Brian Colleran, M.S., CERP, PWS, AFB

I began my work with Japanese knotweed in the wake of Tropical Storm Irene in Vermont. The damage from that storm was incredible. My role at the time was to find a way to slow the spread of Japanese knotweed (Reynoutria japonica). At that time, land managers and naturalists knew that previous local floods had led to larger R. japonica populations, but didn’t quite know how or why.

In the course of my travels throughout Vermont to assess the needs I would address, I saw blown out riverbanks, flood debris in areas no one expected to flood, and the price that residents paid when waterways did the unexpected. I also saw knotweed growing out of the blowouts, growing out of the flood debris, and concentrated along waterways. I began developing a sense for where to find knotweed in flood plains, flood debris, and along waterways.

I also began hosting workshops, organizing volunteers, and trying my best to do my job. It was an impossible task. But when the Vermont Youth Conservation Corps (VYCC) announced they had crews ready to work on Irene recovery projects, I had a wealth shovel ready projects. The VYCC provided three weeks of crew work. After each work day, I grabbed a garbage bag of the plants removed that day, and brought them home. Prior to starting the crew work, a search of the available scientific literature and management fact sheets hadn’t offered any advice on how to help the crews succeed. If I wanted to get better at what I was leading, I needed to learn fast. I spent evenings and weekend collecting data - and insights - from those garbage bags.

Quickly, it became apparent most new plants were regenerating vegetatively. This means they were growing from a piece of a plant, rather than a seed. 70% of these new plants were growing from a piece of rhizome. So these new plants were growing from pieces of a plant that had washed downstream, and more specifically, from a formerly underground part of that plant.

One of the unusual features of Japanese knotweed as an invasive species is that it is clonal. Every invasive Japanese knotweed is a female, and arguably, all the same plant. But one of the hallmarks of an invasive species is out of control reproduction. Invasive knotweeds as a group have some workarounds. Giant knotweeds are all male, and if Japanese knotweed is nearby, their progeny is Bohemian knotweed. Bohemian knotweeds can go on to successfully reproduce sexually, as well as continue reproducing with its parent species (The genetics of a knotweed invasion can get pretty messy). But without any of these related species, the all female Japanese knotweed can be invasive all by itself. Erosion was the key to this puzzle! I published my work in the hope that the lessons I learned the hard way wouldn’t necessarily have to be re learned by a fellow land manager.

I presumed others already knew that erosion during flooding was a significant contributor to a Japanese knotweed invasion. Others must already be researching this relationship between knotweed and flood damage. After all, I had been hired based on such observations. I presumed the big study was going to come out soon.

It took a few years to realize this presumption was wrong, and no one was looking at the relationship between flooding, erosion, and knotweed.

Once I realized my knowledge was unique, I needed to find a place for it. R. japonica, and presumably its near relatives, amplify and exacerbate flood damages. Which means it’s linked to climate change resiliency. Bigger storms create more rain, and more rain is how floods start. If we have more floods, we’ll have more knotweed, and more of the erosion that spreads it. Knotweed, since it is invasive, impoverishes ecosystems and ends up forming green wastelands of uninterrupted knotweed. So the root systems of all the plants no longer on the riverbank have been lost. Both of these statements mean that controlling knotweed can protect infrastructure (And is probably cheaper than an insurance policy for a bridge. I can’t imagine that’s cheap). The roots of a tree hold the soil in place, which in turn holds the nearby bridge abutment in place. The removal of this invasive, and replacement with native species, would be a very normal ecological restoration project. Ecological restoration is not normally considered a conservative fiscal policy. Controlling this plant improves everything. So rather than the ecologists, I’ve tried to bring this knowledge to the highway department, and those working on climate resiliency.

I have more knotweed stories, and other non-knotweed ecological restoration insights. Most are from the Great Basin desert, California’s Central Valley, the Great Lakes region, or New England. I look forward to sharing them with you.