Long-term effects of revegetation on soil water content of sand dunes in arid region of Northern China

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Abstract

Desert is a challenging environment for organisms largely controlled by extreme abiotic factors including soil water content. The objectives of this study were to: (1) determine the effect of vegetative water utilization on soil water content; and (2) monitor the long-term vegetative response to the change of soil water content after establishing the revegetation of sand dunes of the Shapotou Region in the Tengger Desert, Northern China. The permanent revegetation plots were established in different sites in 1956, 1964, 1976 and 1982. Soil water content was monitored at 20 cm intervals of 10–300 cm in depth. Water content in sand dunes, was measured gravimetrically after 24-h desiccation at 105°C during the entire period of revegetation through the year to 2000. Our data show that soil water contents rapidly decreased at 9–10 years after revegetation, and similarly the vertical profile of soil water contents also decreased by depth. Annual precipitation is positively correlated with the water contents at depths 0–40 cm, although no clear-cut relationship was shown between precipitation and soil water at the deeper soil layers (from 40 to 300 cm). It is therefore concluded that water utilization of different plant species: shrub with deep-rooting system and annual plants with shallow-rooting system influences the spatial distribution of water inside the soil profile. Temporal and spatial variances of soil water also affected the changes in composition, coverage and biomass of vegetation. Vegetation composition of dominant species has successively changed from all shrub species, such as Caragana korshinskii and Hedysarum scoparaium to annual plants and shrub with shallow-rooting system (Artemisia ordosica). The shrub biomass also changed along with soil water content, although the biomass of herb species increased over time. After 45 years, the shrub coverage decreased from the highest average 30.21% to the current level of 6%, whereas herb coverage increased over time. The soil water content was, however, kept relatively constant at lower level (1.23%) despite shrub coverage was reduced to about 6%. These results provide important baseline information for establishing vegetation and utilization of limited water resource in arid desert regions.

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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