Penn, Michael, Geography Department, Binghamton University, 263 Rotary Rd., Chemung, NY 14825, mpenn1@binghamton.edu; Blumler, Mark, A, Geography Department, Binghamton University, Old Johnson Building, 4400 Vestal Pkwy E 102 B, Vestal, NY 13850, mablum@binghamton.edu.
Invasive knotweed (Reynoutria spp.) is a group of highly invasive plant species in Europe and America. Using remote sensing data of river islands, I found that knotweed patches expand in open ground 48-112 cm/yr. Patches downstream of a large wastewater treatment plant grew faster than those upstream, implicating nutrient pollution as possibly facilitating knotweed invasion. I estimate that knotweed has been in the Upper Susquehanna River Valley since at least 1961 and that it spreads principally during the largest floods. Knotweed’s establishment rate is approximately one patch per 3000-4200 m2. Knotweed is excluded from areas of frequent flooding with heights of 0-1 m above typical water level being a preliminary approximation for river islands and 2 m for a floodplain. Such flooding likely excludes knotweed from 13-43% of such riparian areas. I also determined that knotweed causes soil aggradation below its canopy.
I conclude that preserving topographic diversity of riparian areas is likely to lessen knotweed’s negative effects on biodiversity. I recommend that rapid-response activities focus efforts on a stream’s largest floods and that they be performed after a one growing season delay. Future studies should determine whether knotweed can concurrently cause both soil aggradation as well as bank mass failure, whether stabilization of streams encourages knotweed monocultures, and whether nutrient pollution facilitates knotweed invasion.
invasive knotweed, erosion, geographical spread, flooding