Background/Question/Methods   Invasive plant species can alter ecosystem processes by changing rates of decomposition and nutrient flux through ecosystems.  Riparian systems experience regular disturbance, and associated aquatic systems are highly dependent on riparian leaf litter as a source of nutrients.  The recent appearance of Ailanthus altissima Swingle (tree-of-heaven) in riparian systems in the southeastern U.S. may alter the aquatic decomposition rates of litter from native tree species, as previous work has demonstrated that litter in species mixtures decomposes at rates that cannot be predicted from decomposition rates of single species.  As an invasive species capable of forming large monocultural stands, Ailanthus may affect aquatic systems not just in terms of the presence of its leaf litter but also by the relative abundance of litter inputs.  We designed an experiment to test whether Ailanthus leaves and leaves of the native riparian tree Platanus occidentalis L. (sycamore) decomposed at different rates in mixtures with varying proportions.  We conducted a short-term aquatic decomposition study in which leaf litter were decomposed in the following proportions: 100% Ailanthus, 100% Platanus, 50% Ailanthus and 50% Platanus, 33% Ailanthus and 67% Platanus, and 67% Ailanthus and 33% Platanus. 
Results/Conclusions    Results suggest that mixing litter of a native and non-native species changes decomposition rates for both species, and that changing relative proportions of litter also changes decomposition rates.  In both Ailanthus and Platanus litter from the last removal date, percentage of mass remaining of the species when rare (33% Ailanthus or Platanus) was comparable to mass remaining when the species was decomposed alone (100% Ailanthus or Platanus).   In contrast, we found that when a species was present in equal proportion or dominant in a mixture (50% or 67% Ailanthus or Platanus), decay rates were similar and were reduced in comparison (65% reduction in mass loss Ailanthus, 28% reduction in mass loss Platanus) to rates of species decomposed alone.  These results suggest that the presence of Ailanthus affects aquatic decomposition rates, but that these effects may not be directly proportional to the abundance of Ailanthus within riparian systems.