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

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 105degreesC 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 0-40cm, 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 and desert regions. (C) 2003 Elsevier Ltd. All rights reserved.