A review of formation mechanism and restoration measures of "black-soil-type" degraded grassland in the Qinghai-Tibetan Plateau

The aim of this paper was to review the formation mechanism and restorative measures of the black-soil-type degraded grassland ecosystem of the source area of Yangtze and Yellow Rivers, Qinghai-Tibetan Plateau. The relationship among plants, animals, soil, climate change, human activity and the black-soil-type degraded grassland was analyzed based on a review of literature and report of previous investigations conducted by the authors. Degradation of the black-soil-type grassland was caused by a set of complex factors such as altitude range, district characteristics and weather conditions, which existed for a long period of time. Livestock overgrazing and climate dryness were the dominant factors that caused the degradation of the grassland in question. In addition, damages done by rodents, especially pikas (Ochotona curzoniae), via burrowing through the turf and gnawing at herbs have sped up the formation process of the degradation of the black-soil-type grassland. Furthermore, with the inflation of the population in the last 20 years, the influence of human activity on grassland degradation cannot be neglected. Based on the different successive stages of degradation of the black-soil-type grassland ecosystem, different restorative measures were suggested. The lightly and moderately degraded grasslands should be kept away from disturbance, such as fencing closure, weeding, fertilizing, using rodenticide, decreasing stocking rate, optimizing population structure stocked and slaughter ages; whereas the artificial and semi-artificial grassland establishment required to restore ecosystems should be applied to heavily and extremely degraded grasslands.