Mike Nichols is covered in dirt. He’s kneeling in the bed of a landscaping truck parked on a street in East Boston. Sitting next to him is a small, leafless maple tree. The sapling is about 6 feet tall and its skinny trunk is only 3 inches wide. But with all the wet soil packed around its roots, it weighs between 300-400 pounds.

“Let me get my guys to help me out and get the tree down,” Nichols says, hopping down from the truck and waving over his two assistants. The three men work for the landscaping company Hartney Greymont, and today they’ve been hired by the city of Boston to remove two dead trees and plant new ones in their place.

While his assistants stand the tree upright, Nichols starts up a small fork lift and gently scoops the tree from the truck. He drives the sapling to the hole his team dug nearby and, very gently, puts it down.

He says he's "trying to give it as much chance of survival" as possible.

Tree survival is especially important in a place like East Boston. The neighborhood has the lowest tree canopy coverage in the city, which means that during the summer, it also has some of the worst hot spots.

Urban heat kills about 600 Americans every year, and sends another 65,000 to the emergency room, according to a recent report from the Urban Land Institute. Climate change is going to make these problems worse, the report's authors write.

"In the Northeast, we can expect approximately 650 deaths per year [from heat] by 2050," they wrote in the report.

Mike Nichols puts the finishing touches on a hole inside Prescott Square Park in East Boston. A new tree will be planted there. (Jesse Costa/WBUR)

Given that risk, Boston — like many cities around the country — has been reexamining its relationship with its trees, and thinking more strategically about planting and preserving them. In the past, despite spending about $900,000 annually on street trees, the urban forest has been a bit of an afterthought.

“Trees are often viewed as window dressing. But in reality, they’re this really fundamental infrastructure that has life or death consequences, especially as our cities are heating up more and more,” says Ian Leahy, vice president of urban forestry at American Forests, a national conservation organization.

Urban trees have benefits beyond shading and cooling. They clean the air, sequester carbon, reduce noise pollution and help prevent flooding by absorbing stormwater. Plus, studies show that places with a lot of trees have lower crime rates and fewer traffic accidents.

“All the research shows trees improve retail sales, improve property values, reduce attention deficit disorder symptoms, improve academic performance,” Leahy says. “[Trees have] all kinds of psychological impacts.”

'Great,' you might be thinking, 'let’s plant a bajillion trees.' Unfortunately, the solution isn’t that simple; a lot of street trees don't make it more than a few years in the big city.

“It's tough to be a baby street tree because your roots are really little. And the summers in Boston are quite hot, so drought alone can kill them,” says Andrew Trlica, who recently earned an urban biogeochemistry doctorate from Boston University. His dissertation focused on the life and death of street trees in Boston.

Mike Nichols, Tomas Cardoso and Romeo Gonzales remove a young tree from their truck. (Jesse Costa/WBUR)

To be an urban tree, especially one planted in a metal grate on a sidewalk bordering a busy street, is to have the odds stacked against you.

“Cars run into them. Bikes getting locked to them is really surprisingly damaging when they're little like that because their bark is kind of wimpy," Trlica explains. "Road salts that can wash in there are hard on their roots. Dogs peeing on them can be too much nutrients. It's just a tough environment."

Hazards abound: gas leaks, utility work, foot traffic, car collisions, snowplows. On the bright side, Trlica finds that street trees grow a lot faster than their country cousins because they’re exposed to more light. As another recent study puts it, street trees “Live Fast, Die Young.”

Trlica says he began to wonder: If city officials want to increase tree canopy cover to deal with climate change, should they focus on planting new trees or helping older ones survive? To figure it out, he looked at two scenarios for Boston: spend the next two decades planting saplings in every available sidewalk location, or spend the time reducing the mortality rate of older trees by 50%.

For Trlica, the answer was clear. Yes, Boston should continue planting trees, but the real canopy payoff will come from preserving bigger, leafier ones.

Cardoso and Gonzales remove the burlap covering the roots of the tree. (Jesse Costa/WBUR)

Chris Cook, Boston’s chief of environment, energy and open space, says tree preservation is top of mind as the city begins designing a master plan for its urban forest.

“Planting in the public realm with street trees can be enormously complicated because there are a lot of conflicting interests — there’s utility infrastructure, there’s accessibility concerns — and then there's just the actual physical space [limitations],” he says. “So, the more we can care for the existing trees in our parks [and on our streets], the better off we are.”

The plan itself should be released sometime in 2021, he says, though the results of a recent canopy coverage study the city conducted last summer could come out sooner.

“This will be the first time in a good amount of time that we’ll actually have an up-to-date assessment of tree canopy,” Cook says. “We think [the study results] will show us really key areas within the city that we need to focus on.”

The last time Boston conducted a Light Detection and Ranging (LiDAR) study — a process that uses drones to create a three-dimensional map of canopy coverage — it found that the average canopy cover across the city was 27%. But the shade was far from even. Places like Roslindale, Mattapan and Hyde Park have more than 30% canopy coverage, while some areas of Dorchester and South Boston are below 10%.

The above graphic shows the current tree canopy in Boston. Deeper green colors represent a more developed canopy. (Courtesy University of Vermont)

The above graphic shows the potential for tree canopy in Boston. Deeper red colors represent areas with the most potential to increase tree plantings. (Courtesy University of Vermont)

The city’s 2014 Climate Ready Boston plan calls for 35% canopy coverage by 2030, though Cook is quick to say that “total tree canopy — just like the individual numbers of trees — isn’t quite important as looking at the vulnerabilities different neighborhoods have with canopy.”

“Tree equity” is a term he and others in the urban planning world throw around a lot these days.

"The areas where urban canopy is the scarcest tend to coincide with neighborhoods that are low-income, minority neighborhoods, and historically red-lined areas,” says Deanna Moran of the Conservation Law Foundation. “And so, some of our most at-risk populations — populations that are going to be particularly burdened by climate change and other issues — are also the ones not benefiting as much from the canopy.”

Cook says this research is at the heart of the city’s urban forest plans.

“You look at a neighborhood like West Roxbury that’s one of the leafiest neighborhoods in the city of Boston — well, is it better to plant a whole bunch of trees [there] just because you have the opportunity to do so?" asks Cook. "Or is it better to work hard and find planting locations in a place like East Boston, where it might have more health benefits to the residents there?"

The second choice, he says, will pay dividends "not only on a climate adaptation perspective, but also from an equity perspective."