Invasive Plants Spreading in Vt.

Ever had phytophotodermatitis? Blisters, reddened skin similar to second-degree burns, terrible discomfort.

The kicker is, it’s caused by a relative of the carrot. And it’s a newcomer to Vermont.

Poison parsnip is a plant with broad, low leaves and yellow flowers on a tall stalk. Touch the sap and expose it to sunlight, and — ouch — it burns the skin.

There are several plant newcomers in Vermont these days, and many, such as poison parsnip, are considered noxious weeds. Some scientists contend climate change will help those weeds thrive, while making it harder for native species to compete. Others researchers, however, aren’t convinced.

Tim Schmalz, a plant pathologist with the Vermont Agency of Agriculture, Food & Markets, said he’s skeptical of studies that claim particular weeds will spread as the climate changes.

“There are a lot of things that may happen or may not happen,” said Schmalz. “It’s very hard to predict environmental change on that scale.”

On the other side are scientists such as Lewis Ziska, a plant physiologist with the U.S. Department of Agriculture, who said weeds in general will be more robust and more plentiful in a warmer world .

“The factors in climate change that are relevant here are really related to carbon dioxide and temperature. In that context, and I’m speaking in very broad terms, what we see is that weeds tend to respond more to the carbon dioxide that has already occurred and is projected to occur in this century,” he said.

Ziska said to be on the watch for weeds that are already major problems in the South: kudzu, pale swallow-wort, Japanese barberry, and giant hogweed, which causes phytophotodermatitis many times worse than poison parsnip. Ziska also said to expect more poison ivy.

Several state agencies have weed-control programs. The Agency of Transportation, for example, times its roadside mowing to kill poison parsnip before it begins to produce seeds. But according to Schmalz, at least in the Agency of Agriculture, Food & Markets, funding is tight and weed control competes with other priorities.

Until recently, state officials had fewer invasive plants to worry about. Vermont’s cold winters kept many of them at bay.

“What we’re seeing is not just for weeds, but for a range of different animals and a range of different plant species, that one of the things that keeps species where they normally are is cold winters,” said Ziska. “As the winters warm, it expands the range that species can move into.

“Not every species takes advantage of that. Oftentimes, the species that do take advantage of that are invasive species. Those are the species that tend to move very rapidly when there’s a shift in the climate.”

For example, kudzu, a fast-growing vine that covers forests and farm fields in the South, has been found in Massachusetts and Ontario.

When Massachusetts state officials first visited the property in Needham that had a kudzu infestation, they estimated the plant covered 150 square feet. When they returned a week later, the plant had grown noticeably.

“Seeing it like that gives you an idea of how bad it could get if you let it go,” said Jennifer Forman-Orth, state plant pest survey coordinator with the Massachusetts Department of Agricultural Resources.

The site in Needham is one of four kudzu infestations government agencies are battling in Massachusetts. While they are small compared to the acres of kudzu-choked forests in the South, these patches represent the forerunners of an expanding threat. A 2010 study by researchers at Princeton found that kudzu’s bioclimatic envelope — the conditions in which it can survive — will include Vermont by the year 2100.

Paul Marangelo, a conservation ecologist with The Nature Conservancy, said it’s difficult to determine which weeds will show up and when — and what effect they will have.

“It’s a little more theoretical than actual at this point,” said Marangelo. “It has to do with anticipating that as the climate warms, natural communities are going to change in unpredictable ways. Some of the changes in the climate might provoke more disturbance events like fires or some other phenomenon that disturbs natural communities. Those disturbances can provide opportunities for invasive plants to come in and get a foothold and start to grow.”

Invaders of concern, Marangelo said, include mile-a-minute vine and Japanese stilt grass, both of which deprive surrounding plants of sunlight.

“There are a bunch of species that are poised to make their ways up this way, and they’ll probably do a little bit better in Vermont than they would have otherwise,” said Marangelo.

Vern Grubinger, a professor at the University of Vermont agricultural extension office, said that it’s difficult to pinpoint a single cause for the rise of invasive species. Some weeds and diseases get transported on farm equipment or manure.

“It’s just hard to say. Is that temperature or more movement of plants and seeds?” asked Grubinger.

Rather than one force, Grubinger said it’s the synergy of multiple factors that is scary.

“To me the biggest concern is the combination of the shifting change and this intense commerce, moving things around globally, that together elevate uncertainty and risk for new things arriving,” he said.

Grubinger said he is concerned that climate change raises so many new concerns to farmers that they might get overwhelmed.

“Farmers can’t deal with all of this all at once,” he said. “They need to prioritize. In the case of some of these invasives, it may mean that you have to change your crops if you’re not willing to do the management that’s necessary.”