Effectiveness of sand-fixing measures on desert land restoration in Kerqin Sandy Land, northern China

Abstract

In the semi-arid Kerqin Sandy Land of north China, land desertification and frequent sand storms in the spring strongly affect the growth of grassland vegetation and crops, and give rise to large reductions in yield as a result of wind erosion and sand dune movement. To bring desertification under control and reduce its influence on grassland and farmlands, many measures have been developed and implemented for stabilizing mobile sand dunes and restoring desertified grasslands. This study was conducted from 1996 to 2003 to evaluate the effectiveness of desert land restoration after implementation of sand-fixing measures. The results showed that construction of straw checkerboards and planting of shrub seedlings significantly enhances topsoil development on the dune surface, increasing silt and clay content and facilitating accumulation of soil carbon and total N, as well as accelerating an increase in plant diversity, vegetation cover and plant density. These findings suggest that using straw checkerboards and planting shrubs are successful methods for mobile sand dune stabilization and desertified grassland restoration in semiarid regions. The mechanism creating these changes is a reduction in wind erosion and improvement of the soil environment for plants. In addition, our results showed that construction of straw checkerboards was slightly more effective in vegetation and soil restoration in comparison with planting shrub seedlings, especially at the primary stage.

Introduction

Desertification, a human-induced land degradation process occurring primarily in fragile ecosystems of arid, semi-arid and dry sub-humid climatic areas, is one of most serious environmental and socioeconomic problems worldwide and a major threat to the sustainability of agriculture and economic development (Lal, 2000, Wang, 2000). Desertification-affected land exceeds 3.9 × 10⁵ km² in China (Wang, 2000); 61.3% of this desertification was caused by wind erosion. Kerqin Sandy Land, located in the agro-pastoral transition zone between the Inner Mongolian Plateau and the Northeast Plains, has suffered severe desertification since the mid-1970s primarily due to improper exploitation and wind erosion. Desertification and frequent sand storms in the spring strongly affect the growth of grassland vegetation and crops and give rise to large reductions in yield as a result of wind erosion and sand dune movement (Zhang et al., 2004).

To bring desertification under control and reduce its influence on grassland and farmlands, many measures have been developed and implemented successfully in China (Zhu et al., 1988). Among these, constructing wheat-straw checkerboards and planting indigenous dune-adapted shrubs are accepted as common measures to restore vegetation on desertified sand dunes (Fan and Zhou, 2001). These measures have been confirmed to be successful in accelerating land restoration, decreasing wind erosion, improving soil characteristics and facilitating plant establishment and spread. However, the relative effectiveness of these two measures has not been well studied, and evaluating this can provide environmental managers a basis for formulating appropriate and resource-efficient land restoration plans. This study seeks to evaluate the relative effectiveness of these measures on land restoration at representative sites.

Numerous studies have demonstrated the impact of sand-fixing measures on degraded land restoration (Fullen and Mitchell, 1994, Whitford, 2002, Su and Zhao, 2003, Li et al., 2004a, Li et al., 2004b). Many results have shown that in arid and semi-arid sand dune systems, the use of straw checkerboards for dune stabilization can increase the entrapment of airborne dust, enhance the fine particle content of topsoil, increase water-holding capacity and soil fertility, and improve other soil physicochemical properties that promote the establishment and spread of plants (Xu et al., 1998, Qiu et al., 2004, Li et al., 2006). In addition, several studies have demonstrated that once a population of indigenous shrubs has been established, it will act as a sink for resources, either actively through root uptake of soil water and nutrients (Hook et al., 1991, Gutiérrez et al., 1993, Burke et al., 1995) or passively by accumulating wind-blown dust and litter (Barth and Klemmedson, 1982, Buckley, 1987, Garner and Steinberger, 1989), in a feedback mechanism that facilitates invasion and colonization by other plant species under or near its canopy. However, very limited studies have been conducted to compare the effectiveness of different sand fixing measures for desert land restoration. Zhang et al. (2004) compared the effects of sand fixing measures on plant diversity, vegetation cover, plant biomass, and soil properties in the two years following implementation of these measures, and concluded that constructing wheat-straw checkerboards and planting indigenous shrubs were the best practices in Kerqin Sandy Land. But relatively long-term effects of sand-fixing measures on desert land restoration still remain unclear, especially the rate of soil and vegetation recovery and the succession of plant communities. Therefore, an 8-year study was implemented to monitor the changes in soil and vegetation associated with sand-fixing measures in Kerqin Sandy Land. The objective of this paper is to evaluate the long-term, relative effects of two different sand-fixing measures on restoration of mobile sand dunes in a semi-arid region.