Japanese knotweed (Fallopia japonica) is a water-bourne exotic weed currently invading the riparian zones in the United States and Europe. We mapped the distribution of knotweed in three watersheds in upstate New York and contrasted the incorporation of knotweed and native plants into food webs.
Results/Conclusions
Knotweed invasions were more common in streams with greater discharge rates (third to fifth order versus smaller headwater streams) and the incidence of invaded stands was greatest in the depositional banks of meandering stream segments. We attribute both these distribution patterns to changes in the rate of delivery and deposition of plant fragments. Knotweed is poorly integrated into the riparian and in-stream food webs. Mean defoliation rates among 31 native plant species were almost three times higher than for knotweed (mean ± SD = 14.5 ± 6.5 and 6.6 ± 5.3, respectively). In-stream processing rates of knotweed were slower than five other native tree species, and knotweed leaves were colonized by different in-stream invertebrate communities. The knotweed invasion is facilitated by a readily available transportation network (flowing rivers) and a paucity of effective natural enemies, and our results suggest it may alter in-stream animal communities.
