Managing invasive species on a stream bank

I recently started volunteering at a local conservancy. I’ve been asked to remove invasive species, in areas where there will be planting of native species later this week.

I was thinking of this thread while working this morning. A lot of what I’m removing lately is Reynoutria japonica that grows thickly on the banks of a shallow stream. It is evidently one of the species responsible for preventing degradation of the bank, along with the native trees and a very small handful of smaller native plants.
I’ve chosen to leave the roots of the larger plants in the ground for now, while being sure to cut off all the leaves. Not that R. japonica has a particularly extensive root system to begin with.
Here’s photos of a spot I did this morning.
I know it can regrow later, but I’ll be continuing to monitor and manage the area while the new natives settle in.

Was that the right thing to do? Or is there a better option? How much of a difference does it make that the removed plants are going to be replaced soon after?

In the area there’s also some multiflora rose, which I’m going to get next; and Ampelopsis glandulosa, etc.

Any tips for a beginner appreciated.

6 Likes

What a terrific volunteer effort. :) I would look forward to hearing ongoing reports of your project. Meanwhile, is there a knowledgeable conservancy person who could answer your question about the roots?

3 Likes

In the thread you linked to I mentioned that knotweed control was part of our river restoration project for the same reason (native plant restoration) you folks are controlling it. It crowded out our efforts to restore native species and there were large concentrations of it on the streambank. Thinking around these sorts of projects has undoubtedly moved on since then but our experience seems relevant to what you’re doing. We consulted folks at the local arboretum who told us that the options were herbicide, yanking it out or stomping it. Herbicide would cost money, yanking/digging it would be a lot of work and disturb soil in a vulnerable site and stomping it was dead simple, left the soil undisturbed and could be done by volunteers.

There was an annual river cleanup every spring that involved a 100-200 volunteers. Most folks picked up garbage from the banks and pulled shopping carts and whatnot out of the rivers (my favourite find was a sailboat on a trailer that turned out to have been stolen months previously). Other crews had other tasks and knotweed stomping was popular. A professional horticulturist led the crew who went to the sites and reduced the knotweed to rubble.

Knocking the plant down allows slower growing stuff to get established. It does not eliminate the knotweed, at least immediately. We went back as smaller groups led by project staff and individual members of the crew trained by the horticulturists to knock back the plants that made an effort at recovering through the summer. We did it every year for years; over time the native plants (trees and shrubs, at least) became established and the knotweed retreated. It involved a longterm commitment to both knocking back knotweed and nurturing the plantings but we eventually got where we wanted to go.

An important side-benefit was the longterm involvement of many community members in control of an invasive species. I had folks approach me at events for years after wanting to chat about how much they had learned and how much fun it had been.

10 Likes

I am a mere observer of Reynoutria japonica in my area, and from what I’ve seen, it will grow back, you can be sure of that. It is an extremely tenacious plant.

Assuming control is even possible, I suspect it is a multi-seasonal effort. I look forward to hearing more about that.

4 Likes

I’m looking after a pretty small area (about 100 meters by 20 meters of trail/stream/mixed wetland) and I’ll be visiting once or twice a week for the next year, potentially for multiple years depending where I resume college next Fall. As one of the few volunteers with a biology background I’ve been asked to monitor water quality, and do periodic inventories, as well as weeding.
I’d be happy to post updates. Maybe as a Journal, not sure the Forum is the best place for that.

6 Likes

Reynoutrias are plague and they’re one of those invasive plants that fill all the place, not letting other plants grow and they’re large. So yes, getting rid of them is a good thing, especially if you can monitor the site and see results.

1 Like

I don’t know anything about Reynoutria japonica. My mom volunteers for a nature preserve and they use a method for removing invasives where you cut down the bush or tree to a short stump and immediately paint the stump with undiluted Round-Up herbicide (glyphosate). Usually the plant dies. If it does survive, it barely grows, looks kind of like a bonsai. Don’t use this method if there is rain forecasted in the next 24-48 hours. It will wash off the herbicide.

1 Like

Have you reached out to any local officials for advice? They may know about the particular concerns of your area.

haha well obviously I’m going to ask the volunteer manager / park manager and not just you guys…

4 Likes

The smallest fragments of the root or stem of Japanese knotweed will all of them grow back like crazy. It is extremely difficult, if not impossible, to eliminate the plant, and I am not sure that any native species can successfully compete with it. I have seen people cover an area completely with black tarps in order to discourage the knotweed. That does work reasonably well.

5 Likes

It’s great that you’re helping to cull invasive species!! I wonder, could you possibly replace the roots of R. japonica with some other native plants species as you go digging them up? Or use some sticks and rocks to cover the bank and prevent degradation? That way you can take care of the plants once and for all and don’t have to keep removing them as they grow back. Also, is there any local animal that may feed on them? Perhaps you could encourage population growth for those species as a way to naturally manage the plants.

1 Like

The local cooperative extension (https://njaes.rutgers.edu/county/) may be a good starting point for that

4 Likes

That sounds like a small enough piece of real estate that you could manage to beat it back over time.

If you are not going to remove the roots then you might want to try the stomping approach. You don’t gain much from cutting it. We didn’t bother removing the knocked-down material. The approach we took was to let the plant finish its initial spring growth spurt then knock it down before it starts regaining energy reserves from photosynthesis. It never got the chance to set seed and the continued knocking down of new growth meant that it didn’t get to replenish energy stores for winter.

The objective was not so much eradication as it was to give the native plants a fighting chance until their root systems were established and the larger woody plantings were tall enough that they didn’t need to worry about the knotweed. We used larger bare root stock of quick-growing species of trees (silver maple, ashes, etc). As I recall we were able to establish red osier dogwood and I think one or two Viburnum species, as well. Salix self seeded in a couple of spots and we helped it along by knocking back the knotweed.

It’s important to keep knocking it down. If you’re there weekly, make the stomping of knotweed a weekly thing. We did whatever we could to help the plantings in addition to crushing knotweed. We used wood chip mulch abundantly. We watered selectively. We pruned to promote vertical growth and help healing from damage from drunk morons.

It sounds like your project is structured such that a comparative study of approaches might be possible.

If you end up leaving the area, make sure at least a couple of folks know how to continue what you’re doing.

4 Likes

I came to this thread because I run a wetland Conservancy near Johannesburg in South Africa.
Each invasive plant has to be dealt with differently so I suggest you research each one for the optimum removal methods, especially where herbicide is required.

Invasive plants respond to different chemicals and application methods, but the majority of herbicide chemicals are poisonous in a wetland.
Glyphosate is a general broad-leaf herbicide but most brands contain surfactants which are poisonous to frogs. There will be water-safe brands which you can use so check the MSDS of each one.

3 Likes

You could greatly benefit from examining results from other conservation properties that have programs for invasive removal. A slap on the wrist doesn’t work for the serious ones, particularly not Reynoutria japonica. It took us four years to remove it from a small meadow in a nearby U.S. national park, and the final effort did involve careful herbicide. Each year was an improvement, and removing much of the density helps, but cutting it can be very stimulating. It’s a war, not a battle or skirmish.
I was trained in invasive plant management, and there are public resources to see how it should be done. Site remediation won’t happen in a day. As you’re putting in the native replacements for erosion control, preparation includes removing the invasive roots, and taking care not to distribute more invasive material.
Here’s just one guide, from the U.S. https://www.agriculture.nh.gov/publications-forms/documents/japanese-knotweed-bmps.pdf
It’s an ongoing headache, but the alternative is terrible. Time put into making a successful management plan will pay off. So, wishing you good luck, patience, the discovery of a predator, and intestinal fortitude. Strongest thanks.

6 Likes

Went back today. I’ve created a Journal post, anyone interested in updates can follow there.

3 Likes