Population dynamics of Agriophyllum squarrosum along an ecosystem restoration chronosequence in the Tengger Desert, China: Indication implications for desertification combating

Agriophyllum squarrosum, an annual native herb pioneer species, is associated with shifting sand dunes along the southern edge of the Tengger Desert, China. Its population dynamics shift with the restoration of sandy desert ecosystems after shrub planting. A chronosequence of four sites was evaluated on the southern edge of the Tengger Desert: an untreated shifting sand dune, and three formerly shifting sand dunes planted with shrubs 5, 15, and 25 years previously. Five years after planting, density of A. squarrosum was unchanged but the relative cover was only 6.0% of that found on the shifting dune. After 15 years, density and cover were less than 1% of the shifting dune. After 25 years, A. squarrosum had completely disappeared. During the 25 years of plant community development, the factors associated with the A. squarrosum decline included a decrease in the seed bank, improvement in the topsoil, biological crust formation, and photoinhibition of seed germination. A. squarrosum declines as more stable plant community recover and this population decline tracks the improvements in site quality and can be regarded as an indicator of desertification reversion