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Warmer winters feed into growth and spread of invasive plants in Connecticut

A nearly solid mat of the invasive and non-native Japanese barberry bush in a New England forest.
Robert Winkler/Getty Images
A nearly solid mat of the invasive and non-native Japanese barberry bush grows in a New England forest.

The warm winter is making it easier for invasive plants to grow, spread and thrive in Connecticut and across New England.

According to the Connecticut Invasive Plants Council, the state has more than 90 identified invasive plant species, which can arrive from more southern states through bird migrations and the wind.

Bonnie Burr with UConn’s College of Agriculture, Health and Natural Resources, said those invasive plants are thriving more because of warmer temperatures, sunlight and moisture.

“When [the] growing season gets warmer, gets longer – that just gives our invasive plants a greater opportunity to expand,” Burr said. “We see them become much more dense in terms of how they infiltrate within our native plant populations.”

Burr said her department is still seeing too many invasives that have not died off this season. She said curbing invasive plant growth requires temperatures dropping below freezing for at least 10 days.

But freezes have been hard to come by this year. Last month was New England’s warmest January on record and the seventh-warmest January globally, according to climate reports from the National Oceanic and Atmospheric Administration.

Randy Prostak, a University of Massachusetts Extension weed specialist, said the warmer weather could lead to longer growing seasons for invasive plants and cause them to spread more quickly.

“The bigger the plant gets, the healthier it gets, the more likely it’s going to be able to flower and produce more seed, which is going to drive that forward,” Prostak said.

Invasive plants can overgrow and outcompete native plants, according to the Connecticut Invasive Plant Working Group (CIPWG). The group has identified species like common reed and garlic mustard among the top invasive plants of concern. Japanese honeysuckle and Japanese barberry are also among plants of concern, according to the CIPWG.

Invasive plants are benefiting tick populations

A 2019 report presented to the U.S. Department of the Interior said invasive plant species like Japanese barberry can give ticks an “unnaturally beneficial” habitat.

Dr. Megan Linske with the Connecticut Agricultural Experiment Station said she has seen how Japanese barberry is benefiting populations of deer ticks in the state.

“It tends to leaf out really early, capitalize on the sunshine and the warmth that comes with these warmer winters,” Linske said, adding that it creates dense thickets that many tick species want to be in for a long time while seeking a host.

Burr, with UConn, said invasive plants easily acclimating to the warming climate raises a red flag.

“It’s their ability to get in and really create havoc,” Burr said. “That really, really has us concerned about … how invasives are coming in and staying.”

To report an invasive plant species sighting, the Connecticut Invasive Plant Working Group is asking people to email info@cipwg.org with photographs and details of the finding. More information is outlined on the CIPWG website.

As Connecticut Public's state government reporter, Michayla focuses on how policy decisions directly impact the state’s communities and livelihoods. She has been with Connecticut Public since February 2022, and before that was a producer and host for audio news outlets around New York state. When not on deadline, Michayla is probably outside with her rescue dog, Elphie. Thoughts? Jokes? Tips? Email msavitt@ctpublic.org.