黄土区次降雨条件下林地径流和侵蚀产沙形成机制

以黄土区两种常见森林植被(次生山杨林和人工油松林)长期定位观测试验为基础，从水量平衡和径流产沙机理出发，分析了次降雨条件下两种林地和荒地坡面产流产沙过程.结果表明，次降雨量在5.0～50.0 mm范围内，油松林和山杨林的林冠和枯枝落叶层总截留率分别为15.45%～56.80％和20.56%～47.81％，且随降雨量的增大而减小.与荒坡地相比，林地土壤入渗性能显著增强，尤其是0～20 cm土层.分析表明，在一般降水条件下林地无径流产生;而在降雨雨强为2.5 mm·min^-1和历时30 min条件下，山杨林地无地表径流产生，荒坡地的径流流速和径流挟沙浓度均为油松林地的23.5倍，而其径流剪切力和径流能量均为后者的8倍；油松林地的径流量和产沙量比荒地分别减少了87.6%和99.4%，与径流小区多年(1988～2000)观测平均值(分别为87.0%和99.9%)相近.

Generation mechanism of woodland runoff and sediment on Loess Plateau under hypo-rainfall

Based on the long-term observation and from the viewpoints of water balance and runoff-and sediment generation, this paper studied the generation processes of runoff and sediment on two typical woodlands, artificial P. tabulaeformis and secondary natural P. dadidiana, and uncultivated slope-land in Loess Plateau under hypo-rainfall. The results showed that within the range of 5.0 - 50.0 mm rainfall, the total interception of canopy and litter was 15.45 % - 56.80 % for P. tabulaeformis and 20.56% - 47.81% for P. dadidiana, and decreased with increasing rainfall. Woodlands had a higher soil water infiltration capacity than uncultivated slope-land, especially in 0-20 cm soil layer. Both the two woodlands did not generate runoff under regular rainfall. Under the assumed rainfall of 2.5 mm x min(-1) intensity and 30 min duration, P. dadidiana stand did not produce runoff, but the runoff velocity and sediment-carrying capacity of uncultivated slope-land were 23.5 times, and runoff shearing stress and energy were 8 times as much as P. tabulaeformis stand. The runoff-and sediment generation on P. tabulaeformis stand decreased by 87.6% and 99.4%, respectively, compared with those on uncultivated slopeland, which was well accorded with the average observed value in runoff plots during 1988 - 2000. The theoretical analysis on the generation mechanism of woodland runoff and sediment may be effective to evaluate the benefits of forest in soil and water conservation.