西藏生态安全屏障保护与建设工程的宏观生态效应

西藏高原是我国重要的生态屏障、江河源区与生物物种基因库,为了保障其生态功能的持续有效发挥,2008年开始实施西藏高原生态安全屏障保护与建设工程。论文基于工程规划目标,通过对比监测2000—2008年与2008—2015年西藏高原生态系统及其关键服务的时空变化,科学地评估西藏高原生态工程的生态效应。结果表明：工程实施前、后8 a相比,1）西藏高原生态系统格局稳定少动,生态系统宏观状况趋向良性发展。森林面积持续增加,荒漠面积显著减少,水体与湿地面积从减少转变为增加。2）草地退化趋势明显减弱、草地恢复态势显著,退化草地占比下降了19.9%,恢复草地占比增加了33%。植被覆盖度增加趋势明显,平均提高了1.9%,特别是高寒草甸类。草地载畜压力明显减少,牧草供给能力提升,草畜矛盾有所缓解。3）生态系统水源涵养能力增加,碳汇总量略有提高,防风固沙服务能力稳步上升。然而,降雨量增加导致降雨侵蚀力增强,植被覆盖度增加但植被根系土壤层无法短时期内恢复,从而导致土壤保持服务能力有所下降。4）西藏高原的暖湿化气候有利于减缓荒漠化进程并促进生态系统恢复,而生态安全屏障保护与建设工程的实施对西藏高原生态系统服务能力的提升特别是工程区局部生态恢复具有一定的正面作用。

The Ecological Effects of Ecological Security Barrier Protection and Construction Project in Tibet Plateau

Tibet Plateau is an important ecological barrier of China. It is also the source region of many rivers and the gene bank of biological species. In order to protect the ecological function of Tibet Plateau, Ecological Security Barrier Protection and Construction Project was carried out in Tibet Plateau since 2008. Based on the objective of the project, this paper assessed the ecological effects of the Ecological Security Barrier Protection and Construction Project scientifically by comparing and monitoring the temporal and spatial changes of ecosystem and its key services between 2000-2008 and 2008-2015 in Tibet Plateau. Comparing the ecosystem in eight years before and eight years after the project, it was concluded that: 1) The ecosystem structure of the Tibet Plateau was stable and less dynamic, and the macro patterns of the ecosystem tended better. The area of forest continued to increase, the desert was significantly reduced, and the area of water and wetland decreased firstly and then increased. 2) The trend of grassland degradation was weakened, and the grassland was obviously restored. The proportion of degrading grassland decreased by 19.9% and the proportion of restored grassland increased by 33%. The vegetation coverage increased 1.9% in Tibet Plateau, especially the alpine meadow. The significantly reduced loading pressure of grassland and the enhanced forage supply capacity both alleviated the contradiction between grassland and livestock. 3) The capacity of ecosystem water conservation increased, the total amount of carbon sinks increased slightly, and the capacity of ecosystem sand fixation increased steadily. However, the increasing rainfall enhanced the erosion, so soil layer could not recover in a short period in spite of the increase of vegetation coverage. Thus, the capacity of soil conservation service declined. 4) The warm and humid climate in the Tibet Plateau is conducive to slow down the process of desertification and promote the ecosystem restoration, and the implementation of the Ecological Security Barrier Protection and Construction Project has positive effects on the improvement of the ecosystem service capacity, especially in the local regions of the project.