Natural Grassland Productivity and the Livestock-Feeds Balance in Qinghai Province

Grassland ecological systems play a fundamental role in the terrestrial system.Grassland degradation can lead to a series of environmental problems,such as soil erosion and sandstorm. Achieving dynamic grassland monitoring and performing evaluation of forage-animal production balances are of great importance to the implementation of grassland sustainable development.The authors evaluated forage-animal production balances over Qinghai Province,which is rich in grasslands and located in the eastern Qinghai-Tibet Plateau.The area of usable pasture areas ranks fourth in China,and the annual production of sheep and other livestock ranks fourth and fifth, respectively.In this study,observed grassland yield data were obtained from GPS.Continuous 16-days composites of Moderate-resolution Imaging Spectroradiometer(MODIS)-Normalized Difference Vegetation Index(NDVI)images of 500 m spatial resolution were acquired.Natural grassland yield estimation models and models for estimating theoretical livestock carrying capacity of 8 prefectures in Qinghai Province were established based on these data sources.Considering reality of seasonal use of natural grasslands in this region,the maximum livestock carrying capacity of natural grasslands were analyzed.Supplementary forage was calculated from by-products from farming and forest recorded in Qinghai Statistical Yearbook.In terms of actual livestock carrying capacity derived from statistical data,the carrying capacity of natural grasslands or supplementary forage and the actual number of livestock were compared.Results showed that the total natural grassland productivity was 125.521×106t in Qinghai in year 2007 and the grassland yield in Haibei Prefecture was largest,indicating a value of 45.9×106t.Haidong and Xining Prefectures had the least yield,being 1.95×106t and 1.73×106t,respectively.The largest livestock carrying capacity of natural grassland was found to be in Haibei Prefecture,being about 8.56× 106sheep units.The natural grassland carrying capacity of Haidong and Xining was smaller than other prefectures.Excluding supplementary forage,the overgrazing rates of natural grasslands in Xining,Haidong,and Hainan exceeded 100%.With considering the carrying capacity with the use of supplementary forage,overgrazing rates of 50%-100%were found in Xining,Haidong, Huangnan,and Yushu.A balance between livestock carrying capacity and actual number of livestock was shown in Haibei and Haixi Prefectures,with implying overgrazing rates of-32.2% and-29.7%,respectively.At the provincial level,without considering the carrying capacity with the use of supplementary forage,the overgrazing rate was found to be 53.85%,equivalent to 15.3× 106sheep units.When considering the supplementary forage,the overgrazing rate was 36.37%, about 11.7×106 sheep units.To that end,when the carrying capacity of natural grasslands or supplementary forage is compared with the actual number of livestock,the province tends to be overgrazed.