黄土高原森林破碎化的基本特征与时空格局演变

Spatiotemporal pattern of forest fragmentation in the Loess Plateau

为了评价黄土高原森林破碎化程度和退耕还林工程的成效,本文利用20世纪80年代以来7期(1980年、1990年、1995年、2000年、2005年、2008年和2015年)土地利用数据,采用森林破碎化模型分析了黄土高原35年的森林面积和森林破碎化程度的基本特征和时空格局,并在区域尺度及县级尺度分析了森林破碎化的变化规律和特征。结果表明:自20世纪80年代以来,黄土高原的森林面积比例呈现"先减后增"的变化特点;森林破碎化程度总体随时间呈现"先加剧后减缓"的演化特征;在空间格局上,森林破碎化呈现"斑块森林为主导,内部森林分布集中"的特点;在区域尺度上,水土流失较轻、自然条件较好的土石山区和河谷平原区的森林破碎化程度和区域生态环境改善更加明显;在县级尺度上,陕西和内蒙古的破碎化程度相对较大,山西的森林破碎化程度相对较低。总体来说,退耕还林工程实施以后,黄土高原森林面积显著提高,森林破碎化程度有效缓解,区域生态环境明显改善,在一定程度上对黄土高原生态恢复产生了积极的影响。

As the main type of terrestrial ecosystem, forests play an important role in maintaining biodiversity and regulating regional climates. However, increasingly aggravated deforestation or forest degradation, such as forest fragmentation, have impeded sustainable forest development and threatened biodiversity around the world, especially in the fragile Loess Plateau of China. Hence,the objective of this study was to investigate the spatiotemporal pattern of forest fragmentation in the Loess Plateau from 1980 to 2015 using a landscape fragmentation model and long-term land use datasets in seven periods（1980, 1990, 1995, 2000, 2005, 2008, and 2015） generated by the visual interpretation of Landsat images. We found that the fraction of forest area decreased first and then increased; meanwhile, the forest fragmentation situation aggravated first and then alleviated,corresponding with that of forest proportions. The highly fragmented patch forest category was predominant, while the least fragmented interior forest category was a minority and highly concentrated in its spatial distribution. In addition, the patch forest and interior forest categories decreased from 1980 to 1995, and then increased after 2000. At a regional level, forests in the plain valley areas and earth hill areas with limited soil erosion more easily recovered and showed a rapid recovery of forest fragmentation. At the county level, forest fragmentation differed remarkably in various counties; specifically, forest fragmentation problems in Shaanxi and Inner Mongolia provinces were more severe than in Shanxi province. On the whole, before the implementation of the＂Grain for Green＂Project, the areas of forests tended to decline and forest fragmentation was aggravated, severely damaging the regional environment. After the implementation of the＂Grain for Green＂Project, areas of forests increased rapidly and forest fragmentation was alleviated.