Maine is under attack from species that don’t belong here. And they are getting a great deal of help from the effects of climate change.
The Maine Department of Agriculture, Conservation and Forestry’s Division of Animal and Plant Health has added 27 plant species to it “do not sell” list. As of the end of this year these plants may no longer be bought or sold in the state due to the threats they pose to native species.
Several of those terrestrial plants added to the list landed there thanks to warming temperatures making Maine a more hospitable place for them to put down their roots. Luckily, Maine’s winters are so far still cold enough to keep potentially destructive invasive mammals from moving in.
Warming temperatures due to climate change have made conditions favorable for some invasive plants to thrive and outcompete native species, according to Gary Fish, state horticulturist with the Maine Department of Agriculture, Conservation and Forestry.
“Climate change will exacerbate the invasiveness of almost all the plants listed in 2018 and the ones scheduled to be banned in 2024,” Fish said.
“One of the main ones we looked at is the Bradford or callery pear tree,” Fish said. “In other states where it has established itself there are actually bounties on it.”
Fish does not think Maine will set up a bounty on the popular southern ornamental that has lovely flowers but a smell often compared to rotting fish. He did say if it does get a foothold in the natural landscape it would have a devastating effect on native species such as paper birch, aspen and cherries by taking over and crowding them out.
Also new to the list are two kinds of bamboo that, at the moment, are not able to withstand Maine’s coldest months. Fish said as the state continues to experience warmer winters, they could establish themselves and easily crowd out native species.
The two bamboos — golden bamboo and yellow groove bamboo — are among the fastest growing bamboo species. They spread via underground plant stems that can easily escape confinement. Once free, the bamboo forms a dense monoculture and thick layer of leaf litter that destroys native plants and takes over an ecosystem. These plants like warm weather and full sun.
“The warming climate is going to be the fuel that some of these plants need to let them produce and thrive like they do in other parts of the country,” Fish said.
For other species, climate change had nothing to do with their inclusion on the list. Instead, they are viewed as plants that pose threats to the state’s economy or environment because they have the ability to establish self-sustaining populations outside of managed cultivation.
Home landscapers love European mountain ash. Leafy branches and red berries make it an attractive ornamental. But it can also be easily spread by birds who eat those berries and poop out the seeds. Once it starts growing in the wild, European mountain ash can become the dominant species and crowd out even native ash trees.
Others you can no longer purchase in Maine after the end of the year include creeping Charlie, which is often recommended as an alternative to lawn grass; sea buckthorn; dwarf honeysuckle; Christmas berry; and coltsfoot.
When these invasives do escape, it’s bad news for native species, according to Fish.
“Invasive plants are a direct threat to Maine’s natural and working landscapes,” he said. “The aggressive growth of invasive plants increases costs for agriculture, can affect forest regeneration, threatens recreational experiences, and reduces the value of habitats for mammals, birds and pollinators.”
A good example of one of those species is barberry, an ornamental shrub that, if it establishes, will completely crowd out everything from shrubs to valuable timber.
“If you cut trees in an area, the barberry can come in and soon all you will have is barberry,” Fish said. “It will completely dominate the site and that’s a perfect example of economic and ecological harm.”
Barberry also forms dense, prickly thickets creating the kind of habitat favored by Lyme disease-carrying deer ticks.
Maine’s winters still remain cold enough to prevent the spread of invasive animals. Strict laws governing what kinds of species can be brought into the state also help control them, according to Nathan Webb, director of the wildlife division with the Maine Department of Inland Fisheries and Wildlife.
“We have pretty strict regulations on importation of what we consider exotic or non-native species,” Webb said. “And Maine is unique because, unlike a place like Florida, our severe winters limit a lot of what species can survive here.”
For example, Webb said there is no way the Burmese python — a snake that is exploding in population in Florida — could ever survive here.
As strict as the rules around exotic pets are, Webb said there have been some to successfully live in the Maine ecosystem.
“One that we do have here is a turtle called the red eared slider,” Webb said. “It was available for private ownership, and some were released by their owners into the wild.”
Webb said there are not a huge number of the turtles wandering around Maine, but he said his agency is keeping an eye on their numbers and any potential impacts to native species.
“These plants and animals don’t fit into our ecological bubble, and they don’t provide the food or shelter our native species need to sustain their populations,” Fish said.
“They impact the ecology by disrupting the food web or cause economic harm to farmers or forests.”
