Long-term effects of revegetation on soil water content of sand dunes in arid region of Northern China
Introduction
Desert soils in an arid rain-fed environment have low and limited water contents, in which soil water availability is the prime factor limiting the number and size of perennial plant species and thus is the main constraint in permanently controlling desertification (Nash et al (1989), Nash et al (1991); Berndtsson and Chen, 1994; Berndtsson et al., 1996; Chen et al., 1996; Southgate et al., 1996). As China is one of the most desertified countries in the world, desertification threatens about 3.3 million km2 of land where the lives of 400 million people are involved (Chen et al., 1996; Zha and Gao, 1997). It was well known that revegetation is one of the most effective methods to reduce the hazards of desertification (Shapotou desert research and Experiment Station, Chinese Academy of Sciences, 1986). Thus, since 1950s large areas of arid desert regions of China were reclaimed by artificial vegetation. It may be predicted that the stability of current vegetation will be threatened by water-table fall and deterioration (Mitchell et al (1996), Mitchell et al (1998)). Hence, it is very important that potential variation of soil water contents be understood in order to sustain the vegetation in arid desert regions. In this paper, the soil water variation and its relation to the succession of plant community over past 45 years after revegetation was established on dunes by the contemporary straw checkerboard technique in Shapotou region, southeastern edge of Tengger Desert in China (Fig. 1).
Section snippets
Study site
The Shapotou of Ningxia Hui Autonomous Region, southeast edge of the Tengger Desert (37°32′ N and 105°02′E) with an elevation of 1339 m a. m. s. l. (Fig. 1), is a steppe desert zone with an ecotone between desert and oasis (Shapotou Desert Research and Experiment Station, Chinese Academy of Sciences, 1986; Li et al., 1998). The mean temperature is −6.9°C in January and 24.3°C in July. The first frost occurs in late September and the last frost in mid-April. The temperature on the sand surface
Results and discussion
The variation of dune soil water contents is mainly controlled by climatic conditions as well as the properties of underlying rock and groundwater (Zhang and Shi, 1998). The process of soil water content changes in dunes is chiefly influenced by precipitation and evaporation at macroscopic level that include two aspects: (1) the infiltration and evaporation of water under potential energy force and (2) the thermo-osmosis and condensation of vapor controlled by heat conduction and heat diffusion
Conclusions
The temporal variation of soil water contents in vegetated areas of Shapotou region showed a decreasing trend along with the establishment, development and evolution processes of sand-fixing vegetation. In the early period after vegetation was established, soil water changed actively with season influenced by precipitation and inactively afterwards; 9–10 year later from vegetation establishment soil water content in 100–300 cm layer has decreased from 3.8% to 3.5% in early period to about 2%,
Acknowledgements
We gratefully acknowledge two anonymous reviewers for providing valuable comments on the manuscript. This work was supported by the National Natural Scientific Foundation (90202015) and Innovation Project from Chinese Academy of Science (project No. KZCX3-SW-324).
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