Fighting off the invaders

In the Republic, rakes and ropes in hand, citizens tackle the spreading water chestnut

Herb Pearce tosses out a two-sided rake and Squizzle Plekavich holds on to the rope as the two Arlington residents collect plant samples from Black's Nook off Cambridge's Fresh Pond. (Matthew J. Lee/Globe Staff)

A Harvard botanist was just trying to brighten up his garden in Cambridge when he imported some water chestnut from his European homeland in 1877. By the turn of the century, this ornamental plant was choking Cambridge ponds, leaving native plants struggling for survival.

Only in the last decade have ecologists begun pushing for regulation of invasive species, often beautiful but destructive, and begun to battle, among others, the water chestnut.

So under relentless rain last Sunday, Barbara Strell combed the water at Black's Nook, a former inlet of Fresh Pond, using a rake head attached to a rope, sweeping up a slippery tangle of verdant vines and leaves.

"There are so many changes happening now in the environment," she said, water droplets falling from her hair. "As humans, we need to do our part to make sure these habitats don't disappear."

Strell's exercise was part of an ongoing effort to stall the spread of aggressive, non-native plants and restore balance in Cambridge. On that rainy Sunday, she and another member of the Friends of Fresh Pond group led interested locals on a survey of aquatic plants to evaluate the presence of water chestnut and other invasive species at Black's Nook.

The data from grass-roots collections such as this one are reported to the state Department of Conservation and Recreation to track changes over time and determine the health of Massachusetts ponds.

After harvesting their samples, the group retreated to a nearby classroom to identify the plants using magnifying lenses and keys. The results yielded no new invasives, a verdict that Strell called "heartening."

A native plant is one that was present in the environment before human settlement. An invasive plant is introduced via a variety of accidental or intentional events, and often beats out others for access to nutrients. Water chestnut, for example, forms a dense mat and monopolizes sunlight, preventing energy from penetrating a pond's surface. A monoculture forms, causing an unhealthy dearth of biodiversity. Regulations prohibiting the sale of invasive species in Massachusetts went into effect in January 2006.

The results, though, from Sunday's aquatic survey indicated that Black's Nook, which backs up to traffic-packed Concord Avenue, has great water quality given its urban environment, Strell said.

"For all the pollutants and other factors working against it, it's an urban oasis and it would be nice to keep it that way," she said.

Perhaps ironically, human intervention is partially responsible for the pond's health.

A recent weeding program got underway in Cambridge, where several volunteers literally and laboriously weed out invasive species plant-by-plant from ponds.

"I realized from that experience that a half-dozen people can't protect the entire reservation," said Elizabeth Wylde, a Friends volunteer. "It's an unbelievable amount of work."

But longtime Cambridge resident Roger Frymire is on a one-man mission to keep water chestnut from taking over, proving that a single person can make a difference.

"I'm eradicating water chestnut in an entire sub-watershed of the Mystic River," he said. After committing to the project nine years ago, he realized there were large ponds inundated with water chestnut, and pulled 30,000 plants in 10 days.

In a small kayak with a blue recycling bin strapped to the front deck, he tugs and disposes, counting as he goes.

Another invasive culprit is the vibrant purple loosestrife, a hardy Eurasian wetland species introduced 200 years ago. In her own project, Wylde combatted its spread by introducing a beetle that eats only loosestrife. "Introducing a non-native species to combat another non-native species is very risky," Wylde said. But so far, in this case, it has worked.

The stories of how invasive species were introduced to this area are as varied as they are anecdotal. Purple loosestrife was once planted along interstate highways for beautification purposes, said Grenelle Scott, a Cambridge resident and survey participant.

Animal species can also be invasive. According to Wylde, house finches were natives of the Southwest, until they started being sold as pets due to their pleasant songs. But when keeping a migratory bird became illegal, some people released their finches, which thrived in the East.

Another notorious non-native? Garlic mustard. "It's really dangerous," said Strell, "because it's allelopathic, meaning it secretes chemicals to inhibit the growth of adjacent species."

A common clover found in lawns today was dubbed White Man's Footprint by Native Americans, because they watched it spring up in the wake of European settlers. (A database of New England invasive species is available at IPANE.com.)

But if purple loosestrife is lovely and clovers are common weeds, why is it so important to eradicate them?

Wylde said it's hard to come up with a definitive answer.

"These ponds have been here a long time, and there is an inherent aesthetic that would be lost if the non-native species took over," she said. "It affects what animals will be able to exist here, and it makes the ecosystem less stable and vulnerable to collapse."

Anyone who ever took a biology class knows that one thing in nature affects everything else. If certain plants disappear, certain animals that depend on them will also leave. Insect populations could grow out of control, wreaking massive damage on vegetation and annoying the human population.

"So often, you never know the usefulness of something until it's gone," said Strell.

There is also a practical and immediate reason for Frymire to continue trashing water chestnuts: Their dead fruits, or seeds, are 1- to 2-inch ashy black stars with four spiked horns, and are viable for 12 years. They pose a danger to dogs that get the seeds stuck in their paws, and owners can get hurt trying to remove them.

"I have a burr stuck in my thumb right now," Frymire said.

Frymyre plans to continue battling his floating nemesis at Black's Nook until it's gone.

"Even though it's hard to prove, the health of the water bodies where I've pulled has changed drastically," he said, "and the shoreline is no longer lined solid with seeds. I hope that encourages other people to take on similar projects."