Abstract:

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.

Key words: sand prevention and control, low vegetation coverage sand control, hydrological principle, deep soil water infiltration, recharge groundwater