Since the 1970s, Mineração Rio do Norte - MRN has been mining bauxite in the Saracá-Taquera National Forest, located in Porto Trombetas, Oriximiná (PA). After the mining process, the modified forest landscape is restored, through reforestation with native Amazonian tree species. One of the projects adopted by MRN, aiming at the restoration of this landscape, is the Project of Environmental Monitoring through the installation of permanent plots, which among others, has the objective of annually monitoring the forest plantations developed by the company since 1981. Within this study is included the study of the natural regeneration of tree species in the respective reforestations. In the present work we analyze the floristic composition, phytosociology and structure of the natural regeneration of the trees in these reforestations promoted by MRN, from 1981 to 1987 and 1992 to 1996. In the reforestations of each year two permanent plots (25x10m) were planted, and the specific study of natural regeneration began in 2001. A total of 1778 individuals were recorded, distributed among 142 species and 34 families. The families with the highest species richness were Mimosaceae (17 species), Annonaceae (13), Fabaceae (11), Caesalpiniaceae (10) and Melastomataceae (9); nine families had a single species. The highest abundances were observed in Guttiferae (506 individuals), Melastomataceae (308), Flacourtiaceae (190), Mimosaceae (137), Euphorbiaceae (115) and Celastraceae (100). Combretaceae and Sapotaceae showed only one individual, consequently only one species. The species with the highest abundance were Vismia Iatifolia (323 individuals), Beliucia grossularoides (234), Laetia proera and Vismia cayenensis (175), Miconia gratissima (109) and Goupia glabra (100); 45 species (or 31.7% of the total) occurred with a single individual. Vismia Iatifolia and Belluciagrossularoides occurred in all reforestations and systematically presented the highest M values, followed by Laetia procera and Vismia cayennensis, which no longer occurred in only two years of planting. A brief analysis of the dispersal mode of the seeds, the diametric and altimetric distributions were also analyzed.
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