Dinâmica da composição florística e abundância de espécies arbóreas em uma área explorada e submetida a tratos silviculturais na Floresta Nacional do Tapajós.

Abstract

In order to improve tíie sustainable management ofthe tropical forests it is necessaij' to know how they replace treir resources, the dynamic process of the natural regeneration and the qualitativo and quantitative potential. The forest dynamics refers to the changes that occur on floristic and forest structure through the time. In this study, changes that occurred ín a dense tropical forest area, after logging and silvicultural treatments are presented, to improve the technical and scientifíc knowledge on natural forest ecology. The objective of the research was to evaluate the dynamics on floristic composition and abundance in a 144 ha area in the Tapajós National Forest as an ecological basis to improve silvicultural systems to that area which is located in km 114, BR 163, Santarém-Cuiabá road, municipality ofBelíena, PA. The statistical design was randomized blocks wíth four replications per block; TI - logging of trees > 45 cm DBH from 38 species; T2 - logging of trees > 55 cm DBH from 38 speoies, plus silvicultural treatment 12 years after logging to reduce basal area on 20%; T3 - logging oftrees > 55 cm DBH from 38 species, plus silvicultural treatment 12 years after logging ío reduce basal area on 40%; T4 - logging of trees > 55 cm DBH from 38 species, plus silvicultural treatment 12 years after logging to reduce basal area on 60%. Floristic composition and abundance of species vvere analysed in four occasions in a 14-year períod The logging as well as the silvicultural treatments influenced the dynamics on floristic composition and abundance oftree species. The number offamilies and tree species increased up to the seventh year after logging. The families and the species more responsible for the dynamics of floristic composition were; Araliaceae {Schefflera morototoní), Caricaceae {Jacaratia spinosa), Caryocaraceae (Caryocar villosum), Lacistemataceae (Lacistenm agreggatum), Malpighiaceae (Byrsomma crispa), Monímiaceae (Siparuna decipiem), Opilíaceae (Agonandra sp.), Rutaceae {Pagara pentandrd), Sapindaceae {Talma sp.), Solanaceae {Solannm rugosum), Theophrastaceae {Clavija lancifolia) e Vochysiaceae {Vochysia surinamemis). The commercial species which had their timber harvested were those that had their abundance more altered because ofthe logging, but líghtly altered by the silvicultural treatments. The species that were not harvested were just a few dynamic, exception for those veiy light-demandíng. Those light-demanding species tliat liad the number oftrees reduced by cutting or damage oflogging were more dynamic on floristic composition as well as on abundance.