喀斯特山地土地利用变化的垂直分布特征

Vertical distribution of land use in karst mountainous region

  • 摘要: 喀斯特山区土地利用变化受复杂地形影响, 以往大尺度研究皆是对整个研究区地形特征进行统计, 局部土地利用变化空间特征和差异研究较少。本文以黔桂喀斯特山地为例, 构建土地利用动态垂直梯度指数, 刻画和揭示研究区土地利用变化的垂直分布特征。结果表明: 1990—2010年, 喀斯特山地土地利用的净变化面积较小, 但各土地利用类型的相互转化剧烈。耕地被建设用地挤占, 林地和草地又被开垦为耕地; 生态恢复工程使得林地、草地和水域等明显增加。增加和减少的耕地在垂直分布上明显错位, 减少耕地主要分布于低海拔(0~200 m)和缓坡度(0~5)区域, 而增加耕地主要位于高海拔(600~1 400 m)和陡坡(8~25)区域; 增加和减少的林地和草地在分布上相互对应, 分别在800~1 400 m和8~25出现峰值; 水域和建设用地的增加多位于低海拔(0~800 m)和缓坡度(0~5)区域。应用土地利用动态垂直梯度指数发现, 尽管2000—2010年研究区新增建设用地集中在最低海拔和最缓坡度等级, 但局部范围内新增建设用地趋近于相对更高海拔和陡坡区域分布。有限土地资源使得喀斯特山区有向高海拔、陡坡区域进行土地利用开发的趋势。土地利用动态垂直梯度指数, 既可进一步支撑采用全局统计分析方法结论, 也可分析和挖掘土地利用变化垂直分布特征的局部相对差异。

     

    Abstract: Complex terrain features affect the land use in the karst mountain regions. Vertical changes of land uses impact on their total qualities and utilization efficiencies. Characterizing the vertical distribution of land use change can guide the land use spatial management and optimization. The conventional methods were used to analyze the vertical distribution of the land use change for the entire study area in the large-scale analysis of previous studies, which may ignore the locally spatial information and discrimination. Taking the Guizhou and Guangxi karst mountainous region as the study area, the newly vertical gradient index of land use change, including the elevation gradient index and slope gradient index, were built and used to characterize and analyze the locally vertical distribution of land use change in the typical karst mountain. Results showed a relatively small net area of land use change, but a violently mutual conversion of various land use types in the study area from 1990 to 2010. Considerable arable lands were occupied by the expanded built-up lands, and the forests and grasslands were reclaimed to the arable land. Meanwhile, the forest, grassland and water body increased significantly because of the ecological restoration project. The conversion between the arable land, forest and grassland was the most intense. It showed a significant mismatch of the vertical distribution for the increased and decreased arable land. Decreased arable lands were primarily located in the region with the low altitude (0200 m) and gentle slope (05). In contrast, the increased arable lands were primarily located in the area with the high altitude (6001 400 m) and steep slope (825). It was a reciprocal relationship of vertical distribution between the increased and decreased forests and grassland, both types peaked at the altitude of 8001 400 m and the slope of 825. The increased water body and built-up land were primarily located in area with the low altitude (0800 m) and gentle slope (05). The vertical gradient index of land use change could quantify and visualize the local distribution and relative degree of land use change trend. Based on the vertical gradient index, most vertical distribution of land use change at local scale were found to be consistent to those at global scale, but also parts were different, which were not founded by the traditional methods. Although the newly expanded built-up land from 2000 to 2010 were mostly located in area of the lowest elevation and gentle slope class, they tended to be located in area with the relatively higher altitude and steeper slope compared to the originally vertical distribution at the local scale. Limited land resources leaded to the development of land uses approaching area with the relatively higher altitude and steeper slope in the Guizhou and Guangxi Karst Mountainous Region. The results demonstrated that the vertical gradient index of land use change might further support the results from the global statistical analysis, but also could analyze and explore the vertical distribution of land use change at the local scale, which was easily omitted by the traditional methods.

     

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