Effects of Cultivation and Grazing Exclusion on the Soil Macro-faunal Community of Semiarid Sandy Grasslands in Northern China

Abstract

Cultivation and overgrazing can cause desertification of sandy grasslands in arid and semiarid regions. However, little was known about their effects on soil macro-fauna. In this study, we described the soil macro-faunal community structure at cultivated, grazed, and ungrazed sites in the semiarid Horqin steppe, northern China. Soil bulk density was 1.61 g cm−3 at grazed sites, similar to that at cultivated sites. Cultivation reduced soil organic carbon and total nitrogen by 36 and 46%, respectively, compared with grazed grassland. Grazing exclusion decreased soil bulk density and pH by 16 and 3%, respectively, and increased soil moisture, soil organic carbon and total nitrogen by 75, 22, and 4%, respectively, compared with grazed grassland. Cultivated and grazed sites had similar group richness (9 and 10 groups, respectively) and Shannon's index (1.98 and 1.93, respectively); both were significantly lower there than at ungrazed sites. Simpson's index at grazed sites was 0.18, markedly higher than at ungrazed (0.12) and cultivated (0.16) sites. There were no significant differences in soil macro-faunal density among the three treatments, although the density at grazed sites was 24% higher than at cultivated sites and 30% lower than at ungrazed sites. Soil bulk density, electrical conductivity, pH, and the C/N ratio significantly affected the community structure. Specific macro-faunal groups responded to the different living conditions by adaptation to or selection of specific habitats. For example, the Thomisidae, Reduviidae, Staphilinidae, and Curculionidae responded negatively to increasing soil bulk density and all of these except the Curculionidae responded negatively to increasing soil temperature. These groups have important implications for the soil food web, and thus for the soil ecosystems. Our results suggested that cultivation and continuous grazing negatively affected soil properties and macro-faunal diversity, whereas livestock exclusion enhanced soil macro-faunal assemblies and improved their biodiversity. Changes in these assemblies might be potential indicators of ecosystem recovery and management impacts. Supplementary materials are available for this article. Go to the publisher's online edition of Arid Land Research and Management to view the supplemental file.