Causes and Countermeasures of Soil Drying under Artificial Forest on the Loess Plateau in Northern Shaanxi

Returning cultivated land back to forest in the Loess Plateau is a great unprecedented engineering, and its successfully implementation has very important actual significance to the restoration of ecological environment deteriorated seriously and can decrease flood in the lower reaches of the Huanghe River. At present, soil drying is the sever problem in afforestation, which results in artificial forest not growing well and even withering. The field survey and the data analysis show that the cause of soil drying in the Loess Plateau of northern Shannxi has two aspects: natural causes and anthropogenic causes. Natural causes include the less normal rainfall, the further decreasing rainfall and the increasing temperature in recent 50 years. Anthropogenic causes include destroying vegetation, the great density of artificial forest, the afforestation in unsuitable areas, and not obeying the regularity of vegetation succession. Based on the present situation in the Loess Plateau, the paper suggests that measures that combine the natural vegetation restoring with sparsely re\|afforestating should be taken to restore the forest vegetation in the broadleaf forest zone southward from Yanan to the southern rim of the Guanzhong basin; measures that combine planting grass and bush predominantly and planting tree in large interval should be taken to restore the forest vegetation in the forest\|steppe zone between Yanan and the Great Wall; measures of mainly planting grass should be taken in the zone northward from the Great Wall. In afforestation it is necessary to take water\|harvesting engineering measures such as building pits arranged like fish scales for raising the survival rate of arbor and ensuring normal growing of artificial forest.