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SEATTLE — Across the U.S., cities are struggling to balance the need for more housing with the need to preserve and grow trees that help address the impacts of climate change.
Trees provide cooling shade that can save lives. They absorb carbon pollution from the air and reduce stormwater runoff and the risk of flooding. Yet many builders perceive them as an obstacle to quickly and efficiently putting up housing.
This tension between development and tree preservation is at a tipping point in Seattle, where a new state law is requiring more housing density but not more trees.
One solution is to find ways to build density with trees. The Bryant Heights development in northeast Seattle is an example of this. It's an extra-large city block that features a mix of modern apartments, town houses, single-family homes and retail. Architects Ray and Mary Johnston worked with the developer to place 86 housing units where once there were four. They also saved trees.
"The first question is never, how can we get rid of that tree," explains Mary Johnston, "but how can we save that tree and build something unique around it." She points to a row of town homes nestled into two groves of mature trees that were in place before construction began in 2017. Some grow mere feet from the new buildings.
The Johnstons preserved more than 30 trees at Bryant Heights, from Douglas firs and cedars to oak trees and Japanese maples.
One of Ray Johnston's favorites is a deodar cedar that's more than 100 feet tall. The tree stands at the center of a group of apartment buildings. "It probably has a canopy that is close to over 40 feet in diameter," he notes.
This cedar cools the nearby buildings with the shade from its canopy. It filters carbon emissions and other pollution from the air and serves as a gathering point for residents. "So it's like another resident, really — it's like their neighbor," Mary Johnston says.
Preserving this tree required some extra negotiations with the city, according to the Johnstons. They had to prove their new construction would not harm it. They had to agree to use concrete that is porous for the walkways beneath the tree to allow water to seep down to the tree's roots.
The developer could have easily decided to take this tree out, along with another one nearby, to fit another row of town houses down the middle of the block. "But it never came to that because the developer was enlightened that way," Ray Johnston says.
Housing pushes trees out
Seattle, like many cities, is in the throes of a housing crunch, with pressure to add thousands of new homes every year and increase density. Single-family zoning is no longer allowed; instead, a minimum of four units per lot must now be allowed in all urban neighborhoods.
The City Council recently updated its tree protection ordinance, a law it first passed in 2001, to keep trees on private property from being cut down during development.
"Its baseline is protection of trees," says Megan Neuman, a land use policy and technical teams manager with Seattle's Department of Construction and Inspections. She says the new tree code includes "limited instances" where tree removal is allowed.
"That's really to try to help find that balance between housing and trees and growing our canopy," Neuman says. Despite the city's efforts to preserve and grow the urban canopy, the most recent assessment showed it shrank by a total of about half a percent from 2016 to 2021. That's equivalent to 255 acres — an area roughly the size of the city's popular Green Lake, or more than 192 regulation-size American football fields. Neighborhood residential zones and parks and natural areas saw the biggest losses, at 1.2% and 5.1% respectively.
Seattle says it's working on multiple fronts to reverse that trend. The city's Office of Sustainability and Environment says the city is planting more trees in parks, natural areas and public rights of way. A new requirement means the city also has to care for those trees with watering and mulching for the first five years after planting, to ensure they survive Seattle's increasingly hot and dry summers.
The city also says the 2023 update to its tree protection ordinance increases tree replacement requirements when trees are removed for development. It extends protection to more trees and requires, in most cases, that for every tree removed, three must be planted. The goal is to reach canopy coverage of 30% by 2037.
Developers generally support Seattle's latest tree protection ordinance because they say it's more predictable and flexible than previous versions of the law. Many of them helped shape the new policies as they face pressure to add about 120,000 homes over the next 20 years, based on growth management planning required by the state.
Cameron Willett, Seattle-based director of city homes at Intracorp, a Canadian real estate developer, sees the current code as a "common sense approach" that allows housing and trees to coexist. It allows builders to cut down more trees as needed, he says, but it also requires more replanting and allows them to build around trees when they can. "I definitely have projects I've done this year where I've taken out a tree that, under the old code, I would not have been able to do," Willett says. "But I've also had to replant both on- and off-site."
Willett recalls one development this year where he preserved a mature tree, which required proving that the site could be developed without damaging that tree. That also meant "additional administrative complexity and costs," he explains.
Still, Willett says it's worth it when it works.
"Trees make better communities," he says. "We all want to save the trees, but we also need to be able to get to our max density."
But Tree Action Seattle and other tree-protection groups frequently highlight new developments where they say too many trees are being taken out to make way for housing. This tension comes after a devastating heat dome hovered over the Pacific Northwest in the summer of 2021. "We saw hundreds of people die from that, hundreds of people who otherwise wouldn't have died if the temperatures hadn't gotten so high," says Joshua Morris, conservation director with the nonprofit Birds Connect Seattle. He served six years as a volunteer adviser and co-chair of the city's Urban Forestry Commission, which provides expertise on policies for conservation and management of trees and vegetation in Seattle.
"We know that in leafier neighborhoods, there is a significantly lower temperature than in lower-canopy neighborhoods, and sometimes it can be 10 degrees lower," Morris says.
Making space for trees
Seattle's South Park neighborhood is one of those hotter neighborhoods. Residents have roughly 12% to 15% tree canopy coverage there — about half as much as the citywide average. Studies show life expectancy rates here are 13 years shorter than in leafier parts of the city. That's in large part due to air pollution and contaminants from a nearby Superfund site.
In a cleared lot in South Park, 22 new units are going in where once four single-family homes stood. Three big evergreens and several smaller trees are expected to be cut down, says Morris. But with some "slight rearrangements to the configuration of buildings that are being proposed," Morris surmises, "an architect who has done an analysis of this site reckons that all of the trees that would be slated for removal could be retained. And more trees could be added."
Tree removals are allowed under Seattle's updated tree code. But removing larger trees now requires developers to plant replacements on-site or pay into a fund that the city plans to use to help reforest neighborhoods like South Park.
Groups such as Tree Action Seattle point out that these new trees will take many years to mature — sacrificing years of carbon mitigation work when compared with existing mature trees — at a critical time for curbing planet-warming emissions.
Morris says the trees that will likely be cut down for this development might not seem like a big number.
"This really is death by a million cuts."
He says trees have been cut down all over the city for years — thousands per year.
"At that scale, the cooling effect of the trees is diminished," says Morris, "and the increased risk of death from excessive heat is heightened."
Building codes aren't keeping up with climate change
Tree loss is not limited to Seattle. It's happening in dozens of cities across the country, from Portland, Ore., to Charleston, W.Va., and Nashville, Tenn., says Portland State University geography professor Vivek Shandas. "If we don't take swift and very direct action with conservation of trees, of existing canopy, we're going to see the entire canopy shrink," Shandas says.
He says current municipal codes don't adequately address the implications of climate change. The Pacific Northwest, Shandas says, should be preparing for increasingly hot summers and more intense rain in winter. Trees are needed to provide shade and absorb runoff.
"So that development going in — if it's lot edge to lot edge — we're going to see an amplification of urban heat," Shandas says. "We're going to see a greater amount of flooding in those neighborhoods."
Climate change is intensifying hurricanes and raising sea levels while also playing a role in wildfires. Such extreme conditions are outpacing building codes, explains Shandas, and he fears this will happen in the Northwest too.
Shandas says how developers respond to the building codes that Seattle adopts over the next 20 to 50 years will determine the extent to which trees will help people here adapt to the warming climate.
That matters in Seattle, where the nights aren't cooling off nearly as much as they used to and where average daytime highs are getting hotter every year.
A solution in the design
Architects Ray and Mary Johnston see part of the solution at another Seattle development they designed around an existing 40-year-old Scotch pine.
The Boulders development, near Seattle's Green Lake Park, transformed a single-family lot into a complex with nine town homes. The developer added mature trees he salvaged from other developments — transplanting them strategically to add texture and cooling to the landscaping.
Mary Johnston says building with trees in mind could also help people's pocketbooks. Boulders, she says, is an example. "Since these units have air conditioning, those costs are going to be lower because you have this kind of cooler environment," she says. Ray Johnston says places like this shady urban oasis should be incentivized in city codes, especially as climate change continues.
"Would you rather be living here with the shade we have ... or would you rather be in a much more urban, treeless, shadeless environment, where you can't hang out outside?" he asks.
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