Phytosociological parameters

Invasive alien species are considered the second biggest cause of biodiversity loss in the world. <i>Pittosporum undulatum</i>, a native species to Australia and introduced to Brazil is considered invasive in several regions. In this study, we analyze the floral and structural composition of forest fragments with varying degrees of <i>P. undulatum</i> invasion and examine the relationship between species presence and community diversity patterns. A phytosociological survey was conducted in two forest fragments, assessing environmental and diversity variables. We sampled trees at all growth stages, including adults, saplings, and seedlings. A total of 7554 individuals from 35 botanical families and 87 arboreal and arborescent species were sampled. <i>Pittosporum undulatum</i> was the most important species in the adult and sapling stages. The Disturbed Forest showed greater richness, basal area, individual density, canopy opening, and diversity. Despite the high bioinvasion of the species, it did not change the richness and diversity of the fragment, presenting higher values than several native fragments of the region. There was a reduction in basal area with advancing successional stages, contrary to typical patterns in Atlantic Forest. The presence of IAS in the Reference forest alerts to a possible bioinvasion process in older forests, especially after disturbances occur.