Effects of Pittosporum undulatum Vent. invasion on forest diversity and structure in Southern Brazil

Abstract

ABSTRACT Invasive alien species are considered the second largest cause of biodiversity loss in the world. Pittosporum undulatum Vent., is a native species to Australia and was introduced to Brazil, currently being considered invasive in several regions. Here we analysed the floral and structural composition of forest fragments with varying degress of biological invasion by P. undulatum and assess the relationship between its presence and community diversity. A phytosociological survey was conducted in disturbed and reference forests within two forest fragments in Southern Brazil, assessing tree species diversity, structural and environmental variables between communities across all ontogenetic stages. We recorded 7554 individuals from 35 botanical families and 87 species at all ontogenetic stages, including adults, saplings, and seedlings. P. undulatum showed the highest importance in the adult and sapling stages. The presence of P. undulatum in the forest community is not affecting the richness and diversity of the fragments when the communities were analysed separately (as disturbed and reference forests), but we may see their effect when all forests were analysed together in different ontogenetic stages. In addition, there was a reduction in basal area with advancing successional stages, contrary to typical patterns found in mature forests. The presence of P. undulatum in the reference forest suggests that this species is invading older, more established forests.