Invasive species threatening New England’s plant life

Garden in the Woods is one of Boston’s local treasures. It aims to recreate the diversity of the region’s different habitats, from bogs to ponds, floodplains to sand plains. 

Garden in the Woods is “one of the most beautiful, and one of the oldest, naturalistic gardens in eastern North America,” says Elizabeth Farnsworth, the senior research ecologist for the New England Wild Flower Society at its 30-acre woodland garden. “It has a wonderful selection of native plants that you can use in your own garden, but that are also broadly representative of the habitats of New England,” Farnsworth says.

The garden is also the showcase and laboratory for the New England Wild Flower Society, which recently released its “State of the Plants Report,” the most comprehensive assessment of native plants and plant communities ever assembled in the region.

About 3,500 species and subspecies of native plants grow in New England. They are used to tough winters, but now they are under stress from climate change, development and invasive species.

“About 22 percent of our native flora are regarded as rare — that is endangered, threatened, special concern, or even historic in one or more New England states,” Farnsworth says. “Close to 100 species are now no longer known [in] New England. They may exist elsewhere, somewhat precariously, but they're no longer here. That’s a pretty substantial number.”

The majority of the region’s flora is native. About 30 percent have been brought from elsewhere or introduced purposefully or mistakenly, which Farnsworth says is about on par with other regions of the country. About 111 species, or 10 percent of that set of non-native species, are regarded as invasive.

“Invasive means that these are plants that can grow quite aggressively,” Farnsworth explains. “They can overtake native plants; they can outcompete them. They can come to dominate a particular habitat so [much that] it becomes very impoverished in terms of plant diversity and often animal diversity.”

“It's really important that we understand that plants are the foundation,” Farnsworth adds. “When you start losing important species, and the diversity of species, then pretty soon, as Rachel Carson alluded to many years ago, you won't hear the birds, you won't encounter the animals, you won't see the butterflies — and then you make get an inkling of just how impoverished the natural community around you has become.”

Trees in the region also face a number of stresses. Hemlock trees have been attacked by a tiny white insect called the hemlock woolly adelgid, which is spreading across New England and has been spotted even further north. Ash trees are being killed or weakened by the emerald ash borer, which is moving into western portions of New England. Sugar maples, an iconic New England tree that is also important to the region’s economy, are showing some signs of being stressed by warmer temperatures.

In general, researchers are “already picking up a signal that certain plants are responding very strongly to climate change,” Farnsworth says. “Some plants are flowering, on average, two weeks earlier in the spring than in past years. The flowering behavior is, of course, important to pollinators. If there is an offset between early flowering plants and the emergence of their pollinators, both parties are going to be unhappy.”

Farnsworth wants the report to begin a national conversation. “Each of the different states are sort of doing their own thing,” she says. “Some states are working harder than others to maintain their native flora. Some states have more resources than others. Perhaps we can collaborate.”

This article is based on an interview that aired on PRI's Living on Earth with Steve Curwood.