Vertical distribution of land use in karst mountainous region

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.