Regenerating forests are important for the maintenance of tropical biodiversity. Forest management in fragments of Atlantic forest in Brazil includes removal of exotic eucalyptus trees that were once part of plantations, in order to reestablish native flora. However, it is unclear how native tree saplings regenerating under former plantations respond to abrupt changes in environmental conditions associated with exotic tree removal. We used leaf carbon isotope composition (δ 13 C) and photosynthetic parameters to evaluate physiological responses of native tree saplings to canopy opening. We analyzed young and mature leaves of the three most representative species of regenerating trees (Byrsonima sericea, Siparuna guianensis, Xylopia sericea) in one secondary forest fragment and three managed areas that form an irradiance gradient (9, 85, 230 and 550 µmol m -2 s -1 ) in Brazilian Atlantic forest.Eucalyptus removal increased photosynthetic CO 2 assimilation and stomatal conductance in