Floristic and structural characterization of tree vegetation in a Deciduous Seasonal Forest sector, RS state, Brazil

Abstract

The objective of the study was to evaluate the floristic and structural composition of an area located in a section of secondary Forest, in the municipality of Dona Francisca, RS state. To do so, 50 permanent plots with a dimension of 10 x 20 m (200 m²) were installed in a systematic way, 10 m apart and 40 m between tracks, totaling 1 ha. All individuals with CAP ≥ 15.7 cm were identified and sampled and the phytosociological estimators were calculated. The species accumulation curve was used to verify the sample adequacy. For the calculation of diversity and dominance estimators, the Shannon Index (H ‘) and Pielou Equability (J’) were used. Subsequently, the floristic and structural composition was evaluated through the Distributed Correspondence Analysis (DCA). It was also verified the diameter and histopic distribution of the tree community, and for the species, with importance value above 5%, the distribution in classes of DAP. Statistical analyzes were performed in the R program. 65 tree and shrub species were identified with 2,045 individuals distributed in 31 botanical families. The species with a value of importance above 5% were Casearia sylvestris (14, 04 %), Nectandra lanceolata (12, 86 %), Cupania vernalis (9, 57 %), Guarea macrophylla (7,29 %) and Ocotea puberula (5.07 %). The values for diversity and dominance were, respectively, 2.91 nats.ind^-1 and 0.69, indicating that the area has low diversity and dominance of few species and that by DCA it is possible to verify that the plots are homogeneously distributed in the forest. The diameter distribution represented the expected behavior for the arboreal community with J-inverted tendency and the majority of the trees presented height concentrated in the middle stratum of the forest. Only Nectandra lanceolata and Ocotea puberula did not present negative exponential curve from the five species analyzed. It was possible to observe the mosaic of tree species distributed in the forest section. In addition, there is a predominance of individuals in the first classes of DBH and height, which characterizes the resilience of the area after the disturbance and its capacity for natural recovery. It also indicates the fluctuations and stability of species in ecological succession of a forest in an intermediate stage of regeneration.

Keywords:
Phytosociological estimators; Secondary vegetation; Spiegel method