Invasive Japanese knotweed (Reynoutria japonica Houtt.) and related knotweeds as catalysts for streambank erosion

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.

Japanese knotweed increases soil erosion on riverbanks

“…Moreover, the absence of vegetation reduces the roughness of the riverbank, accelerating runoff and increasing its erosive force (Hopkinson & Wynn, 2009; Thorne & Furbish, 1995). Although knotweed has a large underground biomass, the rhizomes do not prevent soil surface erosion, nor compensate for the loss of aerial plant structures, which are no longer present to trap sediments (Colleran et al, 2020).…”

“…Increased erosion is nevertheless highly plausible, as knotweed forms monospecific stands whose aerial stems senesce following the first frosts. The dead stems may be swept away during winter and spring floods, denuding the soil (Colleran, Lacy, & Retamal, 2020). Without this biomass, riverbank roughness is reduced (Hopkinson & Wynn, 2009; Thorne & Furbish, 1995).…”

“…The interaction between vegetation and riverbank stability is complex, and a multitude of factors influence this dynamic, such as the soil type, water flow, or pore water pressure (Van de Wiel & Darby, 2007). Nevertheless, one may question whether the competitive displacement of a dense belowground biomass of fine roots less than 50 cm deep by a network of knotweed rhizomes could accelerate riverbank erosion (Colleran et al, 2020).…”

Shade Avoidance and Light Foraging of a Clonal Woody Species, Pachysandra terminalis

“…Clonal plants produce their offspring via not only sexual reproduction but also asexual reproduction, in which new individual clones with an identical gene set, called ramets, are generated [ 1 , 2 , 3 , 4 , 5 , 6 ]. Elucidating the mechanism by which clones forage resources in heterogeneous environments is a central issue in clonal plant ecology [ 4 , 5 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 ], plant growth modeling [ 23 ], and their application in vegetation management [ 17 , 18 , 19 , 20 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 ]. Additionally, the spatial arrangement of ramets determines the reproductive success of clonal plants; this is because aggregation of ramets that belong to the same genets leads to an increased percentage of geitonogamous self-pollination [ 6 ].…”

Invasive Plants in Support of Urban Farming: Fermentation-Based Organic Fertilizer from Japanese Knotweed

“…F. japonica causes considerable economic and environmental damage throughout the USA, UK, and Europe [1,2]. Due to its ability to quickly spread, it reduces the diversity [3][4][5] and the activity [6] of native biota, increases soil erodibility [7], affects temporal patterns of soil nutrient availability [8], and causes significant structural and functional changes in urban and rural ecosystems [9]. As such F. japonica poses considerable economical, planning, and logistical problem in urban and rural land management [10].…”