Ailanthus (tree-of-heaven) is a prolific nonnative invasive tree invading disturbed areas in the eastern United States, including managed forests. Its success is often attributed to a superior competitive ability. Forest Service scientists compared the competitive ability of ailanthus with staghorn sumac in a greenhouse and in a common garden trial. Different density combinations and light levels were evaluated in the greenhouse over three months, and the same densities were examined in the common garden over two growing seasons. Tree height and shoot and root biomass were measured. In the greenhouse and common garden, sumac grew faster and had greater shoot and root biomass than ailanthus in every density combination and light treatment. The root-to-shoot ratio of ailanthus was higher than that of sumac under greenhouse high-light treatments; preliminary data show the same in the common garden at density combinations with more ailanthus stems than sumac, suggesting that ailanthus, given adequate light, puts more energy into root development than sumac. Sumac and similar early successional natives may be able to prevent invasion by nonnative invasives like ailanthus at disturbed sites, highlighting the importance of maintaining native seed and seedling banks.