Invasive Plants Spreading As Climate Warms, Study Says

A woman walks along a trail at Walden Pond in Concord, Mass., June 2007. A Harvard study focused on invasive plants around the pond. (AP Photo/Elise Amendola)

BOSTON — As the climate continues to change, non-native plants — especially invasive ones — could become even more widespread and destructive, according to a new Harvard study (PDF).

The researchers found that some invasive plants have begun to flower earlier in the year as average annual temperatures have gone up.

Early growth appears to give them a chance to dominate an area and destroy surrounding wildlife habitat, as well as cause other environmental problems.

It is not clear why some invasive plants flower sooner than native ones as the weather warms.

But one possible reason, according to the study’s author, Charles Davis, an assistant professor in Harvard’s Department of Organismic and Evolutionary Biology, is that by growing bigger earlier, invasive plants prevent native species from getting sun.

“Maybe it’s because these things are getting such an early jump-start on the season that they’re producing leaves much earlier,” Davis explained, “so they have a competitive advantage and they’re shading out or excluding native species that are in this part of the world.”

In some instances — such as in the case of purple loosestrife, a fast-growing weed that has become prevalent in parts of the state — flowering is occurring three weeks earlier than it has in the past.

The study focused on plants around Walden Pond, where the average annual temperature has increased by about four degrees Fahrenheit since the mid-1800s.

But Davis said his findings are probably also applicable to the rest of New England and to parts of Europe and Asia that have a similar climate.

“To what extent, though, we’re able to scale or apply these results to other parts of the world, we really just don’t know yet,” he added.

Invasive plants and other non-native species can have devastating impacts on the environment. They can disrupt ecological systems, cut off waterways, displace native species, and interfere with agricultural efforts.

But Davis said there is a benefit to knowing which invasive species are likely to thrive as the climate changes: people can develop better conservation strategies in an effort to keep ecosystems more balanced and protect them from non-native invaders.

“We can nip those problems in the bud, so to speak,” he said.

The Walden Pond area has become a valuable source of data for climate change research because Henry David Thoreau kept detailed, meticulous records on vegetation around the pond — including information on flowering times — dating to the 1850s.

Using the same data, Davis and scientists from Boston University found in a 2008 study that roughly a quarter to a third of the plant species documented by Thoreau have disappeared.

Davis believes climate change is also responsible for that phenomenon, as well as for his finding that familiar plant species such as lilies, orchids, violets, roses and dogwoods are dying off around Walden Pond.

The current study appears in the journal, PLoS ONE. Researchers from Boston University and Duke University also contributed.