西藏地区草地承载力及其时空变化

Carrying capacity of grasslands and its spatiotemporal change in Tibet, China

在不适合和不能放牧区域划定、满足生态保护需要的牧草生物量估算、草地生产能力修正等的基础上,开展西藏地区县域草地承载力及其时空变化研究,分析农业、林业等补饲对草地承载力的影响机制,以及草地承载力与草地生态状况变化的相互关系.结果表明:(1)西藏地区县域草地载畜量和补饲载畜量呈显著的地域差异,主要影响因素分别为水分条件和热量因素;(2)2011年藏东南、藏西北部分县域草地资源仍有盈余,但是全区及其多数县域草地生态系统处于超载状态且自2000年以来不断加剧,草地承载状况及其动态变化的空间自相关性下降、空间异质性增强;(3)牲畜存栏量增长过快、草地资源供需空间匹配不协调是造成草地超载且不断加剧的主要原因;(4)通过缓解草地资源供需的不平衡性和不协调性,农业、林业等补饲可以改善全区尤其是农业县、半农半牧县草地承载状况,但对草地承载状况变化趋势的影响有限;(5)县域草地生态状况的下降趋势与其草地超载、草地承载率下降具有较强的相关性.因此,适合放牧区域划定、牲畜存栏量控制和畜牧业布局优化是改善西藏地区草地承载状况、减缓其草地生态状况下降趋势的主要途径.

The carrying capacity of grassland and the carrying capacity of grassland with supplementary feeding were analyzed in Tibet, China. This analysis was based on identifying areas unsuitable for grazing or where grazing was not possible, correcting grass yield and calculating the demand for grass used for ecological protection, estimating the carrying capacity of grasslands at the county level. Also, the spatiotemporal change in the carrying capacity of grasslands over time, the effects of supplementary feeding of livestock on agricultural and forestry land on the trends and dynamics of the carrying capacity of grasslands, and the relationship between the carrying ratio of grasslands and the ecological status of counties were explored. Results showed that there was a significant regional difference in the spatial distribution of the carrying capacity of grasslands and the carrying capacity of grasslands with supplementary feeding of livestock in Tibet; these differences depended on water conditions and temperature, respectively. Although some counties in Southeast and Northwest Tibet had a grass surplus in 2011, grassland ecosystems of most counties and in Tibet as a whole were overstocked with livestock, shortages of adequate forage have become more serious since 2000. Furthermore, while the spatial autocorrelation of the carrying status of grasslands and its dynamic changes decreased, the spatial heterogeneity of the carrying status of grasslands increased. These characteristics were mainly the result of a rapid expansion of the stocking levels for livestock, and the spatial mismatch between the demand and supply of grass resources. By mitigating the quantitative and spatial mismatch between supply and demand for grass resources, the use of supplemental feeding on agricultural and forestry lands could improve the grassland carrying capacity of Tibet as a whole, especially for agricultural and semi-agricultural counties. However, such mitigation had a less significant effect on the dynamic trends of the carrying capacity of grasslands. In addition, the decreasing trend of the ecological quality in the counties was significantly correlated with the overstocking of grasslands with grazing animals and the decrease in the carrying ratio of grasslands in Tibet. Therefore, the main measures that are needed to improve the carrying capacity of grasslands and to mitigate the decreasing trend of the ecological quality of grasslands will include zoning areas suitable for grazing, controlling the stocking levels of livestock and optimizing the distribution of animal husbandry.