Variability of environmental factors and the effects on vegetation diversity with different restoration years in a large open-pit phosphorite mine

Open-pit mining activities can cause serious disturbance to the local land and even regional vegetation communities. Vegetation restoration is a crucial approach for maintaining ecological stability in a post-mining area. In this study, the role of the environment factors on vegetation diversity under different restoration years (2a, 5a, 10a and control area) in the largest phosphate mining areas in Southwestern China was evaluated by a multi-model inference (MMI) based on the Akaike information criterion (AIC). Three competing models of environmental factors included vegetation nutrient content (M1), soil heavy metal content (M2) and human disturbance (M3) were constructed to analyze how they impact vegetation diversity. The results revealed the changing effects of different environmental factors under four restoration stages. Heavy metal content in the soil (M2) had the strongest effect on vegetation diversity in the restoration areas at 2 and 10 years, whereas human disturbance (M3) had the strongest effect in the restoration area at 5 years. In the control area, the vegetation nutrient content (M1) had the strongest effect on vegetation diversity. According to the different models, a comprehensive index of environmental factors (CIEF) was established to build the fitting formula with vegetation diversity. The index could be used for assessing the efficiency of vegetation restoration by comparing the theoretical value and the actual value of Shannon's diversity index in the study area and other phosphate mining areas.