Invasive Japanese knotweed (<i>Reynoutria japonica</i> Houtt.) and related knotweeds as catalysts for streambank erosion
Brian Colleran, Shaw Nozaki Lacy, Maria Rafaela Retamal
Abstract
Abstract Japanese knotweed (Reynoutria japonica) and the other invasive knotweeds, collectively known as knotweed s.l. , are significant invasives worldwide, especially of riparian areas. While R. japonica and other knotweed s.l. can reproduce sexually, their dispersal to and spread within new regions is often accomplished through vegetative reproduction from rhizome and stem fragments. Once established, knotweed s.l. can displace riparian plants, meaning that soil stability once provided by displaced roots is lost, carrying significant knock‐on implications for watershed management. We propose that knotweed s.l. rhizomes both displace roots and the structure they provide to soil, and also amplify bank‐erosion forces, especially during floods. Further, erosive forces create propagules, with larger flow events creating larger numbers of propagules and providing the vector for short‐ and long‐distance downstream spread within the watershed. Induced erosion is therefore the main driver of knotweed s.l. invasions along waterways. As some hydrological regimes shift towards more frequent and severe storm events in response to climate change, positive feedback loops may develop in these regions between existing knotweed s.l. populations, sudden riverbank failure, and increased flood‐related damage, with presumably significant impacts on riparian infrastructure. While the continued spread of this invasive could have significant riparian flood resiliency consequences if left unchecked, mindful action to control these plants is likely to be beneficial financially, socially, and ecologically within any invaded watershed.