漫湾库区景观破碎化对区域生境质量的影响

Assessment of the influences of landscape fragmentation on regional habitat quality in the Manwan Basin

水利工程的建设不仅改变了库区的景观格局,还会导致区域生物生境质量的变化。以澜沧江漫湾库区为例,在综合海拔高度、植被类型和水源地距离生境因子的基础上,考虑生物扩散过程,研究了建坝前后整个库区以及典型研究小区(库首、库中、库尾、对照)的重要生境斑块空间分布变化。结果表明:漫湾水电站建成后库区的猕猴总体生境破碎化程度增加,景观连接度减少且重要生境斑块的比例也有所降低,生境质量整体下降;4个研究小区的景观格局变化情况同整个库区相一致。空间上,生境质量明显退化的地区主要分布在库区的西部和南部,尤其是库尾地区,其生境斑块数量相较于建坝前增长了9倍,而景观连接度指数下降了81.48%。回归分析结果表明景观连接度指数与占景观面积百分比指数(PLAND)呈显著正相关(R^2=0.973),与斑块数(NP)呈显著负相关(R^2=-0.611);肯德尔系数表明斑块数(NP)、最大斑块指数(LPI)、占景观百分比指数(PLAND)、相似邻近百分比指数(PLADJ)、连通度指数(CONNECT)和香农多样性指数(SHDI)7个景观格局指数与景观连接度指数均表现出显著一致性。由此看出,库区景观破碎化越严重、区域景观连接度越低生境质量退化越明显;而提高生境主要植被类型的覆盖率、保护连接度贡献大的重要斑块和建设生态廊道,可以有效恢复库区生物生境质量。

Dam construction and the subsequent land use change have obvious impacts on regional ecosystems. Not only the landscape pattern, but also the regional habitat quality are affected by these human activities. Taking the Manwan Basin of the Lancang River as a ease study, habitat quality changes and key patch distributions of the whole study area and four substudy areas （reservoir head zone, reservoir center zone, reservoir trail zone, and control zone ） before and after dam construction were determined based on remote sensing images and GIS techniques, considering multiple factors （elevation, land use, and distance from water） and the dispersal ability of the focused species. The probability of connectivity index （PC） was a proxy for habitat quality in this study. Dispersal distances were set at 100, 300, 500, 700 m and 1000 m to calculate the PC index, which was further used to identify the importance level of habitat patches. The results showed that the degree of habitat fragmentation for macaques increased in the Manwan Basin, while the landscape connectivity between habitat patches and the percentage of key patches decreased after the construction of the Manwan hydropower plant. Regional habitat quality clearly declined, and the change in landscape pattern indicators in the four sub-study areas was similar to that in the total Manwan Basin. The PC index clearly decreased over time by about 55.51% on average, and there were 317.2 km^2 of high-level patches converted to much lower levels from 1974 to 1991, while there were slight declines in the hydropower operation period. Habitat degradation occurred mainly in the south and west regions, especially in the reservoir tail zone, where patch number increased nine-fold while the landscape connectivity decreased by 81.48%. A linear- regression analysis indicated that the landscape connectivity index was positively associated with the percentage of landscape area index （R^2= 0.9729）, but had a negative correlation with the patch number index （R^2= -0.6106） ; Kendall＇s tau-b （ τb ） coefficient indicated that, except for the total edge index （ TE）, all of the other landscape pattern indicators （ number of patches （ NP ）, largest patch index （ LPI）, percentage of landscape index （ PLAND）, percentage of like adjacencies （PLADJ）, connectance （CONNECT）, and Shannon＇s diversity index （SHDI）） showed a remarkable correlation with landscape connectivity. It can be seen that the more serious the landscape fragmentation was, the more landscape connectivity and habitat quality were reduced. The percent increase in the dominant vegetation cover of habitats, which caused the PLAND to increase, can be an effective measure to restore the habitat quality. In addition, the protection of key patches and the construction of an ecological corridor, which would enhance the landscape connectivity, would contribute to the habitat quality recovery and the maintenance of landscape ecological functions.