Within the mint-green walls of the Kenton Firehouse in north Portland, more than two dozen people are giving up their Wednesday supper hour to sit in folding chairs and snack on frosted cookies. There are young couples and small children and quite a few gray-haired elders, taking turns sharing two things they have in common: their north Portland neighborhoods, and their interest in trees.

“I live in Kenton – I was born in Port Angeles – and the alpine fir is my favorite tree, because it’s kind of unusual,” says one man.

“I’m from New York City, but I live in Kenton now, and my favorite tree is whatever one I’ve seen most recently,” says a woman.

Another man, from Arbor Lodge, likes cedar for its feathery bark. A Kenton man votes for the katsura tree because it smells like cotton candy. An Arbor Lodge woman can’t think of a favorite tree but knows she can’t stand mountain ash, “because my dad made us go out and pick the berries up as kids, and they made such a mess.”

“I’m from Minnesota, and I live in St. Johns,” says a woman across the room. “And as far as trees go, well, I like them all.”

We’re all here tonight because we’ve signed up with a local nonprofit, Friends of Trees, to purchase discounted trees and plant them around north Portland. I first heard of the 16-year-old organization last fall, when a flyer arrived in the mail announcing the neighborhood’s January planting. Affordable trees, approved by the city, planted by a team of volunteers – this sounded like a deal to me. So it was that three months later I found myself at the firehouse, shuffling through papers describing available trees and squinting through the dimness at a Friends of Trees slide show.

“Street trees are picked to be the biggest for that width of planting strip, to maximize the benefits of trees,” announces Jim Gershbach, the Friends of Trees volunteer conducting the slide show. Tree choices are dictated by the size of the available planting strip, that grassy chunk of turf between sidewalk and street. The skinniest strips are just 2.5 feet wide; the most expansive are more than 8.5 feet.

“Ah, here we have the Japanese snowbell,” Gershbach says, flicking up a slide of a small, bushy tree covered in soft white down. The crowds murmurs appreciation. “This is the single most popular tree we plant. You can see why; in the spring it’s covered with these showy, dainty flowers. But it’s also fast-growing and disease- and pest-tolerant.” And it will fit, happily, in a strip only 2.5 feet wide.

Before a planting session, city tree inspectors check out the lay of the land and dab white paint on the curb to indicate the best planting spots. Dig in the wrong spot, and you might hit a sewer line; plant the wrong tree, and in 50 years you might have an overhead-powerline snarlfest.

The trees themselves, bought from local nurseries stretching from Boring to McMinnville, are selected for their beauty, toughness, growth rate and ease of care. Friends of Trees pays full price, says executive director Scott Fogarty, but because so much of the nonprofit’s work is done by volunteers, donations can reduce the cost to neighborhood homeowners by as much as 50 percent.

“There’s multiple benefits to planting trees,” says Fogarty. “Of course, there are several major environmental benefits; the top three are carbon sequestration, stormwater reduction and shade. Trees pull carbon from the air and produce oxygen; they’re one of the reasons Portland has such good air. Trees also absorb water, reducing the amount going into the drains. And they provide great shade in the summer, keeping us cool and reducing energy levels.”

But Fogarty points out that, as demonstrated by that chatty firehouse meeting, organized tree plantings do more than help the planet. “They’re really a community-building event,” he says. “Digging the holes and planting with other volunteers, you get to meet your neighbors and other people from the neighborhood.”

With a geographic planting zone that ranges from Gresham to Tigard and Vancouver to Wilsonville, Friends of Trees is the chief tree planter in the Portland metropolitan region. The nonprofit has some 2,000 volunteers and has planted approximately 300,000 trees and native plants over the past 16 years.

“In San Francisco, they plant about 500 trees a year,” says Fogarty. “Here, we do a little bit more than 2,000 trees a year, on average.”

But, Fogarty adds, racking up a high tree count isn’t really the chief goal of Friends of Trees. Fall through spring, volunteers aren’t just given shovels and tender young trees to stick in the ground; they’re taught how to plant them properly and how to care for them. Come summer, work crews (which include teens hired from juvenile-detention centers) go around checking on water levels and mulch.

“We have a really good tree-survivability rate, in the 90th percentile,” says Fogarty. “It’s not just about the act of planting the tree itself; it’s about the residual community benefits.”

On the wall of the firehouse, Gershbach is showing slides of hornbeam and tupelo trees, their leaves turning yellow and red. “Lots of people, when they want fall color, plant a maple tree,” says Gershbach. “But 20 percent of Portland’s trees are maples already, and you’re not supposed to have any one type of tree exceed 5 percent in your urban forest. Like the Dutch elms, remember?”

Everyone nods, aware of Dutch elm disease and its devastating effects on the nation’s elms in the mid-20th century. “They were planted everywhere and made gorgeous crisscrossing street arbors,” Gershbach continues. “But they were a recipe for disaster. Almost every year, because of global trade, we get new tree pests in this country. So it’s good to think ahead about pest resistance and tree diversity.”

People take notes and whisper to their neighbors. New hybrids. Tree diversity. Who’s going to be home enough this summer to water their thirsty trees? Will the young parents get trees that smell fabulous to please their kids, even if they hate cleaning up fallen fruit and leaves? And how many of us will still be around, decades from now, to enjoy the trees planted this month?

We came because we wanted trees; we got education and community as well. In the long run, that’s what Friends of Trees is all about: the idea that the trees we take care of now will, eventually, take care of us.