黄土丘陵区森林保持水土效益及其机理的研究

Study on Benefits of Soil and Water Conservation of Forest and Its Mechanism in Loess Hilly Region

刺槐、柠条、沙棘、沙棘×油松、沙棘×小叶杨幼林到郁闭成林的蓄水保土效益变化分３个阶段。１～３年生为低下阶段，有侵蚀性降雨就会发生水土流失；４年生为由低到高的过渡阶段，蓄水保土效益迅速增加，５年生以上为效益显著阶段。一般在无大暴雨情况下基本不发生水土流失，且６０％的林分覆盖度对减少土壤侵蚀量的作用显著。各郁闭成林的枯落物蓄积量和容水量以沙棘及其混交林最多，刺槐林中等，柠条林最少。并且枯落物的厚度是增强土壤抗冲性效应的重要指标。同时森林改善了土壤物理性质，使土壤容重变小，入渗和抗冲性增强。

Three stages have been divided to benefits of soil and water conservation from thicket to cover-overheaded of Robinia pseudoacacia, Caragana microphylla, Hippohae rhamnildes,Hippophae rhamnoides and Pines tabulae fomis,Hippophae rhamnoides and Populus simonii carr.Benefits of soil and water conservation is low in 1-3 year and during this Period soil and water loss will be occured if there have erosive rainfall. In 4 year its benefits of soil and water conservation increase rapidly. The period over 5 year is the one which benefit is very significent. There is no erosion occured if there have no heavy storm and the forest coverage of 60% has important role to reduce soil loss amount. The accumulated litter amount and holding water capacity among all coveroverheaded forests, Hippophae rhamnoiles and its mixed forests are highest, Robinia pseudoacciais medium, and Caragana microphylla is lowest,, An important index of improving soil anti-scourability is thickness of litter. Meanwhile, forest can improve soil physical properties, decrease soil density,and increase soil infiltration and anti-scourability.