Changes in plant community of Seasonally Semideciduous Forest after invasion by Schizolobium parahyba at southeastern Brazil

• A native species from the Evergreen Atlantic Forest is invading the Seasonally Semideciduous Forest in the same country.
• We compared the plant assemblage under the invasive, under a native equivalent species, and randomly in the forest.
• Plant density, basal area, and richness were remarkably lower under the invasive trees compared to the other plots.
• The invasive tree changes the structure and composition of the understory, thus impairing the forest dynamics.

The recognition of a species as invasive is generally accepted when it comes from another continent or even from another country, but requires strong evidences of negative impacts to support control actions when the invasive species comes from another region in the same country. Schyzolobium parahyba – the ‘guapuruvu’, is a Brazilian tree native from the evergreen type of the Atlantic Forest, which has been recorded as invader in a number of remnants of the Seasonally Semideciduous Forest – SSF. We hypothesized that this giant and fast growing invasive tree changes the structure and composition of the understory, thus impairing the forest dynamics. We assessed the invasive population in the whole fragment, and, within the portion invaded, we sampled the regenerating plant community 1) under the largest alien trees, 2) under a native species with similar ecology (Peltophorum dubium), and 3) randomly in the forest. Density, basal area and richness under S. parahyba were remarkably lower than under the equivalent native species or in the understory as a whole. Floristic composition of the plant community was also distinct under S. parahyba, possibly due to increased competition for soil water. Even though the alien species has occupied, as yet, a small proportion of the forest fragment, it dominates the overstory and threatens the regeneration processes under its canopy. In view of our findings, we recommend extirpation of the species from SSF, as well as avoiding cultivation of the species away from its native range.