Relationship Between Surface Soil Erosion Rate and Soil Physical Properties in a Mountain Forests-Arid Valley Ecotone
山地森林－干旱河谷交错带表层土壤侵蚀率与土壤物理性质的关系

Soil erosion is the main cause of land degeneration,and can be considered a natural disaster restricting human survival and development of the global environment. Using field investigations and laboratory analyses,surface soil erosion rate and the relationship between soil erosion rate and soil physical properties in dry valleys of the upper Minjiang River were studied. We found severe soil erosion and an average erosion rate of 27.58% across vegetation types. Soil erosion was the most serious for Robinia pseudoacacia,and minor for the conversion of farmland to Minjiang cypress. The soil erosion rate of Robinia pseudoacacia was 3.28 times that of conversion of farmland to Minjiang cypress. Soil erosion rate was correlated with the structure ped breaking ratio(SPBR). The clay ratios were less than 0.30 for the different vegetation types,and soil coarsening was widespread. Sand and coarse silt content were significantly higher than those of fine silt and clay content,and clay content was lowest. Average organic matter content was 45.73 g/kg for topsoil. Soil erosion rates were correlated with soil organic matter content,>0.25 mm water-stable aggregate content,aggregate mean weight diameter (MWD) and geometric mean diameter (GMD) after wet sieving. The change characteristic of stable aggregate content and organic matter content showed synchronization. Strengthening existing shrub and natural secondary forest protection,reducing human disturbance,and implementing natural recovery would contribute to the accumulation of soil organic matter in the mountain forests-arid valley ecotone. These measures would inhibit the expansion of the dry valley and extend the ecological functions of subalpine forest. This study reveals the essence of soil erosion and provides a theoretical basis for ecological construction and the conversion of farmland to forest.