Decomposition of Leaf Litter from Native and Nonnative Woody Plants in Terrestrial and Aquatic Systems in the Eastern and Upper Midwestern U.S.A.

Leaf litter decomposition plays an important role in nutrient cycling in both terrestrial and aquatic systems. Decay rates vary based on species, habitat, climate, and local environmental conditions. Invasive plants alter decomposition processes; however, there is a lack of research exploring patterns at regional and continental scales. In this study we examined the decomposition of both native and nonnative, invasive woody plant leaf litter and mixtures of the two, in both terrestrial and aquatic habitats at nine locations in the eastern and midwestern U.S.A. There was significant variation among locations, which was not clearly related to either average air temperature or precipitation. Unexpectedly, in locations with multiple years of data, there were higher rates of decomposition in years with lower temperatures and precipitation in both terrestrial and aquatic habitats. We found decay rates were generally higher in aquatic than terrestrial habitats and leaf litter from nonnative invasive species generally decayed faster than that of native species in both terrestrial and aquatic systems. Differences in litter decay rates among invasive species were significant in both terrestrial and aquatic habitats; whereas no differences were found among native species in either habitat. In mixed litter bags, decay rates were lower than what was predicted based on the relative amounts of native and invasive litter in each bag, possibly indicating the presence of native leaf litter slows the decomposition of invasive leaf litter. Additionally, there may have been threshold effects in the mixed litter bags, especially in aquatic systems. While this study supported several generalizations about leaf decomposition rates (invasive > native, aquatic > terrestrial), the variability in the decay rates from different locations and habitats indicates combinations of different species and local conditions may overshadow other general trends related to litter decomposition.