Influence of historic sheep grazing on vegetation and soil properties of a Desert Steppe in Inner Mongolia

Grazing intensity and grassland degradation in China has increased with a growing livestock population. The Desert Steppe is vulnerable to the impacts of livestock because of relatively short and sparse ground cover and sandy soil. This study investigates the effects of historic sheep grazing on the vegetation and soil properties of a Desert Steppe community.The experiment was conducted at three sites (replicates) in Siziwang Banner in Inner Mongolia with four treatments defined along an historic grazing gradient: ungrazed (control), lightly grazed (LG), moderately grazed (MG) and heavily grazed (HG). The grazing treatments were classified based on species composition and ground cover. The vegetation and soil properties in each treatment and replicate were assessed in fall 2005. The vegetation total N (TN) and P (TP) concentrations and delta N-15 levels were not affected (P > 0.05) by grazing. Grazing increased (P = 0.02) soil bulk density but had no effect on soil TN and TP concentrations or 815 N levels (P > 0.05). However, HG resulted in 16.4, 11.4 and 7.6% reductions in soil organic carbon (OC), TN and TP concentrations, respectively. Grazing had no effect (P > 0.05) on the concentrations of soil available P, available N (NO3- and NH4+), electrical conductivity, pH or soluble ions (Na+, K+, Ca2+, Mg2+, Cl- and SO42-). The vegetation of the Desert Steppe is generally tolerant of grazing pressure but is relatively unproductive, supporting a smaller number of livestock than the more mesic grasslands. Therefore, treatment differences were generally not detected. However, the combination of sandy soils (similar to 70%) and generally reduced litter and plant cover with increased grazing pressure suggests that the Desert Steppe is vulnerable to soil erosion. This risk may be reduced by ensuring appropriate grazing pressure and animal distribution with judicious herding. (c) 2008 Elsevier B.V. All rights reserved.