黄土区次降雨条件下林地径流和侵蚀产沙形成机制——以人工油松林和次生山杨林为例

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0～20cm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-A case study of artificial P. tabulaeformis and secondary natural P. dadidiana stands

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·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 slope-land,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.