Large-scale forest restoration generates comprehensive biodiversity gains in an Amazonian mining site

Abstract

To reconcile environmental issues with socioeconomic development, the mitigation hierarchy emerges as a pivotal strategy that sequentially addresses environmental impacts through a structured approach of avoidance, minimization, remediation, and offsetting. No net loss (NNL) is achieved when biodiversity gains from all four mitigation stages are larger than the project's environmental impacts. Here, we assessed biodiversity changes linked to the implementation of the S11D Eliezer Batista iron mining Complex in the Carajás National Forest, Pará state, Brazil, expecting losses due to mining activities and gains through forest restoration offsets. We evaluated biodiversity stocks based on Biotic Value as the product of habitat importance and actual conditions. Habitat importance, a unique value for each class of land cover recognized within the study site, is based on the evaluation of habitat naturalness, rarity and endangerment, and substitutability. Actual conditions are computed from field-surveyed key ecological attributes of vegetation structure, community composition and diversity, and ecological processes, and forest restoration activities are able to restitute, within 4–6 years only, approximately 73 % of old-growth forest conditions. The Biotic Value ranges from 0 for mine lands to 1 for patchy savanna formations stocking above ironstone outcrops (locally known as cangas) and amounts to 0.43 units/ha for secondary forests. Between 2008 and 2021, we detected comprehensive land-use changes in the study area: Cangas, farmlands and old-growth forests decreased, while secondary forests and minelands increased considerably. Despite environmental degradation, the emergence of secondary forests contributed to a positive biodiversity balance within the areas managed by the mining company (+379 units), while biodiversity losses dominated outside the company's boundaries (−171 units). Although like-for-like compensation of canga impacts remains challenging, we thus conclude that forest restoration efforts initiated by the mining company effectively reversed the trajectory of environmental degradation prevailing in the landscape and provided considerable biodiversity gains for the region.