Nucleação como gatilho ecológico na restauração de áreas mineradas no Rio Grande do Sul

Abstract

The present study aimed to determine the effectiveness of nucleation techniques as an ecological restoration strategy in mined area, to determine the performance of these techniques as promoters of ecological triggers to initiate the processes of natural succession. Two nucleation techniques were evaluated: planting of native species in nuclei and brushwoods transposition, in a mining pit in Guaíba, RS. The nuclei were implanted in November 2014, when the seedlings were 12 months old, which were monitored semiannually until May 2017 when they were 42 months. The survival and growth rate of the dendrometric variables were evaluated. The brushwoods were implanted in August 2016 and monitored bimonthly until August 2017. The number of orders of fauna below, between and around the brushwoods was observed and recorded through non-destructive data collection method. Regarding planting in nuclei, the eight species analyzed had a survival rate above 80% at 42 months of age. Most species showed low growth, such as Bauhinia forficata, Casearia sylvestris, Cedrela fissilis, Cordia americana, Cupania vernalis and Parapiptadenia rigida, due to the limiting site and mechanical injuries caused by cattle. Schinus terebinthifolius and Mimosa bimucronata showed good development in relation to the analyzed variables. The species obtained a constant growth and were more adapted to the area. Mimosa bimucronata presented a significant growth in crown area, demonstrating nucleator character when aggregating herbaceous and shrub species below its broad crown. The nuclei, in general, were not efficient, but Mimosa bimucronata is a positive result of species that can serve as ecological trigger to drive succession in the area. In relation to the brushwood, 24 orders, among insects, arachnids, amphibians, reptiles, mollusks, oligochaetes and diplops, mostly belonging to the macro and mesofauna of the soil, were found. Anura, Araneae, Hymenoptera and Isóptera were the orders with the highest absolute frequency. There was an increase in the number of taxonomic units found at each survey, with a significant difference in the number of orders recorded per galleries from the fifth survey. In one year of monitoring, there was a gradual increase in the occurrence of groups of fauna associated with brushwood. These groups play important roles in soil restructuring and in the cycling of nutrients resulting from the decomposition of plant material, in addition to promoting the complexity of the food chains. Both techniques promoted ecological triggers for increased interactions and acceleration of the succession process, which has advanced in two and a half years since its implantation.