甘肃白龙江流域植被覆盖度及景观格局变化

基于1998—2012年SPOT NDVI数据，采用像元二分模型和景观格局分析方法，对甘肃白龙江流域植被覆盖度及景观格局时空变化及影响因素进行分析。结果表明:（1）1998—2012年白龙江流域植被覆盖度明显增加，高植被覆盖度面积增加量最大（737.30 km²），2012年中高和高植被覆盖度面积比例达70.7%，植被覆盖度增加区域主要分布在宕昌县北部、岷江东岸、舟曲—武都段白龙江两岸及其以北区域。（2）研究期间，白龙江流域植被覆盖整体改善、局地退化，植被覆盖度显著增加和轻度增加的总面积和比例分别为4 675.90 km²，25%，显著减少的面积仅占3.84%。（3）1998—2012年景观破碎度增大，斑块密度增加了58.23%；景观形状趋于复杂化，LSI，AWMPFD和IJI分别增大到25.14，1.128，80.01；香农多样性和均匀度指数分别减少到1.342，0.834。（4）白龙江流域植被覆盖度增加是自然因素和人为因素共同作用的结果，退耕还林、天然林保护等一系列生态工程的实施是植被覆盖度增加的主要原因。

Dynamic Variations of Vegetation Coverage and Landscape Pattern in Bailongjiang Basin of Southern Gansu

Based on the SPOT NDVI during the period 1998—2012, this paper analyzes the fractional vegetation coverage temporal-spatial variation and landscape pattern in Bailongjiang Basin of southern Gansu by using the methods of dimidiate pixel model and landscape pattern analysis. Results are shown as the following: (1) from 1998 to 2012, fractional vegetation coverage of the study area increased, the area of high vegetation coverage increased apparently (about 737.30 km²), the ratio of high vegetation coverage to intermediate vegetation coverage was 70.7%, and the increased region mainly distributed in the northern Tanchang, the eastern riverside of Minjiang River, both sides of Bailongjiang River from Zhouqu to Wudu and north of it; (2) though the vegetation coverage presented an overall increase, it locally degraded in some areas, during that period, the areas and ratio of obviously increased region to slightly increased region were 4 675.90 km², 25%, respectively, and the ratio of obviously decreased region only accounted for 3.84%; (3) from 1998 to 2012, the landscape fragmentation increased, with patch density increased by 58.23%; landscape shape was prone to be more complicated; LSI, AWMPFD, and IJI increased to 25.14, 1.128, and 80.01, respectively. In addition, SHDI and SHEI reduced to 1.342 and 0.834, respectively. (4) the improvement of the fractional vegetation coverage in Bailongjiang Basin was the interactive effect of natural factors and human activities, but the main cause was the implementation of the series of ecological projects, such as ‘Grain for Green Project’ and ‘Natural Forest Protection’.