Multifunctional soil recovery during the restoration of Brazil's Atlantic forest after bauxite mining.
Ecosystem restoration is a global priority, currently promoted by several ambitious commitments. Most of the research to guide restoration practices was so far put on the recovery of above-ground functions and services, although soil health is increasingly recognized as a fundamental condition to restoration success. Soil restoration is particularly needed in mining areas, in which the surface soil layers are removed and the left over, highly deprived substrate does not support vegetation recovery. Here, we evaluated the potential of active restoration to recover soil attributes after bauxite mining in the Brazil's Atlantic Forest. We specifically studied how physical, chemical and microbiological soil attributes down to 40 cm depth respond to restoration (i.e. topsoil spreading and tree planting) by comparing newly mined areas, areas undergoing restoration for ~7 years and conserved forests. We further explored the associations between microbiological and physico-chemical soil attributes. Restoration interventions resulted in a 10-fold increase in the soil organic matter content compared to mined areas, as well as in the recovery of P content. Restoration was also shown to be associated with the recovery of the activity and diversity of soil bacterial communities, reaching similar levels to those observed in conserved forest. Restored and conserved forests were characterized by a higher proportion of Acidobacteria, Planctomycetes and Verrucomicrobia. All bacterial attributes were correlated with soil physical attributes, except for microporosity, and with organic matter and cation exchange capacity. Within a few years, restoration allowed recovering crucial physical, chemical and microbiological soil attributes, reaching levels comparable to those found in conserved forests. Synthesis and applications. We demonstrate that intensive management can result in the fast restoration of tropical forest soils after mining, at least at small scales. Our results stress the need to consider soil recovery both as a driver and a measure of ecosystem restoration success, and support the development of more holistic monitoring protocols to be used during the United Nations Decade on Ecosystem Restoration.