PORTLAND — For years Ellen Murphy got used to seeing a swath of large linden trees across the street from her Park Street residence, but this spring the trees were taken down to make way for an expansion project on State Street.

“Judging from the size of the stumps left behind — some of which are 2 feet in diameter — they had stood in that spot for decades. I’d say some of them were about 20 feet high or more,” Murphy said of the mature lindens that used to line a parking lot at Gray and Park streets. Their removal was part of an Avesta Housing project at 75 State St., an independent and assisted living facility.

New rules under consideration by the City Council may help protect trees like those lindens. The Heritage Tree Ordinance, which the council will vote on Aug. 3, would “discourage the removal or extensive pruning of Heritage Trees located in historic districts of the City of Portland on public and private property and to replace the valuable ecological services such trees provide should they be removed.”

The city estimates it would cost around $41,000 to implement the program because a part-time tree inspector would be needed, as well as a work vehicle, a computer, supplies and a phone.

Heritage trees are defined as oaks, maples, pines or spruce that are at least 24 inches in diameter; ornamental trees of at least 12 inches in diameter; or any native tree on the endangered list. Property owners would be able to remove those trees if they are in poor health, dead, damaged or infected, but if a tree is removed for any other reason, a permit is needed. Jeff Tarling, the city arborist, would have the authority to approve the permit and decide how many new trees would be required to mitigate the loss of the heritage tree. Property owners could alternatively provide funding to the Tree Trust, a pool of money used by the city to plant and maintain trees.

“The goal of the program is the protect mature trees, mature heritage trees, ” said Councilor Spencer Thibodeau, chairman of the council’s Sustainability and Transportation Committee, which voted to unanimously support the proposal May 20. “There was concern there was nothing that would prevent someone from cutting down one of these trees outside of the site plan review part of the Planning Board process.”

The rules, if approved next month, would apply to historic districts along Congress Street from Deering Avenue to Franklin Street, the neighborhood around Deering Street, Fort McKinley on Great Diamond Island, House Island, the old How family properties on Danforth and Pleasant streets, a section around India Street from Middle Street to Cumberland Avenue, Portland Company on Fore Street, Stroudwater, part of the Portland Waterfront/Old Port, the West End and the University of New England campus on Stevens Avenue. A large section of Munjoy Hill has also been proposed as a historic district.

Elissa Armstrong, a resident of Spruce Street, supports the idea.

“I hope it is something that can be tried in the historic district and eventually be available to the whole city because saving trees is (a) really important part of our carbon foot print reduction,” she said. “I would also like to see going forward at some point, to reduce the size of the trees designated because we really need to save all the trees.”

Other West End residents, including Allen Armstrong, Katherine Gilbert and Jennifer DeFillipp, told the committee they were supportive of the program. Gilbert and DeFillipp, both residents of Winter Street, said they have lost mature trees on the street to development.

George Rheault of West Bayside spoke against the proposed rules, saying the city has more important things to deal with and such an ordinance could prove to be a “needless hurdle” aimed at stopping development.

Murphy is not sure whether the Heritage Tree Ordinance, had it been in place, would have saved the linden trees at Gray and Parks streets, but she is concerned about sustainability after any tree removal.

Citing a 2016 United Nations report, she said a mature tree can absorb up to 150 kilograms (roughly 330 pounds) of carbon dioxide.

“The correct placement of trees around a building such as 75 State St. can help to reduce carbon emissions by conserving energy,” Murphy said. “The UN report estimates this can reduce the need for air conditioning by 30% and reduce winter heating bills by 20-50%. Trees increase urban biodiversity by providing plants, birds and animals with habitat, food and protection.”

A number of other municipalities have adopted similar rules, but Portland, Thibodeau believes, would be the first to do so in Maine.

“It’s a really exciting opportunity for us to take the next step of protecting mature tree canopies especially on the peninsula where we have seen development and some of these trees have been taken down,” Thibodeau said.

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