstrates extremely variance, the tree ring width narrower, the vessel and the fibre lumen area smaller, and most of tree roots are eccentricity. The root exposed time could be exactly identified based on all the former changes; the root exposures were happened respectively from 1996 to 2007. Soil erosion amounts of exposed root recorded decline from 2002 to 2007, and average erosion amount is 0. 464 t · a-1 , that is to say, exposed root well recorded soil erosion process.
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