Effects of Chinese privet (Ligustrum sinense) invasion on decomposition and litter-dwelling invertebrates in Southeastern U.S. floodplain forests

Abstract

Chinese privet (Ligustrum sinense) is one of the most problematic invasive plants in many parts of the world where it often dominates the shrub layer in riparian forests. We aimed to evaluate the role of privet invasion on litter inputs, rates of litter decomposition and litter-dwelling arthropods in the Southeastern United States. To do this we: (1) evaluated the relative contribution of privet to total litter-fall, (2) compared breakdown of artificial leaves (filter paper) in plots which had or had not been subjected to experimental privet removal, and (3) compared litter breakdown and arthropod communities among the following litter types: (a) native sweetgum, (b) invasive Chinese privet, and (c) a mixed sweetgum–privet litter treatment. Privet accounted for 10% of annual litter-fall at our study sites and leaf fall phenology differed from native species. Filter paper decomposed about twice as quickly in reference compared to removal plots but there were no differences between plot types in litter decomposition. This difference may relate to flooding during the litter bag experiment. In both plot types, privet litter decomposed faster than sweetgum or mixed litter but there were no differences in decay rates between the latter two litter types, suggesting that sweet gum may slow the rate of decomposition in mixed bags. There were no differences among litter or plot types in invertebrate community composition or overall abundances, but detritivores were marginally more abundant in the reference plots. Our findings suggest that flooding may affect the impact of privet invasion on litter decay rates and associated invertebrate communities.