LEBANON — Lebanon’s most heavily paved precincts could stand for a bit of rewilding, members of the city’s Tree Advisory Board say. To mitigate the impacts of extreme heat, the city should break up stretches of pavement with trees.

Where heat-absorbing asphalt dominates and trees are scarce, temperatures soar in areas researchers have dubbed “heat islands.” Placing trees in urban areas can cool down the impacts of extreme heat by offering shade and absorbing heat from the sun that would otherwise warm up the neighborhood even more.

Last spring, the Tree Advisory Board started mapping heat islands across Lebanon. Member Charlie DePuy, who has a background in urban planning and conservation, marched down the street on the hottest days of summer, collecting temperature data from a pocket-sized thermometer he had connected to his phone. Soon he was joined by a platoon of Lebanon High School students, who were able to translate the data the team collected into a series of maps of the city’s heat islands.

These hot spots — which can range in size from a superstore parking lot to an unshaded length of sidewalk — become more important to identify as higher-than-average summertime temperatures increasingly pose a health crisis. Prolonged exposure to extreme heat can lead to heat stroke, cramps and nausea, among other symptoms. New Hampshire’s 2021 climate assessment, which identifies the effects of climate change, predicts more days of extreme heat each year.

“It’s pretty obvious that you walk around the street and it’s going to be hot, and that if you walk under a tree, it’s going to cool off,” DePuy said. But he and fellow board member Mary Maxfield felt that gathering data brought the issue home: “It helps to make it visible, particularly on a map.”

The Lebanon Department of Human Services reported to the Tree Advisory Board that it is most concerned about the impacts of extreme heat in downtown Lebanon and West Lebanon, especially in older buildings containing many apartments in low tree-density, high population-density neighborhoods.

Lower-income residents are more likely to live or spend time in hotter areas — near or in heat islands — the Tree Advisory Board reported to the City Council last month. To supplement the raw temperature data, Maxfield, a former Lebanon High School biology teacher, interviewed more than 100 Lebanon residents about their experience with extreme heat.

“Some people that felt they were immune from the ravages of heat because they were able to go into a cool house if they needed to, or you can go into the woods at certain times of day,” Maxfield said. “But there are some people — those that spend a lot of time at bus stops, the unhoused, people that live in their cars — they are in dire straits when it comes to extreme heat.”

Any tree ordinance that Lebanon adopts should take into account “the human piece,” Maxfield said. “If you ever go to Walmart and see the bus stop there, it’s pure asphalt and cement against a big white wall. People might have to stand there for half an hour on the hottest day of summer.”

Planting more trees is the best way to deal with urban heat islands, Lebanon Mayor Tim McNamara said. But it requires careful planning.

That’s why the Tree Advisory Board was created in the first place, he added: “We wanted to get some advice on how to proceed with tree planting going forward.”

McNamara’s goal is to draft a tree planting budget that can be voted on in December.

The budget will guide a long term tree planting — and replacement — plan.

“As we all know, trees don’t live any longer than we do, and you have to plan for that,” he said.

The ordinance should take into account where to plant, with an emphasis on the urban areas identified by the Tree Advisory Board, and on what species to plant.

Successfully planting trees in urban areas means taking into account a tree’s resistance to things like road salt. Trees like cedars and birches do well in higher-stress environments.

Cost is a consideration, too.

“Obviously, to get the maximum bang for your buck, you’re going to be planting smaller trees. If you’re looking to plant a 12- to 16-inch maple that’s 40 feet tall, that’s a $20,000 investment,” McNamara said. A 14-foot tree is less expensive: “The cost of getting that tree in the ground is probably more like $3,000 or $4,000. So you can plant a lot of smaller trees for the cost of one big tree.”

Big planter boxes, called “biocells,” help with “street planting,” a term used by arborists and planners to describe placing trees in the middle of swaths of pavement.

“They prevent compaction from surrounding asphalt, and give the tree roots a place to expand into,” McNamara said. “And they seem to be pretty successful.”

Frances Mize is a Report for America corps member. She can be reached at fmize@vnews.com or 603-727-3224.

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