In Costa Rica, reforestation programs with indigenous tree species are a recent activity. Information is still scarce on long-term species performance and silvicultural management to ensure the success of tree plantings, especially for mixed stands. This study aims to estimate growth, aboveground biomass, and carbon sequestration of nine native tree species growing in mixed and pure plantings. The study was carried out at La Selva Biological Station in the Caribbean lowlands of Costa Rica. More than a half of the tree species studied (e.g. Calophyllum brasiliense, Jacaranda copaia, Terminalia amazonia, Hyeronima alchorneoides, Vochysia ferruginea, Balizia elegans) are distributed from Mexico-Guatemala to South America and a few have more limited distribution in Central America (e.g. Vochysia guatemalensis, Virola koschnyi, Dipteryx panamensis). The nine tree species are divided into three sets. The 3 members of each set were grown separately in pure plantations, and together in 1 mixed plantation, giving 12 monocultures and 4 mixtures. Plantation 1 (13 years old) is composed of V. guatemalensis, C. brasiliense, and J. copaia. Plantation 2 (13 years old) is comprised of D. panamensis, T. amazonia and V. koschnyi. Plantation 3 (12 years old) is composed of H. alchorneoides, B. elegans, and V. ferruginea. Overall, all the species had good growth and productivity either in pure or mixed stands in comparison to other native and exotic species growing in similar ecological conditions. The exception was C. brasiliense in mixed stands, where it was suppressed by the fast-growing species V. guatemalensis and J. copaia. At the stand level, the mixed stands performed well for volume, basal area, aboveground biomass, and carbon sequestration, in comparison to other pure or mixed plantations of tropical timber species. Pure plantations of V. guatemalensis, V. ferruginea, V. koschnyi, J. copaia, and T. amazonia also presented good productivity. At the tree level, V. guatemalensis, J. copaia, T. amazonia, H. alchorneoides, and D. panamensis performed better in mixtures than in pure stands for diameter, height, aboveground biomass, and carbon sequestration estimations. Values for the former three species were significantly higher in mixed than in pure stands. C. brasiliense was the only species with significantly better growth in pure stands than in mixed stands, for the three-species combination examined. The results show that mixed plantings had similar or higher productivities for several of the variables examined, but conclusions on relative productivities depend on the species and growth features, interactions among species, and the variables quantified. In addition, there is a need to continue monitoring over longer time-frames, and for further studies of the species interactions and site factors involved, in order to develop reforestation guidelines for a range of objectives and environmental settings.