Ecologia da regeneração de espécies arbóreo-arbustivas em savanas: o papel das árvores nucleadoras

Abstract

The objective of this study was understand the restoration and self-regeneration patterns under the influence of the crown of four dominant tree species (nursery-tree or nucleation-tree) in the Roraima’s savanna (lavrado), northern of Brazilian Amazonia: Curatella americana L., Byrsonima crasssifolia (L.) H.B.K, Byrsonima coccolobifolia Kunth and Roupala montana Aubl. The study took into account the composition, richness (S) and diversity index (Shannon-Weaver) of tree and scrub plants surveyed under the crown of these nucleation species, besides to take a comparison of results through the Sørensen’ index of similarity. Were also assessment the onthogenic stages (sapling, young and established) and the spatial distribution pattern of these individuals under the crown of observed species. The results showed that the nursery-trees have strong relationship with edaphic factors, specially texture and aluminum saturation, and that this is related to the plant diversity under their crowns. It was verified that the nucleation effect of the studied species was markedly higher to self-regeneration, mainly in the simpatric species of the genus Byrsonima (48% to B. crassifolia and 46% to B. coccolobifolia) and in smaller degree to R. montana (12 %) and C. americana (6%). Richness and diversity of tree and scrub plants was larger under the crow of C. americana (S = 16; H’ = 1,389-1,824); R. montana (S = 13; H’ = 1,453-1,992), B. coccolobifolia (S = 12; H’ = 0,669) and B. crassifolia (S = 10; H’ = 0,864-1,908). Most of the tree and scrub individuals found under the crown influence area of B. coccolobifolia was of B. coccolobifolia (46%) while for B. crassifolia were of B. crassifolia (48%). Under C. americana the specie Randia formosa (33%) was more yisibie while for R. montana the species more important were Connarus favosus and B. crassifolia with 23%. Some surveyed species under the crown of the nucleation-tree (B. crassifolia, Eugenia punicifolia, Erythroxilum suberosum and Xylopia aromatica) are species without nutritional demand for their establishment, while C. americana and Rourea grosourdyana demanded basicity. The results suggest that conditions of constant environmental stress (high rain sazonality and low fertility soils), associate to strong anthropogenic pressure (fire), transmit to the nucleation species of this ecosystem an important role in the maintenance and formation of the plant diversity in the Roraima’s savanna, generating favorable effects to the recruitment and the maintenance of regional plants. The substitution of these nursery-trees (resistant and adapted to the local conditions) for other exotic ones (no adapted) can generate harmful effects to the environment, with direct consequences related to the loss of the regional biodiversity. Nursery-trees of the Roraima’s savanna are constituents of the environmental restoration system.