Effects Of Vegetation Cover On Runoff And Sediment Reduction On Slop Land In Karst Areas Of Guizhou Province

Located in the center of the karst area in southwest China, Guizhou is one of the most serious soil erosion provinces in the westward; it exacerbated the degree of rock desertificationconstantly. Rainfall is the main driving factor to cause soil and water loss, reasonable regulation and control of slope runoff is the key to prevent soil erosion. In this study, based on the rainfall, runoff and sediment data obtained from the field runoff plots experimental observation, analysis of water erosion characteristics on slope land in karst area, and evaluation of the effects of different vegetation cover on runoff and sediment reduction on slope land in karst area of Guizhou provence were carried out by using of theory and methods of mathematical statistics and modeling simulation.During the observation period, the annual rainfalls in the study areas were well-distributed, but the monthly rainfall was uneven during a year, which formed a distinct rainy season and dry season. There was a good positive correlation between the runoff, sediment yield and rainfall on the bare slope, and the correlation coefficients were0.81and0.73, respectively.The runoff depth and single parameter of rainfall (rainfall amount P or maximum rainfall intensity of30min I30) had no significant power function relationship on slope lands covered by different vegetations. When considering P and I30together, the power function relationships between the runoff depth and the rainfall parameters enhanced significantly.Runoff and sediment yield have power function relationship with rainfall (P), maximum rainfall intensity of30min (I30) and slop gradients (s). The sediment yields on slope land meet linear function with the runoff on slope lands.With the increase of slope gradient, runoff and sediment yields on slope farmland increased while runoff and sediment reduction effects decreased. When the slope gradient was13°, runoff and sediment reduction effects on slope farmland was better than other vegetations, indicating that it is suitable to develop crop farming within appropriate slope gradient. The runoff and sediment yields increased significantly with the increase of slope gradient. When the slope gradient reached25°, sediment yields on the slope farmland increased dramatically, it became the main sediment source.Most types of forests and grasses vegetation in the study area had experienced three periods:no effect, partial effect and remarkable effect on runoff and sediment reduction, it indicated that runoff and sediment reduction effects of vegetation is a gradual process. Canopy and ground cover played a major role in runoff reductuin while vegetation roots played a major role in sediment reduction.The results showed that runoff and sediment reduction effects of different vegetation were:economic forest> artificial pasture> water conservation forest.The same vegetation with different allocations (planting density, mixing mode) made different effects on runoff and sediment reduction. The same vegetation with identical allocations also made different effects on runoff and sediment reduction if they were planted in different regions. Therefore, types, allocations and planting regions of vegetation should be considered equally to achieve the best soil and water conservation effects.In order to effectively control soil erosion on slope land in karst areas in Guizhou province, on the farmland with smaller slope gradient less than25°, according to the needs of the agriculture and economic development to adjust agricultural structure and develop economic forest industry base on the local conditions, and to decrease crop planting areas gradually by allocating of slope farmland crops and forest trees proportion. The economic forest has not only the effect on runoff and sediment reduction, but also can bring better economic benefits to local residents; it meets their needs of living and can prevent their destructive activities like deforestation on steep slope lands. When the slope gradient of farmland reaches25°, the policy measures of returning farmland to forest (grass) should be thoroughly implemented, and to develop water conservation forest or other economic forest, and grassland and animal husbandry.