Evolutionary characteristics of the artificially revegetated shrub ecosystem in the Tengger Desert, northern China

The rain-fed sand-binding vegetation which stabilizes the migrating desert dunes in the Shapotou area at the southeastern edge of the Tengger Desert was initiated in 1956. The shrubs initially employed were predominantly Caragana korshinskii, Hedysarum scoparium, and Artemisia ordosica, and a desert shrub ecosystem with a dwarf shrub and microbiotic soil crust cover on the stabilized sand dunes has since developed. Since 1956 the success of this effort has not only ensured the smooth operation of the Baotou-Lanzhou railway in the sand dune area but has also played an important role in the restoration of the local eco-environment; therefore, it is viewed as a successful model for desertification control and ecological restoration along the transport infrastructure in the arid desert region of China. Some of the effects of recovery from desertification and ecological restoration on soil properties are shown by the increase in the distribution of fine soil particles, organic matter, and nutrients. The physical surface structure of the stabilized sand dunes, and inorganic soil crusts formed by atmospheric dust, have also led to the gradual formation of microbiotic soil crusts. Sand dune stabilization is associated with: (1) decreased soil particle size, (2) increased total N, (3) increased thickness of microbiotic crusts, (4) increased thickness of subsoil, and (5) an increase in volumetric soil moisture in the near-surface environment. After 17 years of dune stabilization, both the number of shrubs and community biomass decreased. The number of microbes, plant species and vegetation cover, all attained a maximum after the dunes had stabilized for 40 years. There is a significant positive correlation between the fractal dimension of soil particle size distribution (PSD) and the clay content of the shallow soil profile in the desert shrub ecosystem; the longer the period of dune stabilization, the greater the soil clay content in the shallow soil profiles (0-3 cm), and the greater the fractal dimension of soil PSD. This reflects the fact that during the revegetation processes, the soil structure is better developed, especially in the upper profile. Hence, the migrating sand dune becomes more stabilized. Therefore, the fractal model can be used to describe the texture and fertility of the soil, and, along with the degree of stability of the previously migrating sand dunes, can be used as an integrated quantitative index to evaluate the revegetation practice in the sand dune areas and their stabilization.