Interaction mechanism between floristic quality and environmental factors during ecological restoration in a mine area based on structural equation modeling

Open-pit mining activities cause great damage to the local ecosystems. It is therefore necessary to assess and recover the vegetation status to maintain ecological stability. In this study, the Floristic Quality Index (FQI) was used to assess the vegetation habitat and the structural equation model (SEM) was applied to quantify the influences of different environmental factors on FQI in the Kunyang open-pit phosphate rock mine in Yunnan Province, China. Non-metric multidimensional scaling analyses revealed that great differences of vegetation community composition existed in the sampled plots, even those at similar distances to mining areas, which indicates that disturbing distance was not the only factor to determine the vegetation community. SEM results showed that Cu promoted the FQI most obviously (0.84), followed by Co (0.75), while the inhibition of Cd content in soil to the FQI was the most significant (-0.88), followed by TK (-0.82), and C (-0.79). Soil fertility quality and soil pollution indexes were also established to analyze the effects of comprehensive soil parameters on FQI. The results showed that the soil fertility quality index had a strong negative effect on FQI, which revealed that higher levels of TP, TN, TK, and other nutrients in the soil would produce 'toxicity' to the growth of vegetation. Findings from our study could provide a scientific method for assessing the ecological restoration results in the mining area.