Japanese Knotweed
Knotweed .. its neither a knot nor a weed.. discuss. (Can anyone name that 90’s throwback??)
Let’s dig in. Japanese knotweed as its first name suggests comes from Japan and other parts of temperate Asia. It was originally introduced to this land in the late 1800’s as an ornamental. Prized for its bamboo- like stems, quick abundant growth, and flush of dainty white flowers that sway in the Summer wind this plant was kept in nursery stock up until the early 1900’s. Japanese knotweed took quite well to its new home and being an adventurous free-spirit, soon escaped cultivation and naturalized in many areas around the United States. Seeming to overtake and overcrowd native species that had been thriving in the riparian ecosystems that Japanese knotweed now called home, the plant was soon listed on the invasive species list of many states and subsequently stopped being sold.
No longer being spread by humans in the plant trade, Japanese knotweed used its own resources to spread its genes and presence in this land. Abundant flowers whose nectar is loved by bees are pollinated leading to formation of seeds that are spread by birds, and water. Rhizomatous roots enable the plant to form large colonies, a masterful way of vegetative propagation that circumvents the need for pollinators.
Where I live in Winooski, VT Japanese knotweed is a common sight along the Winooski river. The towering growth outcompetes the plants that once made up the foundation of this riparian ecosystem.
Bees do love the nectar of the flowers but the shore is quickly turning into a monoculture, lacking the once rich diversity of plant life that sustained many animal species. How did Japanese knotweed get here? And what enabled it to become so prolific?
The Winooski river currently has 17 working dams built throughout its meanders. More were once active and have since been abandoned. The first dam was built over 220 years ago to power the factory mills that fueled the mill economy of the town of Winooski. The dams active now are mostly used as hydro-electric power sources with a few still guarding against floods near larger towns. When a river is dammed the course of the river becomes more controlled, no more seasonal flooding over the floodplain area due to increased water flow. The water flow is very much regulated by the mechanics of the dam. Plants that inhabited the floodplain before the dams were built thrived in an ecosystem that allowed intermittent flooding. Willows, buttonbush, alders, eastern cottonwood, sweet viburnum and river grape are some of the many species that thrive in the particulars of the riparian ecosystem. With the cessation of the floods and some of the best soils created by the alluvial floodplain cleared of its native vegetation for agricultural use, these plants began to recede long before the arrival of Japanese knotweed.
One can argue that Japanese knotweed is filling a niche. Its tenacious roots provide erosion control which keeps sediment from the stream bank from dropping into the water. Nectar from its flowers provide a food source for insects who in turn are a food source for birds and fish who are then consumed by larger mammals higher up the food chain. Japanese knotweed benefits humans too. Young shoots of the plant - which resemble asparagus - are edible when boiled. Naturopaths have been using Japanese knotweed, which contains a compound called resveratrol, to combat Lyme disease with great results. This is an especially generous offering considering that tick populations and the Lyme disease they can carry have been on the rise in New England.
The management strategy promoted by the VT Fish and Wildlife Department calls for removal of this invasive plant through the use of mechanical and chemical strategies. It is suggested to continually cut down the new growth throughout the growing season for a few years to weaken the plant so that when inter-planted with native plant species the new plantings have time and space to outgrow the Japanese knotweed. This treatment can be supplemented with timed applications of chemical herbicide, namely glyphosate, which is safe (?) to use near water. These strategies are effective at removing Japanese knotweed and yet a larger question looms - will the newly planted native species be able to survive in an environment which no longer resembles the riparian ecosystem that they once knew? How can we honor what this immigrant species has to offer at the time as making space for native plants to thrive?