Woodland invasion

Japanese knotweed (Reynoutria japonica) is popping up more in Waupaca County.

The non-native bamboo-like plant is hard to eradicate and grows back thicker when cut. It is one of many invasive species that have taken root in the area.

“They’re localized populations. I have some of it in town [Waupaca] by me. There’s some by the treatment plant. There’s a population by the Chain O’ Lakes. There is some on city land along Smith Road. It’s tough. It’s got a vast root system so it can be difficult to control especially without a chemical treatment,” said Jordan Westrick, a DNR forester stationed at Hartman Creek State Park.

It invades everywhere: upland and lowland sites, disturbed and undisturbed lands. There was a theory that its seeds were not viable for reproduction. That has been dismissed and some populations have been found to be created from seed. Usually it spreads through the rhizomes. It can grow up to 8-feet tall.

Westrick recommends chemical application to destroy it.

“It keeps coming back every year if you just cut it,” he said.

Oriental bittersweet
“From what I’ve seen in Waupaca County, it’s starting to get a grasp in certain areas where it is becoming a huge problem. From my experience and what I have seen, I would consider oriental bittersweet as one of the worst invasive that you might come across on your property and should be dealt with as soon as possible,” said Westrick.

Oriental bittersweet (Celastrus orbiculatus) is a vine that wraps itself snake-like around the trunk of a tree and climbs all the way to the top canopy. It also forms dense mats on the forest floor.

Of the invasive plant species in the county, it is the only one that can kill mature trees by girdling the them (constricting the vascular tissue of the bark). Westrick said sometimes it can look like a braided rope it grows in a way that it looks like it is strangling the tree.

“Where I’ve seen it the most is down in Caledonia and Waupaca as well, pretty thick in area. I’ve worked with landowners in the New London area that have had their entire forest carpeted with bittersweet. It sprouts from the root rhizomes. It won’t look like a vine in the first couple years but it will eventually keep climbing its way up,” said Westrick who had it in his own yard.

He treated the foliage with glyphosate during the growing season with success.

Buckthorn
Common buckthorn (Rhamnus cathartica) is a small hardwood tree from Europe. It takes advantage of the mid-story of the forest, blocking out sunlight in dense thickets that makes it hard for native species to sprout and grow. It spreads by thousands of berries which can be dormant in the spoil and be viable up to seven years.

Westrick points out that research show that around 90% of those seeds will germinate in one to two years. Seeds are also distributed by birds eating, digesting and releasing them wherever they fly.

It holds its leaves late into the season, cluttering up the view for hunters but also makes it easier for identification. When leafless, it slightly resembles native black cherry.

“It’s a lifelong battle. Once they are there, it’s almost impossible to eradicate them completely. If you do nothing right now and have a small population, it’s just going to continue to get worse. The worse it gets, the more discouraging it is. If you can start somewhere and get the population to a point that is manageable, and in follow up years, you will have follow up plants and it will be only some maintenance,” said Westrick.

Autumn olive
Autumn olive (Elaeagnus umbellate) is thorny species that is half-tree, half-shrub that like buckthorn, chokes out native species by dominating the mid-canopy of the forest. It can form massive thickets that make any kind of hiking miserable. The tell-tale identifier is the shiny silver underside of its narrow oblong leaves.

Honeysuckle 

Amur honeysuckle (Lonicera maacki) can be identified as roundish shrub with a shaggy, peeling bark that resembles nothing else like it in the woods. It is one of the earliest plants to leaf out in the forest in the spring. Like autumn olive and buckthorn, it blots out sunlight to lower-growing native plants. When cut the wood has a sweet smell.

“It’s one of the original invasive that have been around for so long. I don’t see it as aggressive as some of these other invasive out there,” said Westrick, noting that the only good thing about it is that it doesn’t have thorns.

Japanese barberry
Japanese barberry (Berberis thunbergii) is a shrub that has small, thin thorns that are sharp as hypodermic needles. It produces bright red berries in the fall that often hang on throughout the winter. It can range from knee-high to chest-high in height and an infested forest will have clumps of it growing everywhere.

“Barberry is on the top of my list for what I see in the county and being a problem. I see it more in the central and southern parts of the county, not as much in the north. If you can catch those early you can stop the spread. I’ve seen forests that are a carpet of barberry. You won’t dare walk through there,’ said Westrick.

He noted that studies have shown that barberry is a breeding ground for ticks as they make good cover for rodents.

Stop the spread
Nearly all methods to eradicate these species involve cutting and chemical application. Westrick points out that the DNR has data sheets for each species with information on the best chemical to use for the job and how to safely use them. He is happy to work with local landowners and answer questions about this topic. Getting started online, the most comprehensive local resource is the DNR’s specialized webpage at dnr.wisconsin.gov/topic/Invasives.