Growing greener: U.S. cities are losing trees and their life-giving benefits. The scramble is on to replace them
Folks who think trees are just pretty don’t know how vital they are to survival. They’re a city’s hedge against pollution, flooding and heat islands, among others benefits.
EDITOR’S NOTE: We grow up. We grow old. We grow stronger and wiser. And sometimes we grow weary. In certain moments we grow closer. Other times we grow apart. How we thrive or falter depends on how we grow. At its roots is the idea of an abundant life for individuals, but also for communities and nations. Today, the Deseret News presents Part Two of Growing, an ongoing series.
SALT LAKE CITY — Two hundred trees don’t look like many, standing in a fenced enclosure, the majesty of the Wasatch Mountains behind them.
Not many, that is, unless you’re among the city’s urban forestry staff who unloaded them, wrestling a seemingly endless supply of 20-gallon containers from the semi-truck that carried them from the Oregon nursery that raised them.
At 7- to 10-feet tall each, they’re tricky for arborists who place them carefully on a Bobcat, then hurry alongside as they’re moved to the enclosure, to be lifted again and lined up by types.
Viewed across the city’s Public Services Department yard, it’s hard to sense the scale they’ll achieve when they’re planted around the city, where some may live 100 years and grow 60 feet tall.
Thinking that trees are just pretty is like reading a book jacket instead of the book. Those skinny trunks, resembling spindly legs of adolescent runners, may one day support a canopy that lowers temperatures warmed by city-hot asphalt, scrubs air, filters water, reduces flooding and shelters readers, strolling seniors and kids playing hide-n-seek. They may even slow mental decline.
Tony Gliot, Salt Lake City’s urban forester, expects all that and more. He’s part of a nationwide, purposeful push to replace trees that are disappearing from cityscapes coast to coast to the detriment of local inhabitants, wildlife and the environment.
American cities have a tree crisis.
Fading urban forest
In Japan, they refer to immersing oneself in nature as “forest bathing.” The health value is backed by 40 years of science showing humans need daily interaction with nature for well-being, said Sarah Hurteau, the Nature Conservancy’s director of urban conservation in New Mexico.
A 2016 study published in Environmental Health Perspectives divided 108,630 women in five groups based on how surrounded they were by trees and other greenery. They then looked at their health outcomes, controlling for socioeconomics, age, race, body mass, physical activity, smoking, education and other behavioral or health factors. The group surrounded by the most greenery had 12% lower mortality, 34% lower respiratory illness and 13% lower cancer death rates, compared to the group surrounded by the least amount of trees or other greenery.
Harvard’s Peter James, the study’s lead author, told The New York Times that the benefit came from four advantages the trees and other greenery provided: Less air pollution, more physical activity, more social engagement and better mental health.
U.S. Forest Service 2018 research says America’s 5.5 billion trees are worth roughly $18 billion a year in pollution removal and carbon sequestration, boosting energy efficiency by shading buildings and reducing vehicle emissions. Researchers credit trees with flood, noise and ultraviolet radiation reduction and herald the habitat trees create for wildlife — including pollinators.
That’s the good news. Here’s the bad: The nation’s canopy is shrinking.
Research in Urban Forestry & Urban Greening has found city tree populations declined in more than 40 states and Washington, D.C., a loss of 175,000 acres of trees nationwide. That’s hard to picture, but translates to 273 square miles of trees. The road from Chicago to Detroit is 283 miles. That’s a lot of trees. They’re felled by urban development, pests like the emerald ash borer, hurricanes and heavy snow, lack of care and old age, among other causes. At a time when city planners say they need more trees, cities would have to plant a combined 28.5 million trees annually just to keep up with what they’re losing.
The Forest Service researchers estimate at least $96 million in economic losses from steady tree decline over five years because lost trees don’t reduce air pollution, sequester carbon or reduce building energy use and power plant emissions.
Salt Lake’s trend is fairly typical. Gliot said it’s been losing trees for 20 years. The construction boon has ripped out many, while a huge number of the most common trees on public land, the Norway maple, have simply grown old, their lifespan spent. Ironically, some trees die because of how well people absorbed water-conservation messages. They save water and shortchange trees, “a competition between two precious resources. It just so happens the precious resource of a tree canopy requires water in order to thrive. I think the return we get from an urban forest is worth that expenditure, provided we are watering correctly and responsibly. We can do that and still conserve water,” he said.
Fear kills trees, too, said Amy May, executive director of Tree Utah. People get scared older trees will drop limbs on structures — it sometimes happens — and cut a tree’s life short.
Urban forest dilemma
The Nature Conservancy’s Planting Healthy Air report looked at air quality in 245 big cities around the world and concluded spending $4 on planting trees per resident in each city would improve health for millions. The impact, though, is felt where the trees grow, so they have to be planted widely and wisely.
The Nature Conservancy said trees are especially important in cities, where temperatures trend higher because of heat islands, which happen when concrete, building roofs and other impervious surfaces absorb heat during the day and radiate it back out at night, so temperatures are hotter in the city than nearby. Trees can help cool that down, but they can also get into a too-hot cycle that short-circuits them. Heat stress hurts trees as well as people.
The Environmental Protection Agency says roofs and pavement can be 50 to 90 degrees F hotter than the air on a sunny day. City air temperatures after sunset can be 22 degrees warmer than air in surrounding areas.
Heat waves are one possible result, May said, leading to health consequences like asthma, heart attacks and heat exhaustion. People even die. But studies say evaporation from a single tree can produce the cooling effect of 10 room-size air conditioners operating around the clock.
The report calls street trees “part of a cost-effective portfolio of interventions aimed at controlling particulate matter pollution and mitigating high temperatures in cities. While trees cannot and should not replace other strategies to make air healthier, trees can be used in conjunction with these other strategies to help clean and cool the air.”
Nature in cities has been largely an afterthought, said Hurteau. Often, trees were ripped out to build a city. Now including them is very much on the mind of urban planners. For instance:
- Louisville, Kentucky, is one city where trouble is cooking. The Georgia Institute of Technology said Louisville’s heating faster than other metro areas in part because it loses more than 50,000 trees a year. The National Institutes of Health and The Nature Conservancy are funding an experiment to plant large trees as part of its Green Heart Project, which will track 700 people, half living by those new trees and half not to see their health the next five years.
“Design cities and neighborhoods that first think about health, not last,” study leader Aruni Bhatnagar of the University of Louisville, told NPR. “That should be the first consideration before you put a single brick into a neighborhood.”
- Seattle is boosting tree stock and pondering more equitable socioeconomic distribution. Trees for Seattle, the urban forestry effort, is tracking progress toward reaching canopy goals for 2037 that were set in 2007. The goal is 30% of Seattle “under canopy,” meaning what would be covered by trees if one flew overhead. They’ve exceeded goals in places like industrial areas and developed parks; they’re close to reaching goals downtown, in commercial and mixed-use areas and in residential neighborhoods.
- Urban green space gets attention from health experts, urban planners and others, even politicians. Both candidates for Salt Lake City mayor, for example, talked about the importance of environmentally healthy, green communities. Erin Mendenhall promised to plant more trees on the west side, while Luz Escamilla said that “there’s a lot more we can and should do in terms of cleaning our air, protecting our environment, and promoting our open spaces.”
- Gliot’s department plants trees in parking strips at residents’ requests. Tree Utah and partners plant thousands of trees a year, many in public parks and school yards where a tree may become part of a science lesson, May said. Both settings require bigger, more expensive trees. They also plant along river corridors and other places trees have been disturbed.
- Hurteau works with 24 urban conservation colleagues across the country. Science guides their efforts. She works especially closely with those concerned, like New Mexico, about heat island issues. Their goals are similar, but the ecological reality of each city can be quite different, she said.
Not enough variety
While some folks were razing trees to build cities, places like Albuquerque added trees in what was grassland, hungry for canopy. Officials gave away Siberian elm seedlings around the 1920s and for close to a century those trees provided incredible shade. Now they’ve reached old age.
No one planned for that until recently. “Young trees take a long time to grow,” said Hurteau, who notes lots of trees in urban environments only make it a decade — bad news as it takes eight to 10 years to reap ecosystem benefits like carbon sequestration or air and water filtering that pay back the investment.
“We are planting like crazy, trying to get as many trees into the ground as we can to get a head start in the gap I imagine is coming in our existing canopy,” she said.
That so many trees are the same age is always problematic for cities, said May.
“The right tree in the right place” has become a tree planter’s mantra. Trees face lots of physical competition: overhead power lines, underground utilities, roadway sight lines, ADA accessibility and physical space requirements. A tree planted too close to a house may need to be cut down 20 years into its 80-year expected life. Another might be sacrificed because its root system was wrong for its parking strip location, tearing up sidewalk.
Hurteau said tree experts in her state recently evaluated 130 tree species against future projections that include predicted temperatures, urban population growth and heat island issues. They’re looking for trees that can survive whatever the weather’s expected to throw their way.
Some conservation efforts have gotten snagged in debate over climate change. You don’t have to be convinced of that to root for trees. Hurteau said self-interest alone could provide reasons for trees, from health to the fact that outdoor tree-lined shopping districts convince people to spend 12% more, boosting local economies.