基于MODIS-EVI评估三江源高寒草地的保护成效

Conservation outcomes assessment of Sanjiangyuan alpine grassland with MODIS-EVI approach

三江源是我国生态保护的优先区域。自2005年以来,国家投入大量资金在三江源实施了一系列生态保护措施和工程,主要目的之一是保护和恢复草地生态系统。本文基于中分辨率成像光谱仪(MODIS)增强型植被指数(EVI)数据和野外实测样方,从草地生物量的角度评估了三江源工程的保护成效,以期为后续的保护措施提供参考。本文使用2000–2016年间在青藏高原248个样地的实测地上生物量数据和同期的EVI数据,比较了通过EVI估算草地地上生物量的不同建模方法,并从中选择表现最佳的乘幂模型反演了三江源高寒草地的地上生物量,用趋势分析法得出了生物量的变化。结果显示,2000–2016年间,三江源高寒草地地上生物量没有发生显著变化的面积占62%,显著增加的地方主要在西部和北部,占22%,显著减少的地方则主要在中部和南部,占16%;2000–2016年间,草地地上生物量的年际波动较大,但总趋势不显著;在2012年后,地上生物量表现出显著降低的趋势。三江源国家级自然保护区外部的草地地上生物量高于内部,使用匹配法比较保护区内外草地地上生物量变化的情况,结果发现在生态保护工程实施的2005–2012年间,三江源保护区内的草地生物量没有显著增加。

The Sanjiangyuan Region is a priority area for ecosystem conservation in China. Since 2005, the government has contributed significant funding to implement ecological conservation and restoration to protect and restore the grasslands. This study correlated aboveground biomass（AGB） data from 248 sites scattered across the Sanjiangyuan Region with MODIS Enhanced Vegetation Index（EVI） data from 2000 to 2016 and utilized four regression models to estimate AGB by EVI. Results showed that power-function model worked best for grasslands in the Sanjiangyuan Region. Trend analysis showed no significant trends in 62% of the area of Sanjiangyuan, with 22% of the area, mainly distributed in the western and northern regions, increasing significantly and 16% of the area, sporadically located in the central and southern regions, decreasing significantly from 2000 to 2016. In general, the AGB of the entire area showed no significant increases or decreases with high annual fluctuations since 2000. However, there have been significant decreases since 2012. The AGB inside of the Sanjiangyuan Nature Reserve was lower than that found outside, and didn＇t increase significantly during first-stage projects between 2005 and 2012, based on results from matching methods.