三峡库区1992-2012年森林景观格局演变研究

摘要

[目的]以三峡库区森林生态系统为研究对象,分析1992-2012年间森林景观格局演变过程,为森林景观恢复、森林资源可持续利用和景观格局优化提供基础研究.[方法]利用5期代表三峡工程不同建设阶段的遥感影像,揭示三峡库区森林景观格局的时、空演变过程,并从斑块面积分级和景观指数两个角度分析景观格局的破碎化过程.[结果]1992-2012年间,耕地和林地始终是三峡库区最主要景观类型,耕地大幅减少,森林面积与森林覆盖率逐年提升,森林景观结构比较稳定,呈现出针叶林＞灌木林＞针阔混交林＞落叶阔叶林＞常绿阔叶林的态势.森林分布不均,主要集中在库区库首和腹地西部,20年间森林景观格局空间变化呈“首尾平稳、腹地迅速增加”的趋势.森林景观斑块面积分级存在明显的两级分化,细碎斑块数量多面积小,100 hm2以上大斑块数量少面积大,但20年间两极分化的情况明显缓解,零星散布的森林斑块显著减少,集中连片的森林斑块数量增加且面积增大.20年间库区森林景观的平均斑块面积增加了54％,最大斑块指数提高了1.34倍,平均邻近指数提高了3.02倍,其中针叶林的景观优势度明显增加.[结论]库区生态建设与环境保护已初见成效,库区森林景观逐渐恢复,破碎化程度缓解,连通性提高,但在景观格局上仍分布不均:库首地区森林覆盖率高但以马尾松林居多、景观多样性欠佳,库尾都市区及长江沿线森林覆盖率还有待提高,地带性植被的比重应进一步提升.%[Objective] An analysis on the forest landscape pattern evolution in the Three Gorges Reservoir (TGR) area during 1992-2012 will contribute to forest landscape restoration,sustainable utilization of forest resources and landscape pattern optimization.[Method] Five time-series remote sensing images were selected to discover the changes of forest landscape in the TGR area.Two indexes (graduation statistics and landscape metrics) were included for this analysis.[Result] Cropland and forest were the dominant landscapes during 1992-2012,although cropland area reduced drastically,while forest area and forest coverage rate increased gradually.The structure of forest landscape was relatively stable.The forest was unevenly distributed with most concentrated in the east and center parts.In the past 20 years,the forest area increased rapidly in the central part,while kept steady in the east and west parts.The distribution of patch area shows obvious polarization,which means small fragmented patches were in large quantity while the large patches with areas above 100 hectares were in small quantity.But the polarization was obviously relieved in the past 20 years,the scattered forest patches were significantly reduced,the continuous patches were increased both in quantity and area.During the past 20 years,the mean patch size of forest landscape increased by 54％,while the largest patch index increased by 134％,and the mean proximity index increased by 302％.The landscape dominance of coniferous forest increased significantly.[Conclusion] With forest restoration,the fragmented patches were gradually connecting,the ecological condition was improved.However,the landscape pattern is spatially uneven distributed.The forest coverage rate is high in the east of the TGR area,but with poor landscape diversity dominated by Pinus massoniana.The forest coverage needs to be improved in the west of the TGR area and the zone along Yangtze River.