Effects of long-term grazing exclusion on plant and soil properties vary with position in dune systems in the Horqin Sandy Land

Grazing exclusion is an important policy currently being employed by the Chinese government to recover degraded grasslands. Despite many field experiments, controversy still exists concerning the effects of grazing exclusion on the restoration of sand dune ecosystems. In order to examine the response of plant and soil parameters to grazing exclusion, a 32-year field experiment was conducted in active dune systems in the Horqin Sandy Land. The results showed that the dominant species changed significantly at the windward and leeward sides of dunes, and at interdune lowlands after long-term grazing exclusion. Plant density, cover, species richness, and soil organic carbon and total nitrogen (N) significantly increased across all topographic locations in areas with grazing exclusion. The effects of grazing exclusion on plant and soil parameters varied as a function of position in the dune system. In general, the recovery of plant and soil parameters occurred more rapidly at the windward side than at the leeward side when grazers were excluded. Soil organic carbon and total N were positively correlated with plant community density, cover, and species richness in active and stabilized sand dune systems. In addition, grazing exclusion strengthened the relationship between soil and plant parameters. The results showed that the effects of grazing exclusion on plant and soil properties were strongly dependent on dune position. These findings should prompt those responsible to assess the recovery of sand dune systems by synthesizing the effects of multiple positions within a dune system.