There are a lot of reasons to want to control the non-native plants that have invaded the state of Maine.
But recent scientific research done on Japanese barberry adds one more big one to the list: the dense, thorny shrub actually creates a microclimate that is good for ticks. And that is bad news for people.
“Barberry thickets actually make a pretty good habitat, not just for ticks but for some of their host species,” Susan Elias, a research associate at the Lyme and Vector-Borne Disease Laboratory at the Maine Medical Center Research Institute in Scarborough, said this week. “You’re creating a perfect storm, when you have these non-native species coming into the landscape.”
Japanese barberry was introduced to North America in the 19th century by landowners who wanted to use it for hedgerows and other plantings, according to the New England Wildflower Society. But barberry didn’t stay where it was planted. Its bright red berries are attractive to birds, especially wild turkey and grouse, and those hungry birds helped to spread the shrub around the landscape. Perhaps because of the very sharp thorns, deer don’t browse on the plant and check its growth that way. Long after a homestead has been abandoned, Japanese barberry persists, according to the wildflower society’s website.
It is established as far north as Nova Scotia, as far south as South Carolina and as far west as Montana, according to the University of Maine Cooperative Extension. Today, the invasive species is found in all six New England states and has been prohibited in Maine, Massachusetts and New Hampshire. And it can change the forest, Elias said.
“There are places in southern Maine where barberry has completely taken over the understory of the forest,” she said. “You’d be amazed at how thick and tall the barberry can get. The barberry suppresses the regrowth of species. You aren’t going to get blueberry. You aren’t going to get huckleberry or even the native tree species. Barberry forms a dark thicket, and very little can survive those shady conditions.”
Very little other than ticks, and the mice and other species that host the ticks, that is. She and other researchers from the Lyme and Vector-Borne Disease Laboratory started to look into barberry about a decade ago, after they got a grant from the United States Centers for Disease Control to study the habitats associated with deer ticks. At that time, it was basically known that deer ticks were associated with hardwood or mixed forests, not coniferous forests.