Monitoring of non-photosynthetic vegetation coverage changes in arid and semi-arid mining areas based on linear spectral decomposition

Non-photosynthetic vegetation cover plays a crucial role in increasing soil fertility and mitigating wind and water erosion in mining areas. It is an important indicator for evaluating land reclamation and ecological restoration in mining areas, but effective monitoring methods remain lacking. This paper uses Sentinel satellite imagery as the data source and employs the NDVI-DFI pixel triad model and the LIM linear index model to estimate non-photosynthetic vegetation coverage in mining areas. The paper also analyzes the variation patterns of non-photosynthetic vegetation under different seasons, regions, and reclamation models. The results show that: ① the NDVI-DFI feature spaces of the Heidaigou Open-pit Coal Mine and the Haerwusu Open-pit Coal Mine of Zhunneng Group are triangular, which conforms to the basic assumption of the pixel triad model. ② Compared with the NDVI-DFI pixel triad model, the LIM linear index model significantly reduces the root mean square error in the inversion of non-photosynthetic vegetation coverage, with R² reaching 0.892 3. ③ The seasonal variation characteristics of non-photosynthetic vegetation coverage in the study area are obvious and form a reciprocal relationship with photosynthetic vegetation coverage. In stripped and mining areas, there is no vegetation throughout the year; spoil areas have a small amount of both non-photosynthetic and photosynthetic vegetation; in reclaimed areas, non-photosynthetic vegetation and bare soil dominate in winter and spring, accounting for 46% and 45% respectively, while in summer, photosynthetic vegetation coverage exceeds 78%. Compared with the surrounding control areas, the non-photosynthetic vegetation in regions with shorter reclamation periods fluctuates more strongly with the seasons. ④ There are significant differences in the composition and seasonal variation of vegetation coverage under different reclamation modes. Evergreen conifer forests have the most stable vegetation coverage, with photosynthetic vegetation coverage greater than 85% in all four seasons, while 90% of the photosynthetic vegetation in deciduous broadleaf forests, mixed conifer-broadleaf forests, shrubs, and grasslands declines in winter and transforms into non-photosynthetic vegetation or bare soil. In winter and spring, bare soil coverage increases by 23%-42% compared with summer. Future attention should be paid to the monitoring and analysis of non-photosynthetic vegetation in winter and spring to provide a basis for optimizing and managing reclaimed vegetation.