Controversies and hidden risks in biodiversity offsets in critically threatened Canga (ironstone) ecosystems in Brazil

Canga, or ironstone, ecosystems are hotspots of old-growth plant diversity and highly specialized cave invertebrates. These ancient metalliferous habitats are amongst the most threatened ecosystems because of the destruction caused by large-scale iron ore mining. International debate on biodiversity offsets is increasing because these mechanisms are seen as tools for potentially balancing economic development with conservation biodiversity. Leading mining companies worldwide, including some of the largest iron ore producers in Brazil, are signatories to offset principles and best practices that aim to achieve no net loss of habitats, species or ecosystem functions. We aimed to analyse whether Brazilian legal requirements for biodiversity offsets result in the achievement of conservation outcomes or in elevated threat of extinction in canga ecosystems. We evaluated technical reports that support decision-making related to environmental licensing for iron ore mining and specific offset proposals linked to the Atlantic Forest Act. We found a relevant net loss in canga ecosystems and observed shortcomings related to the equivalency and transparency of offset principles. These deficiencies are mainly related to lax norms and regulations and the absence of an integrated database for accessing information on environmental licensing processes. We argue that both policy flaws and low engagement by the Brazilian mining industry in implementing offset principles have increased the threat of extinction in canga ecosystems.