Abstract:
Mining rare earth ore has brought vegetation degradation, serious ecological and environmental problems in mining area, and it has already received more and more attentions and concerns by the society. By using 23 years Landsat series remote sensing images as data source, and choosing Lingbei rare earth mining area in Dingnan County as study area, in this paper, we analyzed the change of vegetation coverage of landscape pattern under the disturbance of rare earth mining. In order to improve the reliability of analyzing landscape pattern, the vegetation coverage of study area was extracted with four methods of forest canopy density mapping model(FCD), dimidiate pixel model(DPM), three-endmember and four-endmember linear spectral mixture model(LSMM). Taking vegetation coverage of the studied area acquired from the high-spatial-resolution remote sensing image of Pleiades as the checking data, the most suitable method of vegetation coverage in rare earth mining area was selected. And the change of landscape pattern was analyzed with this method. In addition, to prove the universality of this method, vegetation coverage of Heling rare earth mining area in Xunwu County was also extracted with methods of FCD model, DPM and three-endmember LSMM. In the test, we selected randomly 30 samples from a 0.5 meter high-spatial-resolution aerial image as the checking data. The result showed that the correlation coefficients of FCD model, DPM, three-endmember and four-endmember LSMM were 0.900 8, 0.924 7, 0.980 4 and 0.946 5, respectively. The Root Mean Square Error(RMSE) of FCD model, DPM, three-endmember and four-endmember LSMM were 0.341 1, 0.243 4, 0.037 8 and 0.089 3, respectivley. Similar results were obtained from the Heling rare earth mining area in Xunwu County. These two parameters of the correlation coefficients and RMSE could clearly show that the three-endmember LSMM was more suitable and accuracy for the extraction of vegetation coverage due to considering the spectral characteristics of peculiar tail sand in rare earth mining area. The landscape pattern dynamic analysis showed that fragmentation of low-level vegetation coverage and high-level vegetation coverage was at the low level in the mining area, concentrated and connected trend was obvious. And patch density(PD) value of the other three levels′ vegetation coverage were higher, they existed some ecological risks. The Largest Patch Index(LPI) of low-level vegetation coverage was relatively large in four years, and showed the fluctuating change. The area was mainly constituted by the bare of rare occurrences, and it had close relationship between ore occurrences′ reclamation and expanding. When LPI reached 0.543 6 and its area was 1 km2 in 2013, vegetation destruction caused by an individual mine was still larger. When the LPI of high-level vegetation coverage had a more dramatic change, and it reached the maximum of 80.519 0 in 2008, the area of high-level vegetation coverage increased in patches of ways due to people strengthened on ecological governance of rare earth mining area. When around small patches of low-level vegetation coverage gradually transformed into high-level vegetation coverage, high-level vegetation coverage patches became the entire mining matrix patches. The Aggregation Index(AI) of low-level vegetation coverage was consistently high, and its LPI was lower than high-level vegetation coverage. When the ionic rare earth was mined mainly in individual occurrence of small area, and ore occurrences were many and dispersed, this led environmental damage that were more difficult to control. After year 1999, with the scale expansion of mining and its process improvement, rare earth mining became the main cause for mining area′s landscape change. On the premise of overall improvement of ecological environment in mining area, the low-level vegetation coverage area concentrated in the ore occurrences and surrounding ore occurrences become landscape distribution pattern with rare earth mining area features of ore occurrences.