In separate experiments, tolerance of root competition and of flooding were assessed for seedlings of Chinese tallow tree (Sapiumsebiferum(L.) Roxb.), an invasive species in some North American floodplains. In the root competition experiment, pots containing seedlings of Chinese tallow tree and a native North American floodplain species (green ash,FraxinuspennsylvanicaMarsh.) were buried in the soil of a closed-canopied floodplain forest in South Carolina. Approximately half of the pots were invaded by roots of surrounding vegetation. In both species, total seedling mass in invaded pots was 70% of that in uninvaded pots. In the flood tolerance experiment, potted seedlings of tallow tree and a highly flood-tolerant species (water tupelo,NyssaaquaticaL.) were subjected to flooded and well-drained treatments in two light regimes: 20 and 100% of full sunlight. Mortality of flooded tallow trees was lower than of flooded tupelos (0 vs. 7.5%). Growth reductions under flooding were similar for both species in 20% light, but greater for tallow tree than for tupelo in 100% light. Flooded tallow trees produced hypertrophied lenticels and adventitious roots. Sensitivity to root competition and high flood tolerance may explain why seedlings of Chinese tallow tree are concentrated in low wet areas of floodplain forests.