The main objective of this study is to characterize the floristic richness, phytosociological structure, and classify the ecological groups of the adult tree component species in an area of ecological tension (Seasonal Forest and Caatinga) in Pernambuco - Brazil. The study was conducted in Atlantic Forest stretch in Pernambuco – Brazil, from April 2019 to February 2020. Methods adopted for this study includes the allocation of 20 plots, with dimensions of 10 m x 25 m, spaced in 25 m. Each adult individual, with a circumference at breast height (CBH 1.30 m) ≥ 15 cm, was identified in the field. The softwares Mata Nativa version 2 and Excel 2019 were used to process the collected data. Sample sufficiency, classification of ecological groups, diversity and phytosociology were analyzed. As a result of the research, the density of the adult tree component in the fragment was 1,888 indha-1 and the dominance was 21.64 m².ha-1. These values are following the standards of other studies in Atlantic Forest in the State of Pernambuco. The botanical families with greatest richness are, respectively, Fabaceae, Myrtaceae, Annonaceae, Lauraceae, Elaeocarpaceae, Sapindaceae and Sapotaceae. Regarding the ecological groups, 46% of the species were classified as initial secondary. The species of greatest Value of Importance were Guapira nitida, Buchenavia tetraphylla, Manilkara sp., Byrsonima crassifolia and Sloanea obtusifolia, respectively. The Shannon-Wiener Diversity Index (H') value was 3.21 nats.ind-1 and the Pielou Uniformity Index (J) was 0.73. According to the results obtained, the development process of the adult tree component of the fragment was directly affected by the pasture matrix. However, species diversity has not been compromised, indicating the area's resilience potential.
