Invasive species keep coming. Will climate change bring more?
HAMDEN – Claire Rutledge is trudging through the swampy, weedy, poison ivy-covered and probably tick-infested banks of the Mill River in Sleeping Giant State Park. Those conditions are the least of her concerns.
Her concern is the white ash trees lining the floodplain. She stops by one.
“Beautiful tree,” says Rutledge, an agricultural scientist at the Connecticut Agricultural Experiment Station. Then she points up. “If you look up top there, see how few leaves it has left? Not much.”
The bare treetop – repeated on just about every ash tree Rutledge comes across – is a telltale sign of infestation by the Emerald Ash Borer, an invasive beetle that jumped the Hudson River into Connecticut three summers ago, a decade after it first arrived in the Detroit area from Asia. It’s now in 70 Connecticut cities and towns and all but one county — Windham, but the metallic green-colored critters are right on its border.
This summer the beetle represents only one of many invasive species the state’s natural science community is wrestling with. It’s an unexpectedly busy summer. with a new beetle attacking pine trees, a serious re-emergence of gypsy moths, a migrating mosquito that can carry dangerous diseases, enormous numbers of ticks and the unrelenting march of dozens of invasive plants.
“So we’ve got a few problems to deal with,” laughs Theodore Andreadis, the Experiment Station’s director. “Of course once they come in, without their natural complement of enemies, they usually cause havoc. That’s a constant battle.”
Andreadis and his scientific brethren generally attribute invasions of non-native species to the increasing global movement of people and products. That’s thought to be how the Emerald Ash Borer arrived, as well as the Asian long-horned beetle, an even more destructive tree pest that so far has not entered Connecticut from Massachusetts, where it’s been for years.
But many now believe climate change could also be playing a role — a prospect that is more troubling. While there is some possibility of controlling the global movement of hitchhiking pests and curtailing domestic invasive movement through actions such as prohibiting the transport of firewood, there is almost no possibility of that when climate change or its accompanying weather extremes are propelling factors.
“That is very true,” said Bill Hyatt, natural resources bureau chief at the Department of Energy and Environmental Protection (DEEP). “As conditions warm, the habitat is going to become less suitable for some native species, less suitable for some established non-native species, more suitable for others. There’s going be influxes of more southerly species, and what that sets up is a pattern of disruption, and any time you have a pattern of disruption it creates an opportunity for non-native, invasive species to gain a foothold.”
He pointed to hydrilla, an aquatic invasive that came to the U.S. decades ago as an aquarium plant. It’s more of a problem in the south, but has come into Connecticut. “It is also one of our concerns,” he said, “that Connecticut would become over time a more hospitable environment.”
Among the newest and most worrisome invasives he and others cited is the Asian tiger mosquito. It can carry Dengue Fever and a painful virus called Chikungunya. It is most suited to tropical areas but has come into Connecticut in recent years.
The latest arrival is the southern pine beetle.
The assault on trees
The beetle hails from Central America, but has been a long-time resident of the U.S. Southeast, where it’s destroyed millions of acres of pine in the last 50 years. It was spotted on Long Island last October and in Connecticut this March.
“It’s been working it’s way north,” said Rutledge, whose specialty is wood-boring insects. “It does seem to be climate-related.”
No one is sure yet what the damage could be or whether it will make it through the winter. It mainly hits a species of hard pine – Pitch Pine – that is sparse in Connecticut. But Rutledge said the beetle has been found here in several other species, including white pine, which is not a preferred host but is the most widespread pine in the state.
The bigger problem, and the problem in dealing with any invasive that damages or kills trees, is the ripple effect. “Everything is connected to everything else,” she said. “Beyond the consequence of losing just that one species of tree, there are severe consequences for things that eat the seeds of the tree, the things that are feeding on that tree, the things that are nesting in that tree.
“It’s ecology; it’s messy.”
Another piece of that messiness is what tends to move in once those trees are gone. Often it’s invasive plants. And that’s becoming a very real threat with the ash tree situation.
Rutledge is in her third year of treating ash trees with bio-controls – tiny, parasitic, non-stinging wasps that theoretically will slow the borers’ spread by killing at least some of them. The wasps arrive as eggs in cylinder-shaped wood bolts or mesh-covered pill containers that she hammers or hangs onto trees. But more than a few scientists working to save the ash trees have called it a “losing battle.”
“I think that what’s going to happen is most of the adult trees will die,” Rutledge said. “The attack that is happening right now is so massive that there’s no way for the wasps to catch up.”
State Forester Chris Martin isn’t holding out much hope either. While trees can be sprayed to combat the ash borer, it’s ongoing and expensive. But so is cutting them down – something that is often necessary because dead ash trees decompose quickly. Their falling limbs then pose a safety threat, of special concern here because so many of the trees line roads.
He’s suggested to municipal tree wardens that they begin to secure funding to spray or cut down their problem trees, and said the state is planning to harvest a stand of ash in Putnam Memorial State Park. “It’s more cost-effective to harvest the trees and use the wood for something beneficial than to hire a tree company to take them down and chip them,” he said.
Martin also has a wary eye on the state’s oak trees, which suffered widespread defoliation this spring from a major return of gypsy moths for the first time in many years. The cause was definitely weather-related – a dry spring that prevented growth of a fungus that keeps gypsy moths at bay. Whether those conditions are related to climate change is hard to know, even though extremes in weather, such as this spring’s lack of rain and last winter’s extreme cold, may be.
The assault on people
That dry spring was also cool, and the mosquito that carries West Nile virus, officially culex pipiens, prefers hot, dry weather. The first mosquito infected with West Nile wasn’t detected by the mosquito surveillance program at the experiment station until July 20 in a sample from Waterford. So far, mosquitoes carrying West Nile have been found in six shoreline towns. The numbers of mosquitoes that carry Eastern equine encephalitis was running about average — but again, no infections so far.
Philip Armstrong, who runs the surveillance program, worries that climate change may change the transmission dynamics of West Nile Virus. “So if you have warmer longer summers, that will increase the duration of time for virus amplification, and that could increase the risk for human infection as well,” he said.
The unknowns are how climate change will affect other parts of the mosquito cycle, such as the birds that carry West Nile. “It’s a very complicated system,” he said. “It’s hard to really tease apart how climate can affect all these many interacting components that are required for virus transmission.”
His wariest eye, however, is on the Asian tiger mosquito — a southern species first picked up in traps here in 2006. Its population spiked in 2013 after a mild winter during which it was found to have over-wintered in the state for the first time. The Chikungunya virus it can carry is prevalent in the Caribbean and has turned up in Florida in recent years. So far all the cases here are in people who have traveled to those places.
“We have every reason to believe that if the climate becomes milder here, and we have warmer, longer summers, it’s going to make it more hospitable for this mosquito to survive and flourish,” Armstrong said. “So I think that is really a concern.”
Weather, if not climate change, is also probably responsible for a bumper population of ticks this summer. While logic might have said that the cold winter would have killed them off, in fact the large amount of snow helped insulate them.
“It also provides moisture, humidity that the ticks need to survive,” said Kirby Stafford, state entomologist and chief scientist in the department of entomology at the Experiment Station.
Adding to the concern is that the deer tick (also called the blacklegged tick) that spreads Lyme disease , is now associated with five pathogens, some of which are turning up more often just outside our borders.
Is there a possibility that climate change could push those pathogens and even other ticks in? “The potential’s there,” Stafford said, citing the Lone Star tick, which is abundant in the southeastern U.S. “It became well-established in Long Island about 10 years ago, but it wasn’t there originally. It is slowly spreading north.”
It seems to have plenty of company.
The assault on land and water
The list of invasive plants clogging Connecticut waterways and strangling landscapes is long and getting longer, and the problems they represent generally are not diminishing. Climate change could make things worse as southern species like hydrilla creep northward, existing species are no longer suited to the environment and conditions stress vegetation, making it easier for invasives to take over.
Invasives love hot weather. They have no natural enemies or diseases that can knock them back. They can out-compete and out-grow native plants.
“They make areas unsuitable for wildlife to live,” said Donna Ellis, senior extension educator in UConn’s department of plant science and co-chair of the Connecticut Invasive Plant Working Group. “They’re certainly having a banner year in some parts of state.”
Some of the worst invaders are mile-a-minute vine. Ellis said a large new patch was found this year in Glastonbury — the second large one to surface east of the Connecticut River. It was treated with a bio-control weevil in July. Purple Loosestrife is being treated with a bio-control beetle, but it has already invaded border to border.
Japanese Knotweed and Oriental Bittersweet are so well established that some argue for just giving up. “I’m an eternal optimist,” Ellis said. “Dealing with it can make a difference in small areas.”
But she said early detection is critical. “We need to learn about the plants that may be problems in Pennsylvania or states south of us. Learn what those are; be on the lookout for them.”
DEEP’S Hyatt agrees. “What we try to do is to look at species that are problematic just outside of our region…,” he said. “It’s so much easier to prevent introduction in the first place than after it’s established in the landscape.”
In the meantime the legislature has appropriated funds to combat aquatic invasive species — $200,000 last year and $180,000 this year. DEEP has made $150,000 of that available each year as grants to help communities fight invasives like milfoil and fanwort. One project getting funding is stocking Candlewood Lake with triploid grass carp, a sterile fish that eats aquatic vegetation.
“We don’t want to eliminate it,” Hyatt said. ”But we want to bring some of these invasive aquatic plants to a reasonable level of control.”
Hyatt said DEEP’s education initiatives, aimed at keeping boaters and fishermen from moving invasives when they move boats and gear from one water body to another, seem to be working. Hyatt wasn’t ready to make the cause-and-effect leap that climate change — already apparent in Connecticut’s warming inland waterways — would mean invasives like milfoil will proliferate further. But, he conceded, if climate change is the cause of more wildlife invasions, it would make controlling them difficult.
Ellis, however, is worried that climate change will result in all kinds of wildlife shifts.
“There may be a greater likelihood of invaders to become established and to now survive in New England, where before they may have only been as far north as the mid-Atlantic region,” she said. “It seems like each year we say, ‘Wow, can it get any worse,’ and something else gets introduced.”
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