黄土区林草植被与降水对坡面径流和侵蚀产沙的影响

The Effect of Vegetation and Precipitation upon Runoff and Sediment Production in Sloping Lands of Loess Area

在一定地形地貌基础上，林草植被与降水是决定坡面产流产沙量的主要因素，而这些因素各因子之间合作用于坡地产流产沙，增加了影响机制的复杂性。为深入分析降水因子与林分结构因子对坡地降雨产流产沙的影响，为黄土区植被建设提供理论依据，对蔡家川流域典型样地的实验资料进行分析。结果表明，刺槐和油松林场降雨产流、产沙置与降雨量和降雨强度有较好相关性，但相关性随着林分郁闭度的增大而减小；当油松林林分郁闭度〈0．6时，产流、产沙量与I30的相关性要更显著于与I10的相关性，而林分郁闭度在0．6以上时，则相反。在林分结构因子对坡面产流产沙的影响中，当林分覆盖度〉40％时，林分减水减沙效益显著。林地枯落物和草本植物通过截持降水、增加地表糙率来削减坡面产流产沙量，刺槐和油松林地的枯落物年截流量占降雨总量的13．5％～22％。刺槐和油松林的稳渗速率随林分密度的增加而增大，但不与密度的增加幅度成正比，当刺槐、油松林的密度超过3000株/hm^2时，稳渗速率增加缓慢。从防蚀角度考虑，可将其作为林分密度的上限。在林分生物量〉14．51 t／hm^2时，植被具有极好的防护功能。通过对影响坡面产流产沙的影响因子的灰色关联分析，林分郁闭度和草本、枯落物生物量对坡面产流产沙影响显著，关联度值均〉0．6。

Without regard to the function of terrain, vegetationand precipitation both are the main factors who determine runoff and sediment amount, and the mechanismof runoff and sediment yielding is becoming more complex for daughter factors from vegetationand rainfall act on together. In order to study the effect of precipitation and vegetationon runoff and sediment production, experimental data from typical sample plots of Caijiachuan watershed were analyzed, which will provide theoretical basis for vegetation construction in Loess area. The results showed as follow ： 1 ） Bettercorrelative relationship between rainfall and rainfall intensity and runoff and sediment production from Robinia pseudoacaciaforest and Pinus tabulaeformisforest were testified by multiple regression, but the correlation decreased gradually with the increase of canopy density. When canopy density of Pinus tabulaeformisforest was less than 0.6, the correlative relationship between runoff and sediment production and Isowere more dramatic than that of I10. While it was more than 0.6, the result was contrary to the former. 2） Effect of forest stand in decreasing runoff and sediment production was dramatic when coverage of forest stand was more than 40%, however, it was weaker when coverage not exceeding 60%. 3） Runoff and sediment production from sloping lands were cut down because of the function of litter and herb in intercepting rainfall and promoting roughness. To Robinia pseudoacaciaforest or Pinus tabulaeformisforest, interception amount was about 13.5 -22 percent of all precipitation. 4） Ultimate infiltration capacity increased with the increase of the density of forest stands, but the increasing range of the former was not direct ration to the latter. And it increased very slowly when the density of Robinia pseudoacaciaforest or Pinus tabulaeformisforest exceed 3 000 trees/km^2. Therefore, the density of 3 000 trees/km^2 may be regarded as upper limit of stand density while the function of preventing erosion is only taken into account. 5） The forest stand with biomass of 14.51 t/hm^2 had dramatic effect in preventing erosion. 6） Based on gray congnate analyse to kinds of factors affecting runoff and sediment production in sloping land, the factors of stand canopy density and herb and litter biomass were the most significant ones, whose gray incidence degreesall exceeded 0.6.