Greg Mosman, the chief arborist for the city of Boston, is both a tender botanist and a thrill-seeking adventurer…

This is Greg Mosman’s favorite spot. 24 acres of ancient, majestic trees guard one of the most magnificent centerpieces in Boston, Massachusetts – the Boston Public Garden. It’s a living monument that symbolizes Boston’s appreciation for aesthetic beauty, and is a testament to the botanical talents of many generations of Boston’s great arborists, the freshest of which is Greg Mosman. From where we sit admiring the view, it’s hard to notice the growling and screeching of Boston traffic that moves just a few meters away.

“This is my favorite spot,” Greg Mosman said to me, “when I’m at work here, I often forget that.” Greg Mosman is an urbanite who fell in love with trees – he’s both a tender botanist and a thrill-seeking adventurer. In addition to being the Chief Arborist for the City of Boston, he’s also an avid Tree Climber. Mosman maintains 3,600 total acres of a smattering of trees across the city, including those in the Boston Public Garden. He prunes and primps, shapes and heals more than 200 different varieties, each with its own medley of needs. Unlike most arborists, he opts not to take the bucket truck into the canopy. Rather, he uses ropes and levers, carabiners and brute strength. Today, he’s dressed the part of a hard-core outdoorsman – adorned with Carhart pants and sticky rubber Lowe Alpine shoes. With him, he’s brought a pile of heavy, clanking tree-climbing gear.

Mosman didn’t discover his interest in trees until college when he was studying to be a golf course manager at UMass Amherst. A friend introduced him to tree climbing and as he got more into the sport, his interests grew taller than turf. He dropped out of UMass, and began studying horticulture at Essex Aggie College. To stay closer to the canopy, Mosman decided to become an arborist.

Surprisingly, Mosman’s love for trees never left the city. Adorned in climbing gear, he seems like a misplaced logger, but he will take a Red Oak tree in the park over a giant Douglas Fur in the forest any day. “Greg would rather drive up to a tree, plop down his gear and start climbing,” Andrew Joslin, his climbing partner said. “He hates hiking to a tree.” In fact, Mosman’s philosophy is that of a true city arborist. He cares for his trees not as a population, but individually – it’s about the tree, not the forest. Only in the city can an arborist take such time and precision with every tree.

Seven years ago, Mosman applied for a job as Chief Arborist for the City of Boston. “I was kind of surprised I got it,” he said. Boston, a city known for its myriad old, beautiful trees, is one of the more prestigious jobs among arborists. However, when you talk to Mosman about trees long enough, his appointment makes sense.

Three years ago, Mosman and Joslin met through a tree climbing website. They began climbing together regularly and eventually decided to form the Boston Area Recreational Tree Climbers (BARC), an organization for both novice and experienced climbers. Through BARC, they ran climbs for several groups of school-aged kids but were shut down by park rangers. “They thought it was too dangerous for kids,” Mosman said, “when actually it’s safer than rock climbing when you do it right.” As a result, they started getting some negative attention from a reporter for the Jamaica Plain Gazette, who implied in an article that Mosman and Joslin conducted unsafe, illegal climbs around the city. “It just couldn’t have been any farther from the truth,” Mosman said, “he didn’t even bother interviewing us before he published it.” Despite the reporter’s eventual retraction, BARC fizzled. Since then, Mosman has been struggling to keep tree climbing legal in a few pockets around the city. “Without Greg, no one would be allowed to climb in the city at all,” Joslin said.

As we walk through the Boston Public Gardens , Mosman reaches up and grabs the budding branch of a tree. He asks me to touch one of the buds – it’s sappy and sticky. “That’s how you know it’s a Weeping Cherry,” he said. “Apples leaf before they flower, Cherries flower before they leaf.” Just by looking at a tree, he can tell its life history. Mosman can tell that a scar on a tree’s trunk happened ten or thirty years ago. If a tree is misshapen, he can tell when and where there were drainage issues in the soil. Joslin, who is also incredibly knowledgeable about trees, claims that he learned virtually everything he knows about trees from Mosman.

He points to another tree that seems to have been rammed into the trunk of another – it looks like it’s growing out of a collapsed, brown birthday cake. It’s a Camperdown Elm that has been grafted onto an American Elm. Every few decades, a new disease or pest will come around and kill off a certain variety of tree – the American Elm was killed off by Dutch Elm disease, but before that, Chestnut Blight Disease killed all the Chestnuts. Currently, the Asian Longhorned Beetle, which primarily prays on Norway Maples, is on Boston’s doorstep. Worcester, just an hour west, already cut down nearly 10,000 infested trees. Mosman said that he already has a game plan should the beetles infiltrate Boston. “Cut down all the host species,” he said, “if you leave a single one of them, you’re almost guaranteed to have a big problem on your hands.” When Worcester began to see signs of an infestation in 2001, Mosman advised them to do just that, but they didn’t listen. 75-85% of their tree cover was Norway Maple, Boston’s is only 44%. “We’re ready to cut down all of the Norway Maples at the first sign of infestation,” he said, “luckily, it won’t be as devastating to us as it was for Worcester.”

As the Chief Arborist for Boston, Mosman wears many coats, most of them foreign to the average urban-dweller. Rather than worrying about the economy, Mosman worries about the next arboreal epidemic. Dead limbs over roads always need to be removed, park trees always need to be manicured. As long as there are trees in the city, Mosman will climb them for a living.