A Hard Rain’s Gonna Fall
Colleran, B. P., & Goodall, K. E. (2014). In Situ Growth and Rapid Response Management of Flood-Dispersed Japanese Knotweed (Fallopia japonica). Invasive Plant Science and Management, 7(1), 84-92. http://dx.doi.org/10.1614/IPSM-D-13-00027.1
Written by Brian Colleran, edited by Sofia Al-Shayeb
Summary
With the increase in extreme weather events brought on by our changed climate, invasive plants that stand to benefit from such disruptive events will be even more disruptive to the ecosystems and species impacted by their presence. In the wake of Tropical Storm Irene on August 28th, 2011 Vermont officials were worried about the likely spread of knotweed. Past localized flooding had been associated with the spread of the plant, and statewide flooding was expected to result in a statewide increase in the population. Following Early Detection and Rapid Response management of flood distributed propagules by Vermont Youth Conservation Corps crews, black plastic trash bags were randomly selected from several management sites along different Vermont rivers, and the knotweed within examined. Among other things, it was found that 70% of new plants were growing from rhizome (an underground part of the plant, which is a modified stem, rather than a root) fragments, meaning the bank containing them had to have eroded during the flood. Therefore the population of knotweeds along rivers appears driven by erosion rather than sexual reproduction, (supported by genetic analysis, Gaskin et al. 2014). This drives a positive feedback loop between flood damages, streambank failure, and the spread of knotweed along waterways. Beyond ecology, this has significant implications for both climate and non-climate resiliency of infrastructure and private property, water quality, expected uses of emergency funds at all levels of government, and expectations for first responders responding to severe flooding. While this work cannot aid in the control of new knotweed stands, it does show that early interventions can successfully prevent the infestation of new areas by these plants.
Take Home Points
Knotweed spread by flooding is an ideal candidate for early detection and rapid response management. New plants and the flood distributed propagules they grew from, were wholly extracted by hand throughout 2012, until June 2013 when rhizomes grew too extensive for full removal by hand (Colleran & Goodall 2015).
Due to knotweed’s undermining of streambanks, which amplifies and exacerbates flood damages, knotweed control contributes to lower post-disaster emergency expenditures, higher water quality, and better riparian ecosystem recovery from the flood.
positive feedback loop: flood damages & streambank failure & spread of knotweed along waterways
Management Implications
In the months following a flood, control work is cheap, meaningful, and highly effective.
The stands of knotweed most likely to spread downstream during floods, those along streambanks, are ideal opportunities for climate resiliency work.
Knotweed along the streams can jump to the roads and vice versa at road-stream crossings. These are ideal locations to prioritize control to interrupt the spread on both networks
The plant itself is the “seedbank”
Controlling stands along waterways is one of the most effective ways to interrupt the spread of these plants, preventing their establishment downstream in the wake of floods.
Related papers
This research summary is part of a series on the link between hurricanes and invasive species. For other research summaries on this topic see: Falk et al. 2024, Kraemer et al. 2017 and Bhattarai and Cronin, 2014. For the Research-to-Practice paper (R2P2) on this topic see: Rock you like a hurricane: The perfect storm for an invasion and Colleran and Goodall, 2015, which is a continuation of the work summarized here.
Keywords
Flooding, erosion, early detection, rapid response, knotweed control, climate resiliency, climate change, fluvial geomorphics