那曲地区草地植被时空格局与变化及其人文因素影响研究

Spatio-temporal pattern and change of Nagqu grassland and the influence of human factors

那曲草地作为西藏自治区畜牧业发展的重要基地,草地植被年际变化是自然因素和人类活动交互影响的结果。为了解决当地复杂的资源环境问题,需要深刻认清各种人文因素对草地影响的程度和机制。本研究利用2000-2009年的MODIS NDVI时间序列影像及相关统计资料,对那曲草地植被的空间和年际变化进行动态监测,并采用定性与定量相结合方式系统分析各个人文因素与草地植被格局和变化的关系。结果表明,1)那曲地区不同区域植被在2000-2009年表现出不同的年际变化趋势,在高大山脉高海拔的稀疏植被或冰雪覆盖周边区域,由于全球变暖且受人类活动影响较小而出现植被变好的状况,在人类活动强度较大的纯牧业县(那曲县、聂荣县和安多县)草地植被退化情况较为严重;2)分析那曲地区植被空间格局、年际变化分布图与道路网、居民点分布密度图在空间上具有较好的相关性,这也表明该研究区人类活动将直接影响目前良好的地表覆盖区域植被正常生长和繁育;3)以中心城镇那曲镇和109国道为代表,利用缓冲区分析方法研究发现距离人类活动越近的地区植被退化越严重,而统计资料显示那曲地区的人口、放牧强度、道路工程建设份额等指标都呈直线上升,将对草地植被生长构成严重的威胁,从而进一步影响那曲地区草地的理论承载力和经济可持续发展;4)此外,调查发现旅游和放牧的车辆碾压、矿产开采、采挖草药、安居工程建设、鼠患等因素对那曲草地都有一定程度的破坏。

Nagqu serves as an important and demonstration center of Tibetan stockbreeding development located in an extremely harsh natural environment with vulnerable ecosystems.In recent years,large areas of alpine grassland ecosystems of Northern Tibet have severely degraded and have been threatened by soil erosion,desertification,and human activities.The annual variation of vegetation is influenced by both natural conditions and human disturbances.To efficiently solve the complex resource-related and environmental issues,it is necessary to clarify how human factors affect the normal growth of rangeland vegetation.Various statistical analyses and time-series NDVI（normalized difference vegetation index） datasets from MODIS sensors between 2000 and 2009,were used to monitor the spatio-temporal variation of grassland.The relationships between grassland degradation and various human factors are discussed based on qualitative and quantitative systematic analysis.1） Due to snow melting related to global warming,the vegetation in some desertified and snow-covered regions of high altitude mountains showed an actively recovering trend,while the grasslands in purely livestock-breeding counties（such as Nagqu,Amdo and Nyainrong） of central Nagqu had some degenerative phenomenon;2） The spatial patterns of density maps of residential distribution and road network,vegetation NDVI image,and yearly variation map of vegetation NDVI showed similar spatial clustering characters,indicating that human activities directly influenced growth and reproduction of plants in flourishing vegetation cover;3） Taking Nagqu town and state highway No.109 as typical instances of human factors,the vegetation in regions closer to town centers or the road axis with more intense human disturbances showed more severe degradation.Further statistical analyses showed a linear upward trend for population,numbers of livestock and traffic-construction projects in Nagqu,which will bring serious threats to sustainable development of local pastures;4） Additionally,the grassland in Nagqu was also destroyed by grinding of tourists＇ and herders＇ vehicles,mining,digging herbal medicine,house-construction projects for low-income residents,and mice disasters.In order to protect the healthy development of Nagqu＇s rangelands and local economy,several feasible and constructive measures are proposed.