热带北缘裸地与桉树林地降水-地表侵蚀特性的对比研究

A COMPARATIVE STUDY ON THE CHARACTERISTICS OF PRECIPITATION SURFACE SOIL EROSION IN BARE LAND AND EUCALYPTUS FOREST LAND OF NORTH TROPIC REGION

本文研究了水滴动能与地表侵蚀的相互关系问题，通过对相邻的两个地类：没有任何植被的光裸地和地表同样光裸但有人工桉树林的２个试验小集水区的对比研究，说明了单位雨量下的侵蚀强度与水滴动能存在最为紧密的关系。裸地地表的侵蚀强度决定于大气降水动能，而桉树林地的侵蚀强度却主要与林冠的穿透水水滴动能成正相关。总的说来，桉树林林冠的存在加大了林地所接受的降水动能，特别是在中小降雨强度的情况下更是如此，这就说明了营造人工林时。

The relation between water drop kinetic energy and surface soil erosion has been studied here. Two types of land surface have been taken into consideration, they are bare land without any vegetation on it and eucalyptus forest land without any undercover. The results showed that there was a close relation between water drop kinetic energy and soil erosion intensity of unit rainfall, and the water drop kinetic energy was the direct factor which caused the soil erosion of land surface. For bare land, its erosion intensity was determined by atmospheric raindrop kinetic energy. However, for eucalyptus forest land, it was relative to throughfall water drop kinetic energy and had no relation with that of atmospheric rainfall. Throughfall kinetic energy can not be affected by atmospheric precipitation intensity, but it is determined by the structure of forest canopy (including tree species, canopy density, leaf area index, height of canopy etc). And thus, when atmospheric precipitation intensity in open place is smaller, the parameter λ (in %) will be larger, which means that the forest canopy will enlarge the soil erosion of forest land. Correspondingly, when atmospheric precipitation intensity in open place is larger, the parameter λ (in %) will be smaller, which means that the forest canopy will reduce the lashing of waterdrops to forest land, and thus, have the positive effects on soil conservation. The value of λ changes with atmospheric precipitation intensity, rainfall, height of canopy and canopy density. The characteristics of soil erosion for these two studied areas were different. Soil erosion from the eucalyptus forest land was mainly caused by the rainfall with middle and small precipitation intensity, but that from bare land was mainly caused by the rainfall with heavy precipitation intensity. As a whole, the canopy of eucalyptus forest increased the impact of water drop to land surface, especially in the situation of middle and small intensity of atmospheric precipitation. This study explained that we should consider the influence of forest canopy structure on forest land erosion when making plantation.