Minimum thresholds of key ecological attributes facilitate the tracking of mineland restoration

Abstract

The restitution of biodiversity and ecosystem services to premining levels requires long time periods. This paper proposes quantifiable criteria to classify minelands as minimally restored compatible with (pluri)annual corporate budget cycles, reducing the probability of the need for future interventions. For that, we reviewed the scientific literature for key ecological attributes and outlined time frames necessary for compliance with these criteria based on iron mines from Brazil. For minimum restoration, principal soil functions should be initially reestablished and the vegetation cover should be dominated by native zoochoric and animal-pollinated plant species to guarantee connectivity with neighboring areas. Furthermore, areas should be free from the risk of future degradation, and minimum ecosystem functions such as photosynthesis, atmospheric nitrogen fixation, and litter formation should take place in these sites. In accordance with the available literature, we propose response ratios larger than 20% compared to restoration targets for all quantitative environmental indicators to qualify an area as minimally restored. Data from real-world cases show that these criteria can be met in iron minelands after short periods of restoration. Thus, the definition of interim results of the restoration process enables to cope with corporate budget cycles. However, further studies are necessary to outline how minimum restoration standards can be defined for further ores or tailings, and whether compliance with minimum restoration standards in fact promotes successional processes and further development toward restoration targets.