Studies on the composition, richness, and diversity of plant species in tropical communities are essential for understanding relevant ecological processes and for developing appropriate conservation policies. Considering that areas subject to direct impacts due to dam breach may in the long-term present changes in species composition and in soil parameters, we evaluated the composition of the flora, described the current vegetation profile, and evaluated whether differences in species composition was influenced by soil variables of three areas along the Gualaxo River, in Minas Gerais State, Brazil. In addition, we identified important plant species through occurrence and phytosociological parameters for ecological restoration projects in the affected region, serving as reference areas. We sampled plant species with DBH ≥ 5 cm (diameter at breast height – measured 1.30 m above ground level) in 77 plots distributed in three riparian forest areas. We calculated phytosociological parameters and related them to edaphic factors. A total of 1579 individual plants belonging to 53 botanical families and 227 species were sampled in the three areas. The Fabaceae family was the most representative with 46 species. Species composition and diversity among the sampled areas was similar and was associated with edaphic factors. Furthermore, some species (e.g. Xylopia sericea, Cupania emarginata and Ocotea pulchalla) showed an important relation with soil variables. Some species of the genera (e.g., Byrsonima, Xylopia, Ocotea, and Croton) and families (e.g., Fabaceae and Myrtaceae) found here, can be important species in the restauration process for the local and regional maintenance of floristic identity in the Rio Doce river.

We selected three areas of riparian forest (Seasonal Semideciduous Forest - Atlantic Forest) along the Gualaxo do Norte River, affluent of the Rio Doce River, in the Municipality of Mariana, MG for the vegetation sampling. The Gualaxo do Norte River was directly affected from the Samarco dam breach, as the ore tailings flow crossed the entire Gualaxo River until getting into the Rio Doce river. The plot method was used for vegetation characterization and sampling. The floristic and phytosociological survey of the adult stratum was carried out in 77 plots of 100 m2 (10 m × 10 m) established in three areas of Gualaxo do Norte River as follow: Águas Claras – AC (20° 17' 16.5" S and 43° 14' 59.0" W) with 28 plots, Antônio Pereira – AP (20° 16' 34.0" S and 43° 25' 50.0" W), with 24 plots, and Monsenhor Horta - MH (20° 20' 52.7" S and 43° 18' 42.7" W) with 25 plots, totalling 7700 m2. The individual's identification was carried out in the field, given prior species knowledge. Plant material was collected (vegetative or reproductive) for identification through specialized literature and existing material, and if not identified to the species level, were sent to specialists. Vouchers for all plant species were collected, identified, and deposited in the Montes Claros (MCMG) Herbarium, from Unimontes, and Universidade Federal de Minas Gerais (BHCB) Herbarium. The family names followed the Angiosperm Phylogeny Group (APG IV 2016), and species names were confirmed in the Plant list database (http://www.theplantlist.org/) and updated/corrected whenever necessary.

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