摘要
乌江流域坡耕地是水土流失的主要来源，以单行稀疏地埂树为主的传统坡耕地农林复合植被类型，除能起到一定的固坡护埂作用外，对坡面径流影响甚微，不能有效控制水土流失。为此，提出了分带营造坡耕地水保防护林的方法，在坡面配置上引入临界坡长的概念，采用临界坡长作为配置防护林带的间距，根据林带间耕地的产流携沙量确定林带宽度。考虑到林带间距较密，遮荫胁地影响突出，因此以林带充分发挥防护功能，在不改进耕作方式的情况下，营建土地单位的粮食总产量不减为前提，确定林带高度的上限值，从而在山区混交农林的研究上第一次找到求算不同耕地类型（基岩特性、坡度、土层厚度等）营造防护林带的带距、带宽和带高上限值，并以此为依据进行合理树种选择和搭配的有效办法。
In Wujiang River watershed, upland is the main source of soil erosion. In this area, the main upland agroforestry pattern is planting trees sparsely along natural earth dike. Apart from stablizing the dikes to somewhat extent, patterns of this kind have little influence on hindering runoff on the slopes,thus they wouldn't have much effect on controlling soil erosion. For this reason, we put forward an agroforestry model of interplanting trees in contour strips on upland with crops. In arranging these shelter strips on upland, we quote the concept of critical slope length, which is dependent on soil texture, slope and rainfall characteristics, using it as the distance between shelter strips and determine shelter strip breadth in accordance with the runoff and sediment yielding from the upper crop belt. Considering that the distance between shelter strips is relatively short and this would cause over-shade and coercion problem, we determine a upper limit for the height of trees to be planted in various types of upland on the premise that the total crop yield wouldn't decline after the shelter strips bringing into full play of their protective function in case that tillage technique don't change. In this way, we find out an efficient method to calculate the distance between shelter strips, shelter strip breadth and upper limit of shelter strips on different types of upland which are classified by factors such as parent rock properties, slope and soil depth, etc. and on this basis select suitable tree species and assemble them rationally for the first time in the study of upland agroforestry in mountainous area.
