Ecosystem restoration after bauxite mining: favorable indicators for Technosols construction and soil management using liming and subsoiling

Although its economic importance, bauxite mining causes the loss of natural ecosystems. In this sense, the Technosols building from materials made or modified by man, such as mine tailings, is necessary for recovering degraded areas. Additionally, the Technosols management, such as subsoiling and liming, increases chances of plants establishment and growth. In this study, a degraded area by bauxite mining with constructed Technosol in the Eastern Amazon, Brazil, was tested under three different soil management treatments: Technosol-1 (Tech-1), Liming only; Technosol-2 (Tech-2), Subsoiling + 200 g of NPK in the pit; Technosol-3 (Tech-3), Scarification + liming + all Tech-2 procedures. In every treatment and in a reference forest (R-forest), 8 years after the initial seedling planting, three types of indicators were assessed: structural (horizontal vegetation structure, density of natural regeneration, and soil cover), compositional (species diversity, ecological groups, and dispersal syndromes), and functional (chemical properties of Technosols and dry matter and nutrients from the litter stock). The most representative species in all treatments were Croton matourensis and Vismia guianensis, both coming from the natural regeneration and common in early successional stages. Coverage rates in all treatments showed less than 5% of exposed Technosol and the diversity, ecological group, and dispersal syndrome indexes followed a successful trajectory along 8 years. Tech-2 and Tech-3 presented the best chemical attributes and nutrients in the litter stock, but they would probably last several decades to reach the R-forest attributes. Thus, subsoiling alone or with liming provided the best chemical results for soil, litter, and vegetation performance, being recommended to speed up restoration of degrades areas by bauxite mining in the Amazon.