Knotweed is not our friend
On May 27, Timothy Scott wrote an opinion piece for The Times Argus that I believe is worth rebutting. I can understand how Mr. Scott, as a man who makes a living in herbal medicine, can appreciate Japanese knotweed as a useful plant, since he uses it to help treat Lyme disease, and he sees the hand of fate in the luck of having his preferred treatment spreading with the disease. I can also appreciate the other uses for it that he mentions, such as it being an edible plant, a potential biofuel, and that it can clean contaminants out of the soil. I can certainly support these uses for knotweed.
However, I cannot agree with Scott referring to the spread of knotweed in Irene-affected areas as “nature doing what nature does.” A central part of my role with the state of Vermont is to educate people about the threats that invasive species pose both to the natural environment and the spaces we create, including farms and neighborhoods. Knotweed is an invasive species, which means that it is a non-native plant that is not limited by local competitors, predators or diseases. Unlike other non-natives that have escaped from our farms or gardens, this lack of constraints allows knotweed to grow unchecked, eventually excluding all other plant species in the places it has become established, which is most commonly along our rivers and roadsides.
Mr. Scott also incorrectly asserted that knotweed plants “help stabilize the soil and create biomass to enrich the land.” In fact, one of the most harmful effects of knotweed is the destabilizing effect it has on riverbanks. Knotweed produces a chemical from its roots that makes it harder for other plants to grow. This effectively eliminates groundcover plants that prevent soil from washing away, and mature trees with deep roots that provide structure along the bank are slowly isolated as seedlings fail to grow within the knotweed patch. The knotweed itself benefits from erosion, as its primary means of spread is the distribution of pieces of plants along rivers and roads.
In addition, knotweed can also severely impact our built environment. It can grow through weak spots in concrete and asphalt, which has resulted in some devastating situations. In England, homes have needed to be demolished, mortgages are denied, and exorbitant removal costs must be tolerated, all due to knotweed.
Knotweed, like any other invasive species, eventually overwhelms an invaded ecosystem, transforming these spaces into ecological wastelands, devoid of their normal diversity of native plants, animals and insects. This is not a simple situation of “nature doing what nature does” — it is a foreign invader taking advantage of a system that is not prepared to deal with it, and then destroying that system.
The mistake Mr. Scott seems to be making is equating individual species with “nature” as a whole. The success or failure of a particular species or ecosystem in this day and age is nearly impossible to ascribe to “nature.” The hand of humanity is rarely hard to find when looking at changes in the natural world. Prior to recorded history, plants and animals were generally not spread by humanity, and natural barriers limited their range. Now, zebra mussels hitch rides in the ballast water of ships, and exotic pets are released into the wild. In our modern, globalized world, species can arrive on a new continent as quickly as a jet can fly, often with devastating consequences to the local ecology. This is a far cry from “nature doing what nature does.”
As for Mr. Scott’s connection between knotweed and Lyme disease — ironically, it is the spread of another invasive species, Japanese barberry, that is promoting the spread of deer ticks, and Lyme disease, in Vermont. While I wish Mr. Scott the best in his work, I feel it is imperative to make sure that he does not misrepresent the facts about the very real threat to Vermont’s ecosystems and landscapes that knotweed, or any other invasive plant, presents.
The writer is an invasive species biologist for the Vermont Agency of Natural Resources.
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