Implications of extreme flooding events modifying fluvial geomorphology for dispersal of knotweed (Reynoutria spp.) in the wake of climate change

Implications of extreme flooding events modifying fluvial geomorphology for dispersal of knotweed (Reynoutria spp.) in the wake of climate change | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Implications of extreme flooding events modifying fluvial geomorphology for dispersal of knotweed (Reynoutria spp.) in the wake of climate change Sarah Demian, Aidan Anderson, Jaylene Braithewaite, Lauren Mckenna, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7456717/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 04 Jan, 2026 Read the published version in Biological Invasions → Version 1 posted 5 You are reading this latest preprint version Abstract The knotweed species complex ( Reynoutria spp.) constitutes one of the most invasive plant taxa globally. Knotweed dispersal mechanisms facilitate rapid spread along waterways. The 100-year Pacific Northwest flood of November 2021 impacted British Columbia’s Vedder-Chilliwack River and its biota both through historically high rates of discharge and altered fluvial morphology including formation of new islands in the river and removal of existing vegetation. According to our field surveys, a five-fold increase of knotweed patches was observed in 2022 along the Vedder-Chilliwack River as compared to 2019. Much of the knotweed population increase occurred in newly available disturbed areas created by the flooding. Knotweed patches in the river’s tributaries tended to be well-established whereas the age distribution in the mainstem was skewed towards younger age intervals, indicating tributaries may act as a major source of population growth if not controlled. Knotweed in densely concentrated areas along the river was resurveyed in subsequent summers. Knotweed continued to expand, with 21% more patches in 2024 than in 2022 followed by a 97% increase in 2025 relative to 2024. The near doubling of the knotweed population in 2024 was likely connected to a significant rainfall event in October 2024. Both the 2021 and 2024 flooding events are consistent with the global increase in flooding frequency and intensity due to climate change. Such flooding events can significantly contribute to the expansion of invasive plant populations in waterways, highlighting the crucial need for targeted management in river systems to mitigate further spread across watersheds. knotweed rivers flooding climate change rhizome spread invasive species Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Introduction Japanese knotweed ( Reynoutria japonica ) and giant knotweed ( Reynoutria sachalinensis ), both members of the Polygonaceae family, are herbaceous perennials native to East Asia including Japan, Korea, and parts of China (Drazan et al. 2021 ). Knotweeds were introduced to North America in the late nineteenth century as ornamental plants (Barney 2006 ). Knotweed had already been introduced to Europe earlier in the nineteenth century, also as a prize-winning ornamental plant which initially commanded large sums of money (Bailey and Conolly 2000 ). In both North America and Europe, a hybrid of Japanese and giant knotweed forms referred to as Bohemian knotweed ( Reynoutria × bohemica ) occurs which is also very invasive (Neupert et al. 2021 ). Knotweeds are now recognized as among the world’s most invasive species due to their strong competitive and dispersal abilities, which allow them to rapidly form dense patches that displace native vegetation and are extremely difficult to remove (Gillies et al. 2016 ). They outcompete native vegetation by blocking sunlight and releasing allelopathic compounds, which are chemicals that inhibit the growth of surrounding vegetation (Gillies et al. 2016 ). While hybrid populations ( R. × bohemica ) produce viable seeds, R. japonica regenerates almost exclusively from rhizomes because the introduced biotypes produce very little pollen (Barney et al. 2006; Smith et al. 2007 ; Gillies et al. 2016 ). Here we will refer to Reynoutria spp. as “knotweed” because all three related taxa coexist in many parts of North America, including on the west coast. Knotweed species are a high priority for management in Europe and North America including the Pacific Northwest region of North America specifically because they pose serious threats to ecosystem health and human infrastructure (Gaskin et al. 2014 ; Gillies et al. 2016 ). All three Reynoutria species have been listed as Noxious Weeds under British Columbia’s Weed Control Regulation (Government of British Columbia 2022 ). Both Oregon and Washington classify knotweed as Class B noxious weeds, meaning that they require control in locations where not yet widespread (Washington State Noxious Weed Control Board 1995 ; Oregon Department of Agriculture 2024 ). Knotweed is also listed on the Pacific Northwest states’ quarantine lists; therefore, transport and distribution of knotweed plant parts is prohibited. These legislative measures reflect the shared recognition across the Pacific Northwest that knotweed poses a severe and ongoing threat. Knotweed has spread extensively through human activity and now climate-induced floods and has a reputation for damaging infrastructure and undermining riverbank stability (Colleran et al. 2020 ; Matte et al. 2021 ; Kaehler 2023 ). Excavating knotweed is generally not a successful eradication method due to the regenerative nature of knotweed, unless from tiny fragments in an EDRR context (Colleran and Goodall 2014 , 2015 ). For mature plants, successful excavation must include the area surrounding a patch of knotweed as the rhizomes can extend at least ten metres from the parent plant or more (Child and Wade 2000 ; Fennel et al. 2018). Herbicides are regarded as the only consistently effective methodology against knotweed growth; however, they are prohibited for use in many environmental regions in British Columbia such as along waterways (BC Ministry of Environment 2016). A major reason to seek effective management and/or eradication strategies is that beyond risks to the built environment, knotweed facilitates riverbank erosion (Arnold and Toran 2018; Hammer 2019; Matte 2021; Kaehler 2023 ; Penn 2024), presumably because the rhizome-dominated underground portion of the plant lacks root hairs, and therefore does not bind to the soil. Additionally, the rhizomes are concentrated in the surface layer, under which there are many fewer rhizomes. Having eliminated the variety of depth and form that the displaced floral species provided, no vegetation remains to bind the soil (Child et al. 1992 ; Aguilera et al. 2009 ). Furthermore, mycorrhizae are reduced by knotweed allelochemicals (Kato-Noguchi 2022 ), which would weaken yet another aspect of soil cohesion. Growth can occur from very small rhizome and stem fragments that include at least one node (De Waal 2001 ; Sásik and Pavol 2006 ). Roadways frequently become infested with knotweed as activities such as mowing can transfer rhizome and stem fragments to new locations. Knotweed grows abundantly near waterways as stem and rhizome fragments, as well as seeds, can spread through rivers due to their buoyant nature (Rouifed et al. 2011 ; Drazan 2021). Similarly, flooding encourages the growth of knotweed as plant fragments are brought downstream to then form new stands. Colleran and Goodall ( 2014 ) found that following a flooding event in Vermont, 70% of new knotweed plants originated from rhizome fragments, while 30% originated from stem fragments. By contrast Rouleau et al. ( 2023 ) observed that all the new plants were sourced from rhizome fragments following flooding in Québec. Invasive species tolerate a broader spectrum of environmental conditions than native species (Flanagan et al. 2015 ). Not only does climate change make ecosystems more susceptible to invasive plants, but invasive plants worsen climate change impacts on ecosystems (Mainka and Howard 2010 ). Riparian ecosystems are key points for climate and invasive species interactions (Flanagan et al. 2015 ). Climate change and invasive species interact synergistically, with climate change promoting evolution of invasive plants (Ziska et al. 2019 ; Clements and Jones 2021 ). Knotweed is very adaptable. At least six major mechanisms promote rapid knotweed evolution: polyploidy, hybridization, local adaptation, clonal growth, phenotypic plasticity, and epigenetics (Clements and Jones 2021 ). Polyploidy and hybridization facilitate knotweed’s tolerance across a relatively broad range of ecological conditions (Clements and Jones 2021 ; Anatskaya and Vinogradov 2022 ). Local adaptation refers to knotweed’s ability to adjust to specific environmental conditions, while clonal growth occurs through vegetative propagation via extensive rhizome networks (Clements and Jones 2021 ). Knotweed exhibits phenotypic plasticity, with genotypes capable of producing a range of phenotypes in response to varying environmental conditions (Clements and Jones 2021 ). Flexibility in gene expression via epigenetics enables quick adjustments by knotweed to environmental stressors, making epigenetic effects advantageous for knotweed invasion (Jones 2012 ; Asensi-Fabado et al. 2017 ; Clements and Jones 2021 ). Knotweeds utilize these six mechanisms differently depending on environmental circumstances, making them more adaptable to extreme environmental conditions compared to native vegetation (Parepa et al. 2014 ; Duquette et al. 2016 ; Gillies et al. 2016 ; Clements and Jones 2021 ). The November 2021 Pacific Northwest floods prompted a state of emergency for British Columbia (Zussman 2021 ). Slide damage, bridge collapses, and floodwaters were recorded across southwestern British Columbia in Merritt, Abbotsford, Princeton, and Chilliwack (Gillett et al. 2022 ). Due to human-induced climate change, the probability of an atmospheric river that generated the intense rainfall experienced during the 2021 event increased by more than 60% since the pre-industrial climate; what was once a 1 in 20.7-year event is now calculated to be a 1 in 11.8-year event (Gillett et al. 2022 ). The high precipitation was the primary contributor to the extreme streamflow, but snowmelt from the rapid temperature rise during the 2021 heavy rainfall event also made a significant contribution (Gillett et al. 2022 ). This natural disaster was the most expensive in British Columbia’s history (Gillett et al. 2022 ), and many factors, such as the potential spread of invasive plants due to the floods, have yet to be accounted for in the cost analysis. Fluvial geomorphology and invasive plant spread are closely connected (Wieting et al. 2023 ; Hardwick et al. 2025 ). Along the Vedder-Chilliwack River, the sheer force of the floodwaters not only eroded riverbanks but also uprooted trees, carrying them downstream where they accumulated on islands. In several locations, bank collapse and sediment redistribution altered the river’s shape and course. Given the abundance of knotweed in the riparian zone, it would not be surprising if dispersal of knotweed would be enhanced. Such hydrologic and geomorphic disturbances can accelerate the spread of invasive riparian plants by both transporting propagules and creating disturbed habitats favourable for colonization (Wieting et al. 2023 ; Hardwick et al. 2025 ). Within the past 50 years there have been occasional instances of discharge levels in the Vedder-Chilliwack River above 500m 3 s − 1 , which correspond to the times of most intense flooding (Ham and Church 2000 ). On November 15th, 2021, the Vedder-Chilliwack River experienced a discharge of over 700 m 3 s − 1 —ten times greater than the mean. This resulted in significant flooding and erosion of the stream banks throughout the river (Government of Canada 2023 ). This provided an opportunity to study the effects of extreme flood events on knotweed dispersal in waterways. Our objectives in this study were to 1) evaluate the population increase and spread of knotweed in the Vedder-Chilliwack River following the extreme flooding event in November 2021, to 2) examine whether particular tributaries were disproportionately responsible for the knotweed spread during flooding, and 3) evaluate the role of alteration of fluvial morphology on invasive plant spread during extreme flooding to help design proactive measures to prevent the spread of invasives under climate change. Materials and Methods Site Description The Vedder-Chilliwack River is over ninety-five kilometres long and flows northwest from its headwaters in northern Washington, USA and empties into the Fraser River in British Columbia, Canada (Fig. 1 ). Near the source of the river in Washington State are kilometres of old-growth forests within the North Cascades National Park. Contrastingly, the portion of the river extending from Chilliwack Lake to the Fraser River is bordered by second-growth forests which have been heavily logged since the beginning of the 19th century (Cleary 2001 ). This logging has had detrimental impacts on the health of this stream by both decreasing stream complexity and increasing erosional risk (Ogston et al. 2015 ). Chilliwack Lake represents a convenient boundary for the purposes of this study, by effectively separating the upstream American portion of the Vedder-Chilliwack River from the downstream Canadian portion. The hydrologic transportation processes are arrested at the lake, thus causing unique hydrology upstream and downstream of the lake (Ham and Church 2000 ). This current study focused on the Vedder-Chilliwack River downstream of Chilliwack Lake from the Tamihi Rapids to Great Blue Heron Park where the vast majority of knotweed patches on the river occur (Fig. 1 ). This portion of the river is characterized as being a high-powered stream with bankfull width ranging from 40 m to 80 m, and a boulder/cobble dominant stream bed (Ogston et al. 2015 ). The average annual discharge in this portion of the stream is 60 m 3 s − 1 (Ham and Church 2000 ). The Vedder-Chilliwack River is a very popular recreational fishing stream, and the river supports a large freshwater sport fishery. Although the river has the two names with the Vedder being the lower portion of the river below the Vedder Crossing Bridge, it will be referred to as the Vedder-Chilliwack River within this paper. Several salmon species migrate into Chilliwack including Chinook, Chum, Pink, Sockeye, and Coho; however, most spawning is restricted to nearby tributaries as mainstem upstream spawning habitat is limited (City of Chilliwack n.d.; Ogston et al. 2015 ). Various types of trout, such as rainbow, steelhead, and coastal cutthroat also make the Vedder-Chilliwack River their home (Tourism Chilliwack 2019 ). This river was recommended as a prime study site by the Fraser Valley Invasive Species Society due to concerns about the abundance of knotweed and the difficulty of controlling it in the Vedder-Chilliwack watershed. Data Collection 2022 Data collection occurred through field surveys of the Vedder-Chilliwack River. From July 4 to August 23, the UTM coordinates of the knotweed patches along the river were recorded by use of two Garmin GPS receivers. The presence or absence of dead stems as well as size, including height, width, and length, were recorded for each patch (by use of measuring tapes). ArcGIS Survey123 was used for recording data and measurements. The heights of tall knotweed patches were measured via Suunto PM-5/1520 clinometers. Surveying efforts were designed to capture as much of the knotweed population as possible, within the constraints of site accessibility. The extent of surveying along the mainstem was based on knowledge of the extent of the infestation, so even though the whole river was not surveyed, very little knotweed occurs outside the surveyed area. On the north side of the Vedder-Chilliwack River, surveys included all knotweed patches located adjacent to the river. All knotweed patches on islands were surveyed in their entirety. On the south side of the river, accessibility was more limited due to private property and dense vegetation. As a result, surveys on the south side were restricted to areas within ten metres of the riverbank. Additionally, ten tributaries were surveyed which had confluences upstream of the Vedder Bridge and downstream of the Tamihi Creek Campground. The wetted width was approximated to form the extent of the surveyed area for each surveyed tributary. Knotweed patches found alongside tributaries were assigned to a size class. The five size classes were: (1) single shoot—less than 50 cm, (2) less than five shoots—less than 100 cm, (3) 5–10 shoots—greater than 100 cm, (4) 10–20 shoots—greater than 200 cm, and (5) more than 20 shoots—greater than 200 cm (Fig. 2 ). These class sizes were modified from the Invasive Alien Plant Program (IAPP) standards and made applicable for knotweed (Kathy Ma Green, Executive Director of the Fraser Valley Invasive Species Society, pers. comm.). Data Collection 2023 In the summer of 2023, we revisited areas that were densely populated with knotweed patches, which accounted for roughly 20% of the total area surveyed in 2022 to obtain a representative indication of population change since 2022. The areas surveyed in 2023 were 1) on the north side of the river near Great Blue Heron Nature Reserve, 2) on the south side near the Vedder Mountain Road/Cultus Lake Road roundabout, and 3) an island accessible on the north side of the river in between Lickman Vedder River Parking Lot and Peach Park (had to cross a log to access the island). In contrast to the 2022 survey, only patches that were visible via the main path were recorded. Patches within the forests were not observed. Similar to 2022, visible patches were recorded in a Garmin GPS receiver, and the height, length, and width of patches were measured by use of measuring tapes. Knotweed observed within one metre was considered one patch. We noted whether the knotweed stands were isolated occurrences or in a patch. If the stands were found in a patch, the approximate number of stems per m 2 was recorded. Data Collection 2024 and 2025 Areas 1 and 2 as described for the 2023 data collection were surveyed during the summers of 2024 and 2025. For logistical reasons, area 3 was not surveyed after 2023. Because areas 1 and 2 were among the most densely populated areas by knotweed along the river, these areas provide a reliable representative indication of population change for the Vedder-Chilliwack River. Like the 2022 survey, the survey on the north side of the river included knotweed patches adjacent to the river up to the Rotary Trail, and the south side of the river was only surveyed within ten metres of the water. In 2024, the Avenza Maps app was utilized to track GPS coordinates for every visible knotweed stand or patch. In 2025, the UTM coordinates of the knotweed patches along the river were recorded by use of Garmin GPS receivers. Analyses Post collection spatial analysis was conducted using ArcGIS Pro version 2.9. Waypoint coordinates collected during field surveys were converted into point data layers within ArcGIS Pro. Attributes of each patch were joined to the corresponding point features, enabling further spatial analysis. A one-metre buffer was created around coordinates from knotweed patches observed in 2023/2024. The ‘dissolve by boundary’ and ‘feature to point’ tools were then applied to merge overlapping points within one metre. Two-metre buffers were then generated around the 2023/2024 points, and 2022 coordinates that intersected within those buffers were analyzed. This comparison aimed to record patch size changes between the years, identify which patches persisted, and estimate the extent of new population growth. Excel was utilized to create height distribution histograms and create a percent frequency graph. Google Earth Pro was utilized to view and highlight the course of the river in 2021 (before the flood) and 2022 (after the flood). A proximity cluster analysis was performed which resulted in all knotweed patches within 10 m of another patch being clustered together. This allowed for the visualization and quantification of all knotweed patches which were greater than 10 m from any other patches, and thereby more likely to have been established by processes other than the natural growth of knotweed. A two-sample Kolmogorov-Smirnov test was used to compare the class size distributions of knotweed patches between the main channel of the Vedder-Chilliwack River and its tributaries to assesses whether the two samples are drawn from the same underlying distribution. Results Main Channel – 2022 In 2019, a survey by Morrow BioScience Ltd. identified 341 knotweed patches along the main channel of the river through ground surveys conducted by foot and boat access (Morrow BioScience 2025). In 2022, 1,690 knotweed patches were observed within the same stretch of the river from the Great Blue Heron Nature Reserve to the Tamihi Rapids within the Tamihi Creek Campground (Fig. 3 ). In many cases the patches overlapped between 2019 and 2022 meaning it was the same patch, but clearly there were areas where new patches had arisen since 2019 and other areas where the patches from 2019 no longer existed because of changes in the river’s course during the flood (Fig. 4 ). The majority of the knotweed surveyed in 2022 were single-stemmed individual plants, and only 16.2% were observed as a patch, meaning they were growing in clusters of multiple stems growing in close proximity to one another. Most knotweed patches found along the Vedder-Chilliwack River were less than 40 cm in height and large well-established patches accounted for less than 25% of total patches. The frequency of knotweed patches decreased as patch size increased (Fig. 5). Knotweed was frequently observed growing amongst wood debris after the flood event (Fig. 6 ). Though whether the origin of a patch was from seed germination or rhizome fragments was not discerned for each patch, the majority appeared to be growing from rhizomes. In patches growing among wood debris, the rhizomes were often visible, making it clear how the plants were spreading. Tributaries A total of ten tributaries were surveyed in the upstream region of the study area on the Vedder-Chilliwack River in 2022. Knotweed patches were found growing along six of the ten surveyed tributaries (Fig. 7 ). None of the tributaries with confluences on the southern bank of the Vedder-Chilliwack River contained knotweed, and the easternmost tributary was also knotweed-free. Knotweed is no longer present along roads in the area due to effective control efforts, suggesting that spread is now occurring primarily via fluvial transport rather than roadside spread. The Tamihi Rapids area was the first location where knotweed was observed along the river, making it the likely upstream source (pers. comm. Kathy Ma Green, Fraser Valley Invasive Species Society). The class size distribution of knotweed found in tributaries was markedly different from that in the main channel of the Vedder-Chilliwack River. In the tributaries, the majority of knotweed patches were large, well-established, and expansive (Fig. 8 ). Main Channel and Tributary Comparison The results of the Kolmogorov-Smirnov test are shown in Table 1 . As the D calc value is greater than the D crit value, there was a statistically significant difference between the distributions of knotweed size patches between the Vedder-Chilliwack River and its tributaries (P < 0.05). Table 1 Kolmogorov-Smirnov test results comparing the size class distribution of knotweed patches in the Vedder-Chilliwack River versus its tributaries revealed a D statistic of 1.95, which exceeded the critical D value of 0.19 at a significance level of 0.05. The five size classes were: (1) single shoot—less than 50 cm, (2) less than five shoots—less than 100 cm, (3) 5–10 shoots—greater than 100 cm, (4) 10–20 shoots—greater than 200 cm, and (5) more than 20 shoots—greater than 200 cm Class size Tributaries (patch %) Vedder-Chilliwack River (patch %) 1 6 43 2 8 35 3 16 11 4 30 7 5 40 4 Main Channel – 2023 to 2025 In 2023, we returned to areas that were densely concentrated with knotweed from 2022. Only patches located along pedestrian routes on both islands and the main path were chosen for examination in 2023. In areas surveyed in both 2022 and 2023, 55 patches were found in 2022, and 75% of these stands/patches survived into 2023. Out of the 112 stands/patches found in 2023, 63% arose after the 2022 survey. Sixty-six of the stands/patches had a height of 50 cm or less in 2023. Following two growing seasons since the 2022 survey, 306 additional knotweed patches were identified in 2024 that had not been observed during the initial assessment of the selected site. Within the two areas resurveyed each year, in 2024 there were 21% more patches than in 2022, and 97% more in 2025 than in 2024. By 2025, 706 knotweed patches were observed within the two Vedder-Chilliwack River sites where only 295 patches were present in 2022 (Fig. 9 ; Fig. 10 ). Discussion Nearly a five-fold increase in knotweed patches was observed in 2022 compared to 2019. In the surveyed areas, many patches persisted through two summers following the 2021 flood, and new patches continued to appear through 2023 to 2025. The November 14–15, 2021 flood drastically altered river dynamics by creating new dispersal pathways and fragmenting rhizomes with high-energy flows. Flow records from a flow station located in the Vedder-Chilliwack River show that the discharge of the river did not rise above 300 m 3 s − 1 at any point between the 2019 survey and 2022 survey, except during this flood event, when peak flows reached 719 m 3 s − 1 (Government of Canada 2023 ). This extreme flood was therefore far outside the normal hydrological regime and set the stage for the rapid expansion of knotweed. The substantial increase in knotweed patches in 2025, nearly doubling the number present in 2024, is likely linked to the major atmospheric river event that struck British Columbia’s South Coast on October 19, 2024. This event brought 89.1 mm to Chilliwack in a single day, which set a new single-day rainfall record for October 19 in the region, surpassing the previous record of 72.6 mm set in 1956 (Jussinoja 2024 ; Judd 2024 ). Although the 2024 flood was significant, it was much smaller than the November 2021 event, which produced a total of 615.6 mm in November, 257% above normal and included the new all-time single-day record rainfall of 154.6 mm on November 14, 2021 (Feinberg 2021a , b ). Extreme floods escalate bank erosion and raise the likelihood of bank failure, both of which result in increased knotweed distribution (Colleran et al. 2020 ). The 2021 flooding event changed the course of the Vedder-Chilliwack River, notably in two locations where islands formed above Eagle Lane and near Chilliwack River Provincial Park. These newly formed islands had little existing vegetation, creating ideal disturbed habitats where knotweed could establish ahead of native riparian species, contributing to much of the post-flood increase in knotweed density. Similar flood-driven establishment was documented on four Vermont river systems following Tropical Storm Irene in 2011, where channel reworking redistributed knotweed propagules and facilitated new colonies (Colleran and Goodall 2014 ). Along rivers in the Czech Republic, areas subject to flooding held more than twice as many Himalayan balsam ( Impatiens glandulifera ) (Čuda et al. 2017 ). Our findings highlight the urgency to understand and respond in a timely fashion as flooding frequency and intensity is increasing due to climate change, changing rivers and spreading many invasive plant species (O’Briain 2019, Bolpagni 2021 , Gurnell and Bertoldi 2024 ). The rhizome network connecting knotweed plants can reportedly extend up to eighteen metres in length; however, the rhizomes rarely extend more than four metres in one lateral direction from above-ground plants (Fennell et al. 2018 ). Knotweed growth in areas distant from other patches indicate that flood waters broke apart the existing rhizomes and carried the fragments to new locations. Knotweed growing within the wood debris left from the flood are representative of some of the new locations hosting knotweed growth. It is worth noting that part of the increase in knotweed since 2019 is due to regular spreading occurrences (Rouleau et al. 2023 ). In the Fraser Valley, seasonal water level fluctuations include a predictable annual spring freshet following snowmelt in the Fraser River watershed (Government of Canada 2017 ). Essentially the 2021 flood injected additional knotweed propagules into the system, exponentially increasing the cumulative spread that was already occurring more gradually during seasonal water level fluctuations. Further evidence which supports the major flood event as the primary cause of knotweed increase between 2019 and 2022 includes the large proportion of knotweed plants designated as class 1 in size, the smallest patch size designation (single shoot, < 50 cm). Well-established knotweed patches commonly grow well over 1 m in height and form dense monocultural stands (Child 1999 ). It is thus evident that the preponderance of small patches is indicative of recent establishment of patches which have not yet been able to establish an extensive underground rhizomatic system with sufficient carbohydrate stores for extensive vegetation growth (Martin 2019 ). Furthermore, the cluster analysis revealed that 11% of the knotweed patches in the Vedder-Chilliwack River were greater than 10 m from any other patches. Knotweed rhizomatic growth is known to extend a maximum of 7 m laterally without producing above-ground growth (Child and Wade 2000 ). Therefore, the presence of numerous patches, 65% of which were under 50 cm in height, located over 10 m from any other patches indicates that these were not formed through the natural rhizomatic growth of established knotweed. The most plausible explanation is that the flood event was responsible for breaking off and transporting rhizome fragments throughout the river, and these are the lone stands observed in this survey (Cottet et al. 2020 ; Matte et el. 2021). This is further substantiated by the frequent observations we made of knotweed growing from flood debris. While the extent of the phenomenon was not quantified, it was observed commonly throughout the surveyed area. With extensive knotweed populations in the tributaries we surveyed, it is highly likely that knotweed in these streams regularly spread to the Vedder-Chilliwack River itself. These surveys specifically provided insights about the possible chief contributors of knotweed to the Vedder-Chilliwack River and allow for the implementation of source-based management. Bell Brook and Ryder Creek exhibited the greatest invasion of knotweed. Additionally, two unnamed tributaries near Edwards Road were found to have considerable knotweed populations. Interestingly, all of the tributaries which were found to have become infested with knotweed were located on the North side of the Vedder-Chilliwack River. The two surveyed tributaries on the South side of the river did not exhibit any knotweed. The North side of the Vedder-Chilliwack River is considerably more developed and has a much higher level of human population and traffic, indicating a possible correlation between knotweed presence and human activity (Martin 2019 ). A likely scenario is that knotweed originally invaded the watershed in this area via roadsides. This pathway has now been closed off due to extensive control of knotweed on roadsides and other inland areas (Kathy Ma Green, Executive Director, Fraser Valley Invasive Species Society, pers. comm.). Similar combinations of human disturbance and roadside and river dispersion have been seen in other areas invaded by knotweed (Duquette et al. 2016 ; Charpentier et al. 2024 ). A comparison of knotweed population distributions between the Vedder-Chilliwack River and its tributaries revealed a significant difference in size distribution. A greater proportion of the knotweed found in tributaries was designated as class 4 (10 to 20 shoots, > 200 cm) or class 5 (> 20 shoots, > 200 cm). These large patches indicate that they have been established for years and were not drastically affected by the flood event. Contrastingly, within the Vedder-Chilliwack River, there was a greater proportion of knotweed patches categorized as class size 1 (single shoot, < 50 cm) or 2 (< 5 shoots, < 100 cm). Therefore, it can be assumed that a substantial portion of the knotweed spread in the Vedder-Chilliwack River watershed likely originates from established patches in tributaries as seen in river systems in Québec (Matte et al. 2021 ). The present study has shown that specific tributaries could be likely sources for the knotweed in the Vedder-Chilliwack River, specifically Ryder Creek, Bell Brook, and the unnamed tributaries 3 and 4. Therefore, the control of knotweed along these tributaries is of particular importance. Rouleau et al. ( 2023 ) recommend targeting juvenile knotweed individuals to slow knotweed invasion when knotweed distribution is not yet abundant. They propose that manually removing newly distributed rhizome fragments before they establish networks can greatly limit knotweed growth, and that it is extremely cost effective. Management efforts, through chemical or manual control as per Rouleau et al. ( 2023 ), could be implemented in the growing season immediately following a major flood event like that of 2021 to greatly curtail future population increases. Unfortunately, since no immediate measures were taken in this case, knotweed stands increased five-fold in the initial year and continued to increase in subsequent years. Not every flood-dispersed stand survived, but the number of knotweed patches on the river continues to increase exponentially. Climate change supports population growth of invasive species as an increase in extreme weather events cause native species to lose their natural advantages and give invasive species room to take over (Finch et al. 2021 ). Elevated atmospheric CO 2 levels can enhance CO 2 uptake by plants, increasing herbicide resistance (Ziska et al. 2009 ). This is problematic for management as herbicides are the most effective treatment for many invasive plants, including knotweed. Changes in temperature and humidity can make environments more favourable for invasive species (Clements and Jones 2021 ). Groeneveld et al. ( 2014 ) demonstrated that sexual reproduction of Japanese knotweed is occurring at its northern distribution limit in Québec, providing evidence that climate warming is enhancing the reproductive capacity of this species in previously inhospitable regions. While southern Patagonia remains mostly inhospitable for the moment (Lacy et al. 2021 ), the plant already has a foothold in South America as well (Saldaña et al. 2009 ; Fuentes et al. 2011 ). Lavoie ( 2017 ) similarly emphasizes the widespread ecological impacts of invasive knotweeds, including their ability to alter soil chemistry, reduce native biodiversity, and degrade riparian habitats. Climate change both allows this plant to spread and persist in novel environments and then provides a means of exponential spreads via disastrous floods. Knotweed control is thus a means of creating resilience to extreme flooding. River course changes from flooding events can open new dispersal routes for knotweed, and with extreme flooding expected to become more frequent under a changing climate in North America (Gillett et al. 2022 ), such events accelerate its spread. The patterns observed on the Vedder-Chilliwack River mirror findings from other river systems. In Vermont, USA, Colleran and Goodall ( 2014 ) documented that flooding events distributed Japanese knotweed propagules across floodplains, with fragments retaining viability for over a year, leading to widespread establishment of new plants. In Québec, Canada, Matte et al. ( 2021 ) found that riverbanks with Japanese knotweed experienced significantly more erosion following a major flood compared to those without, highlighting the plant’s role in destabilizing riverbanks during flood events. Similarly, in eastern US, Colleran et al. ( 2020 ) demonstrated that knotweed displaces native deep-rooted vegetation and weakens soil structure, which increases vulnerability to erosion during high-flow events. Likewise, Rouleau et al. ( 2023 ) in Québec reported that floods and ice flows in Canadian rivers uproot knotweed rhizomes, facilitating their downstream spread. These findings from diverse regions align with our observations from the Vedder-Chilliwack River. Flooding has repeatedly been identified as a powerful driver of invasive species establishment in riparian ecosystems. Fluvial disturbance creates bare, nutrient-rich substrates that are highly vulnerable to colonization. Invasive giant hogweed ( Heracleum mantegazzianum ) and reed canary grass ( Phalaris arundinacea ) have been shown to capitalize on flood-created disturbance zones in European and North American rivers (Kercher and Zedler 2004a ; 2004b ; Trottier et al. 2017 ). Extreme floods are likely to accelerate not only the spread of knotweed but also a suite of other invasive riparian species. As climate change intensifies the frequency and magnitude of floods, our findings offer insight into how invasive species increases may accelerate through geomorphic disturbance. Declarations Funding This work was financially supported by the Natural Sciences and Engineering Research Council of Canada Discovery Development Grant (DDG-2022-00017) to DRC, Natural Sciences and Engineering Research Council of Canada Undergraduate Student Research awards to SD and JB, Weed Science Society of America undergraduate research awards to AA, SD, LM, and JB, and by Trinity Western University. Competing Interests The authors have no relevant financial or non-financial interests to disclose. Author Contributions DRC developed the study’s conception and all authors contributed to the study design. Data collection was performed by SD, AA, JB, and LM. Analysis and mapping were performed by SD, AA, and JB. The first draft of the manuscript was written by SD, and all authors commented on subsequent versions of the manuscript. All authors read and approved the final manuscript. Acknowledgements We thank Hannah Munnalall, Alexis Graves, Jadon Deffenbaugh, Megumi Metcalfe, Jihyun Lee, Melissa Graves, Benett ImBeau, and Maia Olson for their assistance in the field surveying. Special thanks to Kathy Ma Green from Fraser Valley Invasive Species Society for her field data collection advice. We acknowledge Brian Colleran for helpful comments on a previous version of the manuscript. We are grateful for funding support from the Natural Sciences and Engineering Research Council of Canada, the Weed Science Society of America, and Trinity Western University. References Aguilera AG, Alpert P, Dukes JS, Harrington R (2009) Impacts of the invasive plant Fallopia japonica (Houtt.) on plant communities and ecosystem processes. Biol Invasions 12:1243–1252. https://doi-org.twu.idm.oclc .org/10.1007/s10530-009-9543-z Anatskaya OV, Vinogradov AE (2022) Polyploidy as a fundamental phenomenon in evolution, development, adaptation and diseases. 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The length of the river that was surveyed in 2022 extends from the Great Blue Heron Nature Reserve to Tamihi Creek Campground (boundaries marked in red). Image produced via Google Earth (2022)\u003c/p\u003e","description":"","filename":"Picture1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7456717/v1/39d0bda9f5a19d270d67bd28.jpg"},{"id":90617586,"identity":"443cb86c-88d8-49cd-98fd-ca8c4ce4ecc6","added_by":"auto","created_at":"2025-09-04 19:07:22","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":217593,"visible":true,"origin":"","legend":"\u003cp\u003eKnotweed patches surveyed in the summer of 2022 displaying a range of patch class size designations: class 1 (top left), class 3 (right), and class 5 (bottom left)\u003c/p\u003e","description":"","filename":"Picture2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7456717/v1/86c2745ca7755cbca7f07661.jpg"},{"id":90618874,"identity":"04095fb3-65f2-400c-a378-810839639185","added_by":"auto","created_at":"2025-09-04 19:31:22","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":72627,"visible":true,"origin":"","legend":"\u003cp\u003eMap of knotweed patches at the Vedder-Chilliwack River surveyed in 2019 compared to 2022. All patches were located between the Great Blue Heron Nature Reserve and the Tamihi Creek Campground. Hatched areas indicate sites not surveyed in 2022 due to private property access restrictions and inaccessibility following the flood event\u003c/p\u003e","description":"","filename":"Picture3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7456717/v1/c10461e4278e6c148a8a5fbe.jpg"},{"id":90617590,"identity":"49db8c9a-5b3c-478a-985f-97aee2b61de5","added_by":"auto","created_at":"2025-09-04 19:07:22","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":150326,"visible":true,"origin":"","legend":"\u003cp\u003eObservable Vedder-Chilliwack River course differences above Eagle Lane between \u003cstrong\u003eA)\u003c/strong\u003e 2021 before the Pacific Northwest flood and \u003cstrong\u003eB)\u003c/strong\u003e 2022 after the flood, and near Chilliwack River Provincial Park between \u003cstrong\u003eC)\u003c/strong\u003e2021 before the flood and \u003cstrong\u003eD)\u003c/strong\u003e 2022 after the flood. This figure was created with the Historical Imagery feature on Google Earth Pro. The polygon tool was utilized to trace the river boundaries and islands in 2021 and 2022\u003c/p\u003e","description":"","filename":"Picture4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7456717/v1/47121fd84bdf6ef447725328.jpg"},{"id":90618426,"identity":"9bbc471f-a98f-4107-9417-18dd5381f60c","added_by":"auto","created_at":"2025-09-04 19:23:22","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":73743,"visible":true,"origin":"","legend":"\u003cp\u003eKnotweed class size frequency in the Vedder-Chilliwack River mainstem in 2022. The five size classes were: (1) single shoot—less than 50 cm, (2) less than five shoots—less than 100 cm, (3) 5 – 10 shoots—greater than 100 cm, (4) 10 – 20 shoots—greater than 200 cm, and (5) more than 20 shoots—greater than 200 cm\u003c/p\u003e","description":"","filename":"Picture5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7456717/v1/05a3b0ba8808eb033f8b5735.jpg"},{"id":90618427,"identity":"b47966a6-8268-40d3-ab37-08bc9c2ddb03","added_by":"auto","created_at":"2025-09-04 19:23:22","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":312973,"visible":true,"origin":"","legend":"\u003cp\u003eKnotweed stands growing amongst wood debris\u003cstrong\u003e \u003c/strong\u003ein the Vedder-Chilliwack River in the summer of 2022\u003c/p\u003e","description":"","filename":"Picture6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7456717/v1/5f7eaddf256cb488c85f4ba4.jpg"},{"id":90617595,"identity":"fb21884f-c2dc-41cf-b9cd-c3d6c882c099","added_by":"auto","created_at":"2025-09-04 19:07:22","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":106899,"visible":true,"origin":"","legend":"\u003cp\u003eTributaries of the Vedder-Chilliwack River surveyed for knotweed in summer 2022. Ryder Creek shown in detail\u003c/p\u003e","description":"","filename":"Picture7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7456717/v1/34589d4d82baa8b16f021deb.jpg"},{"id":90617593,"identity":"3b9fe673-acd6-4e18-a6f5-da08fcc49996","added_by":"auto","created_at":"2025-09-04 19:07:22","extension":"jpg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":63467,"visible":true,"origin":"","legend":"\u003cp\u003eSize class distribution of knotweed patches across all tributaries. The five size classes were: (1) single shoot—less than 50 cm, (2) less than five shoots—less than 100 cm, (3) 5 – 10 shoots—greater than 100 cm, (4) 10 – 20 shoots—greater than 200 cm, and (5) more than 20 shoots—greater than 200 cm\u003c/p\u003e","description":"","filename":"Picture8.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7456717/v1/efa64fa96c64d5216bf42abc.jpg"},{"id":90618107,"identity":"1e44cd7f-6e24-4235-967d-ca48fa656a4f","added_by":"auto","created_at":"2025-09-04 19:15:22","extension":"jpg","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":318718,"visible":true,"origin":"","legend":"\u003cp\u003eMap of knotweed patches at the Vedder-Chilliwack River surveyed in 2025 compared to 2022. In 2025, all patches were found \u003cstrong\u003eA)\u003c/strong\u003e on the north side of the river near the Great Blue Heron Nature Reserve and \u003cstrong\u003eB)\u003c/strong\u003e on the south side of the river near the Vedder Mountain Road/Cultus Lake Road roundabout\u003c/p\u003e","description":"","filename":"Picture9.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7456717/v1/fbe4566cb1301e94937c65a2.jpg"},{"id":90617598,"identity":"f9eeab5f-fa30-48f2-850b-849ab1ec96b7","added_by":"auto","created_at":"2025-09-04 19:07:22","extension":"jpg","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":242238,"visible":true,"origin":"","legend":"\u003cp\u003eMap comparing locations of knotweed patches surveyed in 2024 and 2025 along the Vedder-Chilliwack River\u003c/p\u003e","description":"","filename":"Picture10.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7456717/v1/4463a5dbbdaa240a573c68c6.jpg"},{"id":99545432,"identity":"18e419b1-b926-4139-8e23-4714590984c5","added_by":"auto","created_at":"2026-01-05 16:07:29","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2374498,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7456717/v1/b817bfc5-c45f-49da-a1cc-075ee775dffd.pdf"}],"financialInterests":"","formattedTitle":"Implications of extreme flooding events modifying fluvial geomorphology for dispersal of knotweed (Reynoutria spp.) in the wake of climate change","fulltext":[{"header":"Introduction","content":"\u003cp\u003eJapanese knotweed (\u003cem\u003eReynoutria japonica\u003c/em\u003e) and giant knotweed (\u003cem\u003eReynoutria sachalinensis\u003c/em\u003e), both members of the Polygonaceae family, are herbaceous perennials native to East Asia including Japan, Korea, and parts of China (Drazan et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Knotweeds were introduced to North America in the late nineteenth century as ornamental plants (Barney \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). Knotweed had already been introduced to Europe earlier in the nineteenth century, also as a prize-winning ornamental plant which initially commanded large sums of money (Bailey and Conolly \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2000\u003c/span\u003e). In both North America and Europe, a hybrid of Japanese and giant knotweed forms referred to as Bohemian knotweed (\u003cem\u003eReynoutria\u003c/em\u003e \u0026times; \u003cem\u003ebohemica\u003c/em\u003e) occurs which is also very invasive (Neupert et al. \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Knotweeds are now recognized as among the world\u0026rsquo;s most invasive species due to their strong competitive and dispersal abilities, which allow them to rapidly form dense patches that displace native vegetation and are extremely difficult to remove (Gillies et al. \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). They outcompete native vegetation by blocking sunlight and releasing allelopathic compounds, which are chemicals that inhibit the growth of surrounding vegetation (Gillies et al. \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). While hybrid populations (\u003cem\u003eR.\u003c/em\u003e \u0026times; \u003cem\u003ebohemica\u003c/em\u003e) produce viable seeds, \u003cem\u003eR. japonica\u003c/em\u003e regenerates almost exclusively from rhizomes because the introduced biotypes produce very little pollen (Barney et al. 2006; Smith et al. \u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Gillies et al. \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Here we will refer to \u003cem\u003eReynoutria\u003c/em\u003e spp. as \u0026ldquo;knotweed\u0026rdquo; because all three related taxa coexist in many parts of North America, including on the west coast.\u003c/p\u003e\u003cp\u003eKnotweed species are a high priority for management in Europe and North America including the Pacific Northwest region of North America specifically because they pose serious threats to ecosystem health and human infrastructure (Gaskin et al. \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Gillies et al. \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). All three \u003cem\u003eReynoutria\u003c/em\u003e species have been listed as Noxious Weeds under British Columbia\u0026rsquo;s Weed Control Regulation (Government of British Columbia \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Both Oregon and Washington classify knotweed as Class B noxious weeds, meaning that they require control in locations where not yet widespread (Washington State Noxious Weed Control Board \u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e1995\u003c/span\u003e; Oregon Department of Agriculture \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Knotweed is also listed on the Pacific Northwest states\u0026rsquo; quarantine lists; therefore, transport and distribution of knotweed plant parts is prohibited. These legislative measures reflect the shared recognition across the Pacific Northwest that knotweed poses a severe and ongoing threat. Knotweed has spread extensively through human activity and now climate-induced floods and has a reputation for damaging infrastructure and undermining riverbank stability (Colleran et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Matte et al. \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Kaehler \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Excavating knotweed is generally not a successful eradication method due to the regenerative nature of knotweed, unless from tiny fragments in an EDRR context (Colleran and Goodall \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2014\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). For mature plants, successful excavation must include the area surrounding a patch of knotweed as the rhizomes can extend at least ten metres from the parent plant or more (Child and Wade \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2000\u003c/span\u003e; Fennel et al. 2018). Herbicides are regarded as the only consistently effective methodology against knotweed growth; however, they are prohibited for use in many environmental regions in British Columbia such as along waterways (BC Ministry of Environment 2016).\u003c/p\u003e\u003cp\u003eA major reason to seek effective management and/or eradication strategies is that beyond risks to the built environment, knotweed facilitates riverbank erosion (Arnold and Toran 2018; Hammer 2019; Matte 2021; Kaehler \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Penn 2024), presumably because the rhizome-dominated underground portion of the plant lacks root hairs, and therefore does not bind to the soil. Additionally, the rhizomes are concentrated in the surface layer, under which there are many fewer rhizomes. Having eliminated the variety of depth and form that the displaced floral species provided, no vegetation remains to bind the soil (Child et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e1992\u003c/span\u003e; Aguilera et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). Furthermore, mycorrhizae are reduced by knotweed allelochemicals (Kato-Noguchi \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), which would weaken yet another aspect of soil cohesion.\u003c/p\u003e\u003cp\u003eGrowth can occur from very small rhizome and stem fragments that include at least one node (De Waal \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2001\u003c/span\u003e; S\u0026aacute;sik and Pavol \u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). Roadways frequently become infested with knotweed as activities such as mowing can transfer rhizome and stem fragments to new locations. Knotweed grows abundantly near waterways as stem and rhizome fragments, as well as seeds, can spread through rivers due to their buoyant nature (Rouifed et al. \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Drazan 2021). Similarly, flooding encourages the growth of knotweed as plant fragments are brought downstream to then form new stands. Colleran and Goodall (\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2014\u003c/span\u003e) found that following a flooding event in Vermont, 70% of new knotweed plants originated from rhizome fragments, while 30% originated from stem fragments. By contrast Rouleau et al. (\u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e2023\u003c/span\u003e) observed that all the new plants were sourced from rhizome fragments following flooding in Qu\u0026eacute;bec.\u003c/p\u003e\u003cp\u003eInvasive species tolerate a broader spectrum of environmental conditions than native species (Flanagan et al. \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Not only does climate change make ecosystems more susceptible to invasive plants, but invasive plants worsen climate change impacts on ecosystems (Mainka and Howard \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2010\u003c/span\u003e). Riparian ecosystems are key points for climate and invasive species interactions (Flanagan et al. \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Climate change and invasive species interact synergistically, with climate change promoting evolution of invasive plants (Ziska et al. \u003cspan citationid=\"CR68\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Clements and Jones \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Knotweed is very adaptable. At least six major mechanisms promote rapid knotweed evolution: polyploidy, hybridization, local adaptation, clonal growth, phenotypic plasticity, and epigenetics (Clements and Jones \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Polyploidy and hybridization facilitate knotweed\u0026rsquo;s tolerance across a relatively broad range of ecological conditions (Clements and Jones \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Anatskaya and Vinogradov \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Local adaptation refers to knotweed\u0026rsquo;s ability to adjust to specific environmental conditions, while clonal growth occurs through vegetative propagation via extensive rhizome networks (Clements and Jones \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Knotweed exhibits phenotypic plasticity, with genotypes capable of producing a range of phenotypes in response to varying environmental conditions (Clements and Jones \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Flexibility in gene expression via epigenetics enables quick adjustments by knotweed to environmental stressors, making epigenetic effects advantageous for knotweed invasion (Jones \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Asensi-Fabado et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Clements and Jones \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Knotweeds utilize these six mechanisms differently depending on environmental circumstances, making them more adaptable to extreme environmental conditions compared to native vegetation (Parepa et al. \u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Duquette et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Gillies et al. \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Clements and Jones \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eThe November 2021 Pacific Northwest floods prompted a state of emergency for British Columbia (Zussman \u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Slide damage, bridge collapses, and floodwaters were recorded across southwestern British Columbia in Merritt, Abbotsford, Princeton, and Chilliwack (Gillett et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Due to human-induced climate change, the probability of an atmospheric river that generated the intense rainfall experienced during the 2021 event increased by more than 60% since the pre-industrial climate; what was once a 1 in 20.7-year event is now calculated to be a 1 in 11.8-year event (Gillett et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). The high precipitation was the primary contributor to the extreme streamflow, but snowmelt from the rapid temperature rise during the 2021 heavy rainfall event also made a significant contribution (Gillett et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). This natural disaster was the most expensive in British Columbia\u0026rsquo;s history (Gillett et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), and many factors, such as the potential spread of invasive plants due to the floods, have yet to be accounted for in the cost analysis.\u003c/p\u003e\u003cp\u003eFluvial geomorphology and invasive plant spread are closely connected (Wieting et al. \u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Hardwick et al. \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). Along the Vedder-Chilliwack River, the sheer force of the floodwaters not only eroded riverbanks but also uprooted trees, carrying them downstream where they accumulated on islands. In several locations, bank collapse and sediment redistribution altered the river\u0026rsquo;s shape and course. Given the abundance of knotweed in the riparian zone, it would not be surprising if dispersal of knotweed would be enhanced. Such hydrologic and geomorphic disturbances can accelerate the spread of invasive riparian plants by both transporting propagules and creating disturbed habitats favourable for colonization (Wieting et al. \u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Hardwick et al. \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2025\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eWithin the past 50 years there have been occasional instances of discharge levels in the Vedder-Chilliwack River above 500m\u003csup\u003e3\u003c/sup\u003es\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, which correspond to the times of most intense flooding (Ham and Church \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2000\u003c/span\u003e). On November 15th, 2021, the Vedder-Chilliwack River experienced a discharge of over 700 m\u003csup\u003e3\u003c/sup\u003es\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u0026mdash;ten times greater than the mean. This resulted in significant flooding and erosion of the stream banks throughout the river (Government of Canada \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). This provided an opportunity to study the effects of extreme flood events on knotweed dispersal in waterways.\u003c/p\u003e\u003cp\u003eOur objectives in this study were to 1) evaluate the population increase and spread of knotweed in the Vedder-Chilliwack River following the extreme flooding event in November 2021, to 2) examine whether particular tributaries were disproportionately responsible for the knotweed spread during flooding, and 3) evaluate the role of alteration of fluvial morphology on invasive plant spread during extreme flooding to help design proactive measures to prevent the spread of invasives under climate change.\u003c/p\u003e"},{"header":"Materials and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003eSite Description\u003c/h2\u003e\u003cp\u003eThe Vedder-Chilliwack River is over ninety-five kilometres long and flows northwest from its headwaters in northern Washington, USA and empties into the Fraser River in British Columbia, Canada (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Near the source of the river in Washington State are kilometres of old-growth forests within the North Cascades National Park. Contrastingly, the portion of the river extending from Chilliwack Lake to the Fraser River is bordered by second-growth forests which have been heavily logged since the beginning of the 19th century (Cleary \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2001\u003c/span\u003e). This logging has had detrimental impacts on the health of this stream by both decreasing stream complexity and increasing erosional risk (Ogston et al. \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e2015\u003c/span\u003e).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eChilliwack Lake represents a convenient boundary for the purposes of this study, by effectively separating the upstream American portion of the Vedder-Chilliwack River from the downstream Canadian portion. The hydrologic transportation processes are arrested at the lake, thus causing unique hydrology upstream and downstream of the lake (Ham and Church \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2000\u003c/span\u003e). This current study focused on the Vedder-Chilliwack River downstream of Chilliwack Lake from the Tamihi Rapids to Great Blue Heron Park where the vast majority of knotweed patches on the river occur (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). This portion of the river is characterized as being a high-powered stream with bankfull width ranging from 40 m to 80 m, and a boulder/cobble dominant stream bed (Ogston et al. \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). The average annual discharge in this portion of the stream is 60 m\u003csup\u003e3\u003c/sup\u003es\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (Ham and Church \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2000\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eThe Vedder-Chilliwack River is a very popular recreational fishing stream, and the river supports a large freshwater sport fishery. Although the river has the two names with the Vedder being the lower portion of the river below the Vedder Crossing Bridge, it will be referred to as the Vedder-Chilliwack River within this paper. Several salmon species migrate into Chilliwack including Chinook, Chum, Pink, Sockeye, and Coho; however, most spawning is restricted to nearby tributaries as mainstem upstream spawning habitat is limited (City of Chilliwack n.d.; Ogston et al. \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Various types of trout, such as rainbow, steelhead, and coastal cutthroat also make the Vedder-Chilliwack River their home (Tourism Chilliwack \u003cspan citationid=\"CR63\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). This river was recommended as a prime study site by the Fraser Valley Invasive Species Society due to concerns about the abundance of knotweed and the difficulty of controlling it in the Vedder-Chilliwack watershed.\u003c/p\u003e\u003c/div\u003e\n\u003ch3\u003eData Collection 2022\u003c/h3\u003e\n\u003cp\u003eData collection occurred through field surveys of the Vedder-Chilliwack River. From July 4 to August 23, the UTM coordinates of the knotweed patches along the river were recorded by use of two Garmin GPS receivers. The presence or absence of dead stems as well as size, including height, width, and length, were recorded for each patch (by use of measuring tapes). ArcGIS Survey123 was used for recording data and measurements. The heights of tall knotweed patches were measured via Suunto PM-5/1520 clinometers. Surveying efforts were designed to capture as much of the knotweed population as possible, within the constraints of site accessibility. The extent of surveying along the mainstem was based on knowledge of the extent of the infestation, so even though the whole river was not surveyed, very little knotweed occurs outside the surveyed area. On the north side of the Vedder-Chilliwack River, surveys included all knotweed patches located adjacent to the river. All knotweed patches on islands were surveyed in their entirety. On the south side of the river, accessibility was more limited due to private property and dense vegetation. As a result, surveys on the south side were restricted to areas within ten metres of the riverbank. Additionally, ten tributaries were surveyed which had confluences upstream of the Vedder Bridge and downstream of the Tamihi Creek Campground. The wetted width was approximated to form the extent of the surveyed area for each surveyed tributary.\u003c/p\u003e\u003cp\u003eKnotweed patches found alongside tributaries were assigned to a size class. The five size classes were: (1) single shoot\u0026mdash;less than 50 cm, (2) less than five shoots\u0026mdash;less than 100 cm, (3) 5\u0026ndash;10 shoots\u0026mdash;greater than 100 cm, (4) 10\u0026ndash;20 shoots\u0026mdash;greater than 200 cm, and (5) more than 20 shoots\u0026mdash;greater than 200 cm (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). These class sizes were modified from the Invasive Alien Plant Program (IAPP) standards and made applicable for knotweed (Kathy Ma Green, Executive Director of the Fraser Valley Invasive Species Society, pers. comm.).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\n\u003ch3\u003eData Collection 2023\u003c/h3\u003e\n\u003cp\u003eIn the summer of 2023, we revisited areas that were densely populated with knotweed patches, which accounted for roughly 20% of the total area surveyed in 2022 to obtain a representative indication of population change since 2022. The areas surveyed in 2023 were 1) on the north side of the river near Great Blue Heron Nature Reserve, 2) on the south side near the Vedder Mountain Road/Cultus Lake Road roundabout, and 3) an island accessible on the north side of the river in between Lickman Vedder River Parking Lot and Peach Park (had to cross a log to access the island). In contrast to the 2022 survey, only patches that were visible via the main path were recorded. Patches within the forests were not observed. Similar to 2022, visible patches were recorded in a Garmin GPS receiver, and the height, length, and width of patches were measured by use of measuring tapes. Knotweed observed within one metre was considered one patch. We noted whether the knotweed stands were isolated occurrences or in a patch. If the stands were found in a patch, the approximate number of stems per m\u003csup\u003e2\u003c/sup\u003e was recorded.\u003c/p\u003e\n\u003ch3\u003eData Collection 2024 and 2025\u003c/h3\u003e\n\u003cp\u003eAreas 1 and 2 as described for the 2023 data collection were surveyed during the summers of 2024 and 2025. For logistical reasons, area 3 was not surveyed after 2023. Because areas 1 and 2 were among the most densely populated areas by knotweed along the river, these areas provide a reliable representative indication of population change for the Vedder-Chilliwack River. Like the 2022 survey, the survey on the north side of the river included knotweed patches adjacent to the river up to the Rotary Trail, and the south side of the river was only surveyed within ten metres of the water. In 2024, the Avenza Maps app was utilized to track GPS coordinates for every visible knotweed stand or patch. In 2025, the UTM coordinates of the knotweed patches along the river were recorded by use of Garmin GPS receivers.\u003c/p\u003e\n\u003ch3\u003eAnalyses\u003c/h3\u003e\n\u003cp\u003ePost collection spatial analysis was conducted using ArcGIS Pro version 2.9. Waypoint coordinates collected during field surveys were converted into point data layers within ArcGIS Pro. Attributes of each patch were joined to the corresponding point features, enabling further spatial analysis. A one-metre buffer was created around coordinates from knotweed patches observed in 2023/2024. The \u0026lsquo;dissolve by boundary\u0026rsquo; and \u0026lsquo;feature to point\u0026rsquo; tools were then applied to merge overlapping points within one metre. Two-metre buffers were then generated around the 2023/2024 points, and 2022 coordinates that intersected within those buffers were analyzed. This comparison aimed to record patch size changes between the years, identify which patches persisted, and estimate the extent of new population growth.\u003c/p\u003e\u003cp\u003eExcel was utilized to create height distribution histograms and create a percent frequency graph. Google Earth Pro was utilized to view and highlight the course of the river in 2021 (before the flood) and 2022 (after the flood). A proximity cluster analysis was performed which resulted in all knotweed patches within 10 m of another patch being clustered together. This allowed for the visualization and quantification of all knotweed patches which were greater than 10 m from any other patches, and thereby more likely to have been established by processes other than the natural growth of knotweed. A two-sample Kolmogorov-Smirnov test was used to compare the class size distributions of knotweed patches between the main channel of the Vedder-Chilliwack River and its tributaries to assesses whether the two samples are drawn from the same underlying distribution.\u003c/p\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\u003ch2\u003eMain Channel \u0026ndash; 2022\u003c/h2\u003e\u003cp\u003eIn 2019, a survey by Morrow BioScience Ltd. identified 341 knotweed patches along the main channel of the river through ground surveys conducted by foot and boat access (Morrow BioScience 2025). In 2022, 1,690 knotweed patches were observed within the same stretch of the river from the Great Blue Heron Nature Reserve to the Tamihi Rapids within the Tamihi Creek Campground (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). In many cases the patches overlapped between 2019 and 2022 meaning it was the same patch, but clearly there were areas where new patches had arisen since 2019 and other areas where the patches from 2019 no longer existed because of changes in the river\u0026rsquo;s course during the flood (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). The majority of the knotweed surveyed in 2022 were single-stemmed individual plants, and only 16.2% were observed as a patch, meaning they were growing in clusters of multiple stems growing in close proximity to one another.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eMost knotweed patches found along the Vedder-Chilliwack River were less than 40 cm in height and large well-established patches accounted for less than 25% of total patches. The frequency of knotweed patches decreased as patch size increased (Fig.\u0026nbsp;5).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eKnotweed was frequently observed growing amongst wood debris after the flood event (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e6\u003c/span\u003e). Though whether the origin of a patch was from seed germination or rhizome fragments was not discerned for each patch, the majority appeared to be growing from rhizomes. In patches growing among wood debris, the rhizomes were often visible, making it clear how the plants were spreading.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\n\u003ch3\u003eTributaries\u003c/h3\u003e\n\u003cp\u003eA total of ten tributaries were surveyed in the upstream region of the study area on the Vedder-Chilliwack River in 2022. Knotweed patches were found growing along six of the ten surveyed tributaries (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e7\u003c/span\u003e). None of the tributaries with confluences on the southern bank of the Vedder-Chilliwack River contained knotweed, and the easternmost tributary was also knotweed-free. Knotweed is no longer present along roads in the area due to effective control efforts, suggesting that spread is now occurring primarily via fluvial transport rather than roadside spread. The Tamihi Rapids area was the first location where knotweed was observed along the river, making it the likely upstream source (pers. comm. Kathy Ma Green, Fraser Valley Invasive Species Society).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe class size distribution of knotweed found in tributaries was markedly different from that in the main channel of the Vedder-Chilliwack River. In the tributaries, the majority of knotweed patches were large, well-established, and expansive (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e8\u003c/span\u003e).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\u003ch2\u003eMain Channel and Tributary Comparison\u003c/h2\u003e\u003cp\u003eThe results of the Kolmogorov-Smirnov test are shown in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. As the D\u003csub\u003ecalc\u003c/sub\u003e value is greater than the D\u003csub\u003ecrit\u003c/sub\u003e value, there was a statistically significant difference between the distributions of knotweed size patches between the Vedder-Chilliwack River and its tributaries (P\u0026thinsp;\u0026lt;\u0026thinsp;0.05).\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eKolmogorov-Smirnov test results comparing the size class distribution of knotweed patches in the Vedder-Chilliwack River versus its tributaries revealed a D statistic of 1.95, which exceeded the critical D value of 0.19 at a significance level of 0.05. The five size classes were: (1) single shoot\u0026mdash;less than 50 cm, (2) less than five shoots\u0026mdash;less than 100 cm, (3) 5\u0026ndash;10 shoots\u0026mdash;greater than 100 cm, (4) 10\u0026ndash;20 shoots\u0026mdash;greater than 200 cm, and (5) more than 20 shoots\u0026mdash;greater than 200 cm\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"3\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eClass size\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eTributaries (patch %)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eVedder-Chilliwack River (patch %)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e43\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e35\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e16\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e11\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e30\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e7\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e40\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\u003ch2\u003eMain Channel \u0026ndash; 2023 to 2025\u003c/h2\u003e\u003cp\u003eIn 2023, we returned to areas that were densely concentrated with knotweed from 2022. Only patches located along pedestrian routes on both islands and the main path were chosen for examination in 2023. In areas surveyed in both 2022 and 2023, 55 patches were found in 2022, and 75% of these stands/patches survived into 2023. Out of the 112 stands/patches found in 2023, 63% arose after the 2022 survey. Sixty-six of the stands/patches had a height of 50 cm or less in 2023. Following two growing seasons since the 2022 survey, 306 additional knotweed patches were identified in 2024 that had not been observed during the initial assessment of the selected site. Within the two areas resurveyed each year, in 2024 there were 21% more patches than in 2022, and 97% more in 2025 than in 2024. By 2025, 706 knotweed patches were observed within the two Vedder-Chilliwack River sites where only 295 patches were present in 2022 (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e9\u003c/span\u003e; Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e10\u003c/span\u003e).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e"},{"header":"Discussion","content":"\u003cp\u003eNearly a five-fold increase in knotweed patches was observed in 2022 compared to 2019. In the surveyed areas, many patches persisted through two summers following the 2021 flood, and new patches continued to appear through 2023 to 2025. The November 14\u0026ndash;15, 2021 flood drastically altered river dynamics by creating new dispersal pathways and fragmenting rhizomes with high-energy flows. Flow records from a flow station located in the Vedder-Chilliwack River show that the discharge of the river did not rise above 300 m\u003csup\u003e3\u003c/sup\u003es\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at any point between the 2019 survey and 2022 survey, except during this flood event, when peak flows reached 719 m\u003csup\u003e3\u003c/sup\u003es\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (Government of Canada \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). This extreme flood was therefore far outside the normal hydrological regime and set the stage for the rapid expansion of knotweed.\u003c/p\u003e\u003cp\u003eThe substantial increase in knotweed patches in 2025, nearly doubling the number present in 2024, is likely linked to the major atmospheric river event that struck British Columbia\u0026rsquo;s South Coast on October 19, 2024. This event brought 89.1 mm to Chilliwack in a single day, which set a new single-day rainfall record for October 19 in the region, surpassing the previous record of 72.6 mm set in 1956 (Jussinoja \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Judd \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Although the 2024 flood was significant, it was much smaller than the November 2021 event, which produced a total of 615.6 mm in November, 257% above normal and included the new all-time single-day record rainfall of 154.6 mm on November 14, 2021 (Feinberg \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2021a\u003c/span\u003e,\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003eb\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eExtreme floods escalate bank erosion and raise the likelihood of bank failure, both of which result in increased knotweed distribution (Colleran et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). The 2021 flooding event changed the course of the Vedder-Chilliwack River, notably in two locations where islands formed above Eagle Lane and near Chilliwack River Provincial Park. These newly formed islands had little existing vegetation, creating ideal disturbed habitats where knotweed could establish ahead of native riparian species, contributing to much of the post-flood increase in knotweed density. Similar flood-driven establishment was documented on four Vermont river systems following Tropical Storm Irene in 2011, where channel reworking redistributed knotweed propagules and facilitated new colonies (Colleran and Goodall \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Along rivers in the Czech Republic, areas subject to flooding held more than twice as many Himalayan balsam (\u003cem\u003eImpatiens glandulifera\u003c/em\u003e) (Čuda et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Our findings highlight the urgency to understand and respond in a timely fashion as flooding frequency and intensity is increasing due to climate change, changing rivers and spreading many invasive plant species (O\u0026rsquo;Briain 2019, Bolpagni \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2021\u003c/span\u003e, Gurnell and Bertoldi \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2024\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eThe rhizome network connecting knotweed plants can reportedly extend up to eighteen metres in length; however, the rhizomes rarely extend more than four metres in one lateral direction from above-ground plants (Fennell et al. \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Knotweed growth in areas distant from other patches indicate that flood waters broke apart the existing rhizomes and carried the fragments to new locations. Knotweed growing within the wood debris left from the flood are representative of some of the new locations hosting knotweed growth. It is worth noting that part of the increase in knotweed since 2019 is due to regular spreading occurrences (Rouleau et al. \u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). In the Fraser Valley, seasonal water level fluctuations include a predictable annual spring freshet following snowmelt in the Fraser River watershed (Government of Canada \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Essentially the 2021 flood injected additional knotweed propagules into the system, exponentially increasing the cumulative spread that was already occurring more gradually during seasonal water level fluctuations.\u003c/p\u003e\u003cp\u003eFurther evidence which supports the major flood event as the primary cause of knotweed increase between 2019 and 2022 includes the large proportion of knotweed plants designated as class 1 in size, the smallest patch size designation (single shoot, \u0026lt;\u0026thinsp;50 cm). Well-established knotweed patches commonly grow well over 1 m in height and form dense monocultural stands (Child \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e1999\u003c/span\u003e). It is thus evident that the preponderance of small patches is indicative of recent establishment of patches which have not yet been able to establish an extensive underground rhizomatic system with sufficient carbohydrate stores for extensive vegetation growth (Martin \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eFurthermore, the cluster analysis revealed that 11% of the knotweed patches in the Vedder-Chilliwack River were greater than 10 m from any other patches. Knotweed rhizomatic growth is known to extend a maximum of 7 m laterally without producing above-ground growth (Child and Wade \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2000\u003c/span\u003e). Therefore, the presence of numerous patches, 65% of which were under 50 cm in height, located over 10 m from any other patches indicates that these were not formed through the natural rhizomatic growth of established knotweed. The most plausible explanation is that the flood event was responsible for breaking off and transporting rhizome fragments throughout the river, and these are the lone stands observed in this survey (Cottet et al. \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Matte et el. 2021). This is further substantiated by the frequent observations we made of knotweed growing from flood debris. While the extent of the phenomenon was not quantified, it was observed commonly throughout the surveyed area.\u003c/p\u003e\u003cp\u003eWith extensive knotweed populations in the tributaries we surveyed, it is highly likely that knotweed in these streams regularly spread to the Vedder-Chilliwack River itself. These surveys specifically provided insights about the possible chief contributors of knotweed to the Vedder-Chilliwack River and allow for the implementation of source-based management. Bell Brook and Ryder Creek exhibited the greatest invasion of knotweed. Additionally, two unnamed tributaries near Edwards Road were found to have considerable knotweed populations. Interestingly, all of the tributaries which were found to have become infested with knotweed were located on the North side of the Vedder-Chilliwack River. The two surveyed tributaries on the South side of the river did not exhibit any knotweed. The North side of the Vedder-Chilliwack River is considerably more developed and has a much higher level of human population and traffic, indicating a possible correlation between knotweed presence and human activity (Martin \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). A likely scenario is that knotweed originally invaded the watershed in this area via roadsides. This pathway has now been closed off due to extensive control of knotweed on roadsides and other inland areas (Kathy Ma Green, Executive Director, Fraser Valley Invasive Species Society, pers. comm.). Similar combinations of human disturbance and roadside and river dispersion have been seen in other areas invaded by knotweed (Duquette et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Charpentier et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2024\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eA comparison of knotweed population distributions between the Vedder-Chilliwack River and its tributaries revealed a significant difference in size distribution. A greater proportion of the knotweed found in tributaries was designated as class 4 (10 to 20 shoots, \u0026gt;\u0026thinsp;200 cm) or class 5 (\u0026gt;\u0026thinsp;20 shoots, \u0026gt;\u0026thinsp;200 cm). These large patches indicate that they have been established for years and were not drastically affected by the flood event. Contrastingly, within the Vedder-Chilliwack River, there was a greater proportion of knotweed patches categorized as class size 1 (single shoot, \u0026lt;\u0026thinsp;50 cm) or 2 (\u0026lt;\u0026thinsp;5 shoots, \u0026lt;\u0026thinsp;100 cm). Therefore, it can be assumed that a substantial portion of the knotweed spread in the Vedder-Chilliwack River watershed likely originates from established patches in tributaries as seen in river systems in Qu\u0026eacute;bec (Matte et al. \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eThe present study has shown that specific tributaries could be likely sources for the knotweed in the Vedder-Chilliwack River, specifically Ryder Creek, Bell Brook, and the unnamed tributaries 3 and 4. Therefore, the control of knotweed along these tributaries is of particular importance. Rouleau et al. (\u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e2023\u003c/span\u003e) recommend targeting juvenile knotweed individuals to slow knotweed invasion when knotweed distribution is not yet abundant. They propose that manually removing newly distributed rhizome fragments before they establish networks can greatly limit knotweed growth, and that it is extremely cost effective. Management efforts, through chemical or manual control as per Rouleau et al. (\u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), could be implemented in the growing season immediately following a major flood event like that of 2021 to greatly curtail future population increases. Unfortunately, since no immediate measures were taken in this case, knotweed stands increased five-fold in the initial year and continued to increase in subsequent years. Not every flood-dispersed stand survived, but the number of knotweed patches on the river continues to increase exponentially.\u003c/p\u003e\u003cp\u003eClimate change supports population growth of invasive species as an increase in extreme weather events cause native species to lose their natural advantages and give invasive species room to take over (Finch et al. \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Elevated atmospheric CO\u003csub\u003e2\u003c/sub\u003e levels can enhance CO\u003csub\u003e2\u003c/sub\u003e uptake by plants, increasing herbicide resistance (Ziska et al. \u003cspan citationid=\"CR67\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). This is problematic for management as herbicides are the most effective treatment for many invasive plants, including knotweed. Changes in temperature and humidity can make environments more favourable for invasive species (Clements and Jones \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Groeneveld et al. (\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2014\u003c/span\u003e) demonstrated that sexual reproduction of Japanese knotweed is occurring at its northern distribution limit in Qu\u0026eacute;bec, providing evidence that climate warming is enhancing the reproductive capacity of this species in previously inhospitable regions. While southern Patagonia remains mostly inhospitable for the moment (Lacy et al. \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), the plant already has a foothold in South America as well (Salda\u0026ntilde;a et al. \u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Fuentes et al. \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). Lavoie (\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2017\u003c/span\u003e) similarly emphasizes the widespread ecological impacts of invasive knotweeds, including their ability to alter soil chemistry, reduce native biodiversity, and degrade riparian habitats. Climate change both allows this plant to spread and persist in novel environments and then provides a means of exponential spreads via disastrous floods. Knotweed control is thus a means of creating resilience to extreme flooding.\u003c/p\u003e\u003cp\u003eRiver course changes from flooding events can open new dispersal routes for knotweed, and with extreme flooding expected to become more frequent under a changing climate in North America (Gillett et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), such events accelerate its spread. The patterns observed on the Vedder-Chilliwack River mirror findings from other river systems. In Vermont, USA, Colleran and Goodall (\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2014\u003c/span\u003e) documented that flooding events distributed Japanese knotweed propagules across floodplains, with fragments retaining viability for over a year, leading to widespread establishment of new plants. In Qu\u0026eacute;bec, Canada, Matte et al. (\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) found that riverbanks with Japanese knotweed experienced significantly more erosion following a major flood compared to those without, highlighting the plant\u0026rsquo;s role in destabilizing riverbanks during flood events. Similarly, in eastern US, Colleran et al. (\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) demonstrated that knotweed displaces native deep-rooted vegetation and weakens soil structure, which increases vulnerability to erosion during high-flow events. Likewise, Rouleau et al. (\u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e2023\u003c/span\u003e) in Qu\u0026eacute;bec reported that floods and ice flows in Canadian rivers uproot knotweed rhizomes, facilitating their downstream spread. These findings from diverse regions align with our observations from the Vedder-Chilliwack River.\u003c/p\u003e\u003cp\u003eFlooding has repeatedly been identified as a powerful driver of invasive species establishment in riparian ecosystems. Fluvial disturbance creates bare, nutrient-rich substrates that are highly vulnerable to colonization. Invasive giant hogweed (\u003cem\u003eHeracleum mantegazzianum\u003c/em\u003e) and reed canary grass (\u003cem\u003ePhalaris arundinacea\u003c/em\u003e) have been shown to capitalize on flood-created disturbance zones in European and North American rivers (Kercher and Zedler \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2004a\u003c/span\u003e; \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2004b\u003c/span\u003e; Trottier et al. \u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Extreme floods are likely to accelerate not only the spread of knotweed but also a suite of other invasive riparian species. As climate change intensifies the frequency and magnitude of floods, our findings offer insight into how invasive species increases may accelerate through geomorphic disturbance.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eFunding\u003c/h2\u003e\u003cp\u003eThis work was financially supported by the Natural Sciences and Engineering Research Council of Canada Discovery Development Grant (DDG-2022-00017) to DRC, Natural Sciences and Engineering Research Council of Canada Undergraduate Student Research awards to SD and JB, Weed Science Society of America undergraduate research awards to AA, SD, LM, and JB, and by Trinity Western University.\u003c/p\u003e\u003cp\u003eCompeting Interests\u003c/p\u003e\u003cp\u003eThe authors have no relevant financial or non-financial interests to disclose.\u003c/p\u003e\u003ch2\u003eAuthor Contributions\u003c/h2\u003e\u003cp\u003eDRC developed the study\u0026rsquo;s conception and all authors contributed to the study design. Data collection was performed by SD, AA, JB, and LM. Analysis and mapping were performed by SD, AA, and JB. The first draft of the manuscript was written by SD, and all authors commented on subsequent versions of the manuscript. All authors read and approved the final manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgements\u003c/h2\u003e\u003cp\u003eWe thank Hannah Munnalall, Alexis Graves, Jadon Deffenbaugh, Megumi Metcalfe, Jihyun Lee, Melissa Graves, Benett ImBeau, and Maia Olson for their assistance in the field surveying. Special thanks to Kathy Ma Green from Fraser Valley Invasive Species Society for her field data collection advice. We acknowledge Brian Colleran for helpful comments on a previous version of the manuscript. We are grateful for funding support from the Natural Sciences and Engineering Research Council of Canada, the Weed Science Society of America, and Trinity Western University.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAguilera AG, Alpert P, Dukes JS, Harrington R (2009) Impacts of the invasive plant \u003cem\u003eFallopia japonica\u003c/em\u003e (Houtt.) on plant communities and ecosystem processes. 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Retrieved May 17, 2022, from \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://globalnews.ca/news/8380618/british-columbia-state-of-emergency-floods/\u003c/span\u003e\u003cspan address=\"https://globalnews.ca/news/8380618/british-columbia-state-of-emergency-floods/\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"biological-invasions","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"binv","sideBox":"Learn more about [Biological Invasions](https://www.springer.com/journal/10530)","snPcode":"10530","submissionUrl":"https://submission.nature.com/new-submission/10530/3","title":"Biological Invasions","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"knotweed, rivers, flooding, climate change, rhizome spread, invasive species","lastPublishedDoi":"10.21203/rs.3.rs-7456717/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7456717/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe knotweed species complex (\u003cem\u003eReynoutria\u003c/em\u003e spp.) constitutes one of the most invasive plant taxa globally. Knotweed dispersal mechanisms facilitate rapid spread along waterways. The 100-year Pacific Northwest flood of November 2021 impacted British Columbia\u0026rsquo;s Vedder-Chilliwack River and its biota both through historically high rates of discharge and altered fluvial morphology including formation of new islands in the river and removal of existing vegetation. According to our field surveys, a five-fold increase of knotweed patches was observed in 2022 along the Vedder-Chilliwack River as compared to 2019. Much of the knotweed population increase occurred in newly available disturbed areas created by the flooding. Knotweed patches in the river\u0026rsquo;s tributaries tended to be well-established whereas the age distribution in the mainstem was skewed towards younger age intervals, indicating tributaries may act as a major source of population growth if not controlled. Knotweed in densely concentrated areas along the river was resurveyed in subsequent summers. Knotweed continued to expand, with 21% more patches in 2024 than in 2022 followed by a 97% increase in 2025 relative to 2024. The near doubling of the knotweed population in 2024 was likely connected to a significant rainfall event in October 2024. Both the 2021 and 2024 flooding events are consistent with the global increase in flooding frequency and intensity due to climate change. Such flooding events can significantly contribute to the expansion of invasive plant populations in waterways, highlighting the crucial need for targeted management in river systems to mitigate further spread across watersheds.\u003c/p\u003e","manuscriptTitle":"Implications of extreme flooding events modifying fluvial geomorphology for dispersal of knotweed (Reynoutria spp.) in the wake of climate change","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-09-04 19:07:17","doi":"10.21203/rs.3.rs-7456717/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"","date":"2025-08-28T08:58:21+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-08-27T15:28:24+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"Biological Invasions","date":"2025-08-26T21:09:55+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-08-26T10:00:03+00:00","index":"","fulltext":""},{"type":"submitted","content":"Biological Invasions","date":"2025-08-25T16:00:30+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"biological-invasions","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"binv","sideBox":"Learn more about [Biological Invasions](https://www.springer.com/journal/10530)","snPcode":"10530","submissionUrl":"https://submission.nature.com/new-submission/10530/3","title":"Biological Invasions","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"bcbeb81d-0747-44f0-99b7-085a7158d3da","owner":[],"postedDate":"September 4th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2026-01-05T16:03:41+00:00","versionOfRecord":{"articleIdentity":"rs-7456717","link":"https://doi.org/10.1007/s10530-025-03740-z","journal":{"identity":"biological-invasions","isVorOnly":false,"title":"Biological Invasions"},"publishedOn":"2026-01-04 15:58:04","publishedOnDateReadable":"January 4th, 2026"},"versionCreatedAt":"2025-09-04 19:07:17","video":"","vorDoi":"10.1007/s10530-025-03740-z","vorDoiUrl":"https://doi.org/10.1007/s10530-025-03740-z","workflowStages":[]},"version":"v1","identity":"rs-7456717","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7456717","identity":"rs-7456717","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}