Analysis of spatio-temporal evolution and driving factors of vegetation fraction for opencast coal mine in grassland area

Abstract: Based on Landsat TM satellite remote sensing image data, the paper utilized the vegetation index and vegetation fraction to analyze their spatio-temporal evolution and its driving factors. Spatial heterogeneity and its driving mechanism of vegetation fraction were analyzed under the linkage of mining and reclamation. Based on regression coefficient, standard deviation, gradation conversion matrix, and so on, we revealed the response of the vegetation cover to the mining and reclamation activities with time through the analyses of the trend and fluctuation of vegetation coverage in the study area, the mining area and the reclamation area. The results showed that the vegetation fraction and its grade in different years had some similarity, and the pattern of spatio-temporal evolution was broken by mining and reclamation activities in open pit mines to some extent. The vegetation coverage in the study area was mainly the middle (Grade IV) and the middle-low (Grade III) level, and according to the average of many years, both of them accounted for more than 80% of the total area of the study area. The ratio of the area with increased vegetation cover degree to the area with decreased vegetation cover degree was 2:3, and correlation coefficient was between ?0.9266 and 0.4805. The correlation was not significant in the range of positive value, but was significant in the negative part. Correlation coefficient from ?0.9266 to ?0.895 was through the significance test of 0.025, and vegetation damage was the most severe, which belonged to a very significant change, and almost all were distributed in the exploited Xi'er, Xiyi and Dong'er open-pit stope and their solid waste yard, industrial sites and road with an area of about 4.85 km2. The standard deviation (SD) of inter-annual vegetation fraction for the study area was in 0-0.49. The vegetation fraction of open pit area, dump and surrounding areas with a range of 1.5 km was significantly decreased, and had gradually converged. Reclamation revegetation would experience a "high-low-high" cycle in the study area, and according to the changes of vegetation reclamation, protection period must ensure more than 6 years in semiarid grassland. In the study area, the land reclamation standard was higher than the surrounding area, and the recovery effect was better. More than 70% of areas had the transition of vegetation fraction, and the transition was relatively frequent. The fluctuation degree for the area of Grade III and II was the largest, which were the most damaged. There was 90 percent of the area of GradeⅠwhich was transferred by the mining activities. To enhance the vegetation coverage in the study area, it was required to reduce the social pressure and improve the ecological resilience. To reduce social pressure, we should consider the coal mining and solid waste stacking technology, with minimal impact on the ecological process in the form of a layered, limited mining area and stope arrangement for solid waste. The improvement of ecological resilience should increase the input of land reclamation, and steadily improve the coefficient of vegetation restoration in the mining area. The research results will provide information support for the ecological environmental protection and decision making, restoration and management in the area of open pit coal mine.