低覆盖度治沙理论的核心水文原理概述

土壤水分的渗漏过程是陆地生态水文的3个最核心过程之一，降水向土壤深层渗漏或者补给地下水，关系到干旱沙区水平衡维持和植被稳定持续发育。多年的治沙实践和研究结果表明：（1）天然分布稳定的沙生植被，覆盖度一般低于30%，降水均能够渗漏到土壤深层或者补给地下水；（2）人工营造的固沙林，当林分的覆盖度大于40%后，林下土壤含水率逐步降低，降水不能够渗漏到土壤深层或者补给地下水，林木出现衰败或者死亡；（3）低覆盖度固沙林设计出了带间的土壤渗漏补给带，确保了降水能够渗漏到深层或者补给地下水，固沙林及其带间植被能够稳定持续发育；（4）在极端干旱区，基本上没有降水能够渗漏到2 m以下土层，灌溉才能确保林分的稳定持续；在干旱区，深层渗漏水量占年降雨量的1%—13%，半干旱地区的深层渗漏水量占年降雨量的11%—23%，半湿润干旱区的深层渗漏水量占年降雨量的15%—45%，能够确保沙区的水平衡和雨养植被的稳定持续发育。这也是低覆盖度治沙理论最基本的生态水文原理，为中国防沙治沙事业开拓了新领域、新方向和新思路，对推动中国今后的防沙治沙工作有着重要意义。

Overview of hydrological principle of low vegetation coverage sand control

Deep soil water infiltration is one of the three most important processes （runoff， infiltration and evapotranspiration） of terrestrial ecology and hydrology. Maintaining water balance and supporting vegetation in arid sandy areas depends on how much rainwater can penetrate into deep soil layer or recharge groundwater. Review of our past research shows： （1） Natural vegetation in desert usually covers less than 30% of the landscape. Precipitation can infiltrate into deep soil layer and recharge groundwater. （2） In sand-fixing forest land， if the plant coverage exceeds 40%， soil moisture gradually decrease， rainwater can not penetrate into the deep soil layer and recharge groundwater， and the vegetation eventually degrades or dies. （3） Low-coverage shelterbelts designed allow more rainwater penetrateing into the soil between forest belts， which can be beneficial for soil and vegetation recovery between belts， and promote sustainable afforestation. （4） In extreme arid areas where the precipitation cannot penetrate more than 2 m depth， irrigated afforestation is the only way to sustain vegetation. If deep soil water infiltration reaches 1%-13% of annual rainfall in arid areas， and 11%-23% in semi-arid areas， and 15%-45% in sub-humid arid regions，under these circumstances，the regional water distribution reaches a equilibrium and rain-feed vegetation can be sustained. These are the basic ecological hydrology principles of combating desertification with low vegetation coverage， which is of great significance to promote further desertification control and the construction of sand-fixing forests in northern China in the future.