WEST ROXBURY — It appears to be the chiseled handiwork of an ace axman: Tree after tree along the water’s edge in Millennium Park felled by a clean v-cut.
But it is no rogue Christmas tree cutter. It’s beavers.
The furry rodents are making a comeback throughout the state, in large part because of a more-than-15-year ban on trapping them. Their distinctive log-and-branch architecture is dotting landscapes and damming up streams and culverts from woodsy bogs to big-box-store parking lots.
Though the beavers have done little real damage yet in Millennium Park, there are few places in the state where their impact is more stark. More than 80 trees have been chewed or felled along a popular walking path — and many more appear down in the adjacent wetlands and in the thick tangle of woods near the canoe launch on the Charles River.
“I’ve never seen such activity,’’ said Patty Courteau of West Roxbury as she walked her dog in the 100-acre park, a sprawling complex of athletic fields, wetlands, and a playground behind West Roxbury High School that was built atop an old landfill.
Beavers were once intensely hunted in Massachusetts and disappeared from the state by the mid-1700s because of trapping and deforestation as land was cleared for farming. Trees grew back and by 1928, the first beavers in nearly 180 years were spotted in West Stockbridge in the Berkshires. By the 1930s, a restoration program began with three New York beavers introduced into Lenox, according to Laura Conlee, furbearer biologist with the Massachusetts Division of Fisheries and Wildlife.
With few natural predators, the beaver population grew so quickly that state officials established a hunting season in the early 1950s. But public sentiment against certain types of traps for animals grew, and in 1996, a state ballot referendum banned most types of traps.
“Following that ban, the beaver population expanded drastically,’’ said Conlee. By 2000, there were about 70,000 beavers in the state, drawing enough complaints from the public that state officials allowed communities to grant emergency permits to kill a limited number of the animals if they were causing severe flooding or public safety problems. There is also a limited trapping season when beavers can be caught using more humane traps.
State officials used to estimate the number of beavers based on how many were trapped, but they no longer have a good estimate since communities began issuing the emergency permits. All they know, Conlee said, is that the beavers are expanding to the east and south.
“When they get to Millennium Park, they are pretty east, obviously,” Conlee said. Beavers have also shown up in Plymouth and Duxbury in the last five years, and are beginning to get into cranberry bogs, where they could interfere with water-flow devices, she said.
Conlee said there have not been many complaints yet, but there are likely to be more if the animals continue moving to new areas.
Beavers tend to spread out over generations as the young look for a place of their own. With so many animals already populating prime areas, many beavers are forced to live in places they would not have considered previously. Often, that means living closer to humans and causing damage, such as damming up a culvert by a parking lot or a septic system — or even building their homes in a popular park.
“We get a lot of calls,’’ said Conlee. “A lot of people look at beavers as huge pests . . . We get a lot of people concerned that the trees are going down.”
But Conlee said beaver-created wetlands are incredibly productive areas for other wildlife, from birds that use the dead trees to young fish. “They really are valuable,’’ she said.
In the late fall, beavers are busy taking down a lot of trees for winter food: branches and twigs to store in their lodge for the winter. They favor poplar and aspen trees and can take off the entire top of a tree to store in their lodge.
At Millennium Park, the beavers’ handiwork is everywhere, but they are not causing harm, said Jacquelyn Goddard, a Boston parks department spokeswoman. “They don’t flood pathways,’’ she said.
For walkers, many with dogs, the felled and gnawed trees are an interesting footnote on a nature walk. The beavers began showing up en masse about two or three years ago, walkers said, and although they can be difficult to see, at around 5 p.m. they can be heard gnawing and splashing. Occasionally, a tree is heard falling down.
“I’ve still never seen a beaver,’’ said Tom Daly of West Roxbury, walking with his wife. “But I see their work everywhere.”