长江流域中上游植被NDVI时空变化及其地形分异效应

研究植被NDVI的时空演变及其地形分异效应,对于深入理解植被与人类活动的关系,揭示区域环境变迁,指导区域生态环境科学治理具有重要意义。以长江流域中上游作为研究区,基于1998～2015年SPOT-VEGETATION NDVI年度数据、DEM数据和基础地理信息数据,运用RS、GIS和数理统计分析等方法,探究了植被NDVI的时空演变特征及其地形分异效应,并对其影响原因进行了探讨。结果表明:(1)1998～2015年长江流域中上游地区生态环境得到极大改善,植被年均NDVI在时间上由1998年0.67增长至2015年0.75,年均增长率为0.57%。(2)植被NDVI在空间上的改善区域(48.58%)明显大于退化区域(11.1%),改善区域主要集中分布在研究区中东部地区。(3)植被NDVI在海拔500～1 000、1 000～1 500 m及坡度8°～15°、15°～25°区域改善趋势最大,在5 000 m和坡度0°～5°区域退化趋势最大;坡向对植被NDVI变化影响不显著。(4)18年间长江流域中上游地区植被NDVI变化可能是受天然林保护、退耕还林(草)等生态工程实施和人类社会经济活动共同作用的结果。该文能为长江流域中上游地区脆弱生态环境的治理和改善提供科学依据,进而筑牢长江中上游重要生态屏障,推进长江经济带绿色发展。

Temporal and Spatial Variation of Vegetation NDVI and Its Topographic Differentiation Effect in the Middle and Upper Reaches of the Yangtze River Basin

The study on the temporal and spatial evolution of vegetation NDVI and its topographic differentiation effect is of great significance for deeply understanding the relationship between vegetation and human activities, revealing the changes of regional environment and guiding the scientific governance of regional ecological environment. The upper and middle reaches of the Yangtze River Basin was chosen as study area. Based on yearly annual normalized difference vegetation index(NDVI) derived from SPOT sensor, DEM and basic geographical information, the temporal and spatial evolution characteristics and topographic differentiation effect of vegetation NDVI in the middle and upper reaches of the Yangtze River Basin are discussed, and the reasons for its influence are discussed. The results show that:① The ecological environment in the middle and upper reaches of the Yangtze River Basin has been greatly improved from 1998 to 2015. The average annual NDVI of vegetation increased from 0.67% in 1998 to 0.75% in 2015, with an average annual growth rate of 0.57%.② The spatial improvement area of vegetation NDVI (56.82%) was significantly larger than that of degraded area (7.3%), and the improvement area was mainly distributed in the middle and eastern part of the study area. ③ The improvement trend of vegetation NDVI was the highest in the area of 500~1 000 m, 1 000~1 500 m and slope of 8°~15°and 15°~25°, and the degradation trend was the highest in the area of >5 000 m and slope 0°~5 °, and the slope aspect had no significant effect on the change of vegetation NDVI. ④The change of vegetation NDVI in the middle and upper reaches of the Yangtze River Basin from 1998 to 2015 may be the result of the implementation of ecological projects such as natural forest protection, conversion of farmland to forest (grass) and human social and economic activities. ⑤This paper can provide a scientific basis for the treatment and improvement of the fragile ecological environment in the middle and upper reaches of the Yangtze River Basin, and then build an important ecological barrier in the middle and upper reaches of the Yangtze River, and promote the green development of the Yangtze River economic belt.