The driest summer in Seattle’s history ended and trees all over the city were sounding their alarms.
This was the latest in a series of Seattle summers over the past decade. It featured drier conditions with higher temperatures and more severe weather that left many trees with prematurely brown leaves and needles, balding branches, and excessive seeding — all signs and symptoms of stress.
“You can see it in big-leaf maples and hemlocks just loaded with seeds or cones, it’s their last-ditch attempt to reproduce,” stated Shea Cope, an Arborist at Washington Park Arboretum (a sprawling park covering 230 acres (93 ha) north of downtown).
Three “significant” trees of the park’s pine collection were killed by fungus this summer, including an 85-year old Japanese red pine that was infected by beetles.
Cope said, “We’re losing conifers quicker than our broad leaf deciduous ones,” as he observed a knobcone pine tower with half of its canopy gone.
To combat climate change, cities around the world have committed to planting more carbon-absorbing trees . Research shows that shade from mature trees can help reduce heat islands, especially in poor areas. President Joe Biden’s Inflation Reduction Act infused $1.5 billion to the Forest Service’s Urban Tree Program — money that cities can use for more planting and maintenance.
Urban Forests and Climate Change
Trees can find it difficult to live in cities, and these challenges are increasing with global warming.
Researchers from Australia and France studied the effects of warmer temperatures and less rainfall on over 3,100 tree species and shrub species. They did this in 164 cities across 78 nations. About half of the trees were already experiencing extreme climate conditions. The researchers concluded that almost all Australian tree species will be unfit to survive in urban environments by 2050.
Nicholas Johnson, an Arborist for Seattle City Parks, stated that “if trends hold, there will be a lot more trees die.” “Under heat, trees get weak — just like people.”
Johnson stated that heat and drought make trees spend energy to survive, which would otherwise be used to regenerate, grow, or fight off disease and pests. Johnson said, “Everything outside is trying eat a tree.” These stresses are multiplied.
Climate change caused by humans also causes extreme weather like intense wind, rain, and freezing temperatures.
“It’s not gradual change that’s going be the problem. It’s these extreme swings in too much water, to little water and storm intensities that are going to cause these rapid changing,” stated David Nowak, a former scientist with the U.S. Forest Service.
Michael Karam, Director Parks and Parkways, stated that Hurricane Katrina destroyed about 10% of New Orleans’ trees during 2005. He also said that Hurricane Ida in 2021 will have many new saplings.
He stated that “the need to expand the canopy is greater today than it was in years past.” The benefits of urban environments are the same. You’ll be reminded of the benefits of trees on hot days by going in the shade.
Nowak’s 2018 study found that 25 states experienced significant tree declines in the previous decade.
A city’s canopy is affected by factors such as housing and commercial construction, pollution, and even car accidents.
Large-scale tree loss is a common problem in cities, although it usually affects one type of tree, such as birches that have been attacked by a pest. Researchers are worried that the rate at which new trees reach maturity will be affected by climate change. This usually takes between 10 and 20 years.
Aaron Ramirez, a Reed College tree researcher, said that “a rising rate of tree mortality is coming to a town near you.”
According to a report by the city, Seattle saw a 1.7% reduction in its tree canopy between 2016 and 2021. This is approximately 255 acres (255 ha) of trees. Portland, Oregon saw its first decrease in canopy last year since it started keeping records over two decades ago.
We’ve spent a lot time discussing the health of our forest in rural areas, as we’ve experienced increased stress from diseases, insect infestations, drought — which has led to devastating wildfires. Hillary Franz, Washington State Commissioner for Public Lands, stated that our urban forests, and our urban tree are equally stressed.
At a Bellevue maintenance lot, rows of black plastic pots soak in the morning sun. Each pot is home to juvenile giant sequoias that are just a few inches high. The city is trying to increase climate resilience by growing them all.
Sequoias don’t grow in the Pacific Northwest. However, tree managers in Seattle are increasing their use of them to combat pests and drought.
Rick Bailey, the supervisor of the city’s forest management program, said, “Once these trees have been established, they grow incredibly quickly.” About 70% of all new trees are still planted in native trees.
For a long time, non-native trees were brought into cities. Many arborists are now recommending that they include non-native trees in their city’s tree list due to climate change. This is called “assisted migrating.”
Scott Altenhoff, Oregon’s Urban and Community Forest Program, stated that arborists are searching for non-native species with no “invasive tendencies”.
Ramirez, Reed College, stated that there is still much to be learned about resilient trees. His lab discovered that the Alaska cedar performed better than California and Oregon varieties in hot summers.
The planting of more non-native trees will increase the value of what city arborists have learned over decades from tree deaths: that diversity in the types of trees planted is crucial to maintaining urban forests.
The small Puget Sound town of Burien in Washington,, which has around 80 employees, hired a second tree manager in March. This hiring was part of a greater focus on the city’s canopy.
“We had a conversation about ‘Can you get a watertruck? Josh Petter, the new Arborist, said something similar. “Because we do have these increasing dry periods… I’d rather plant 1 tree and keep it really well than 10 trees that aren’t maintained.”
Budgets are affected by the costs of maintaining urban forests. New Orleans is considering a new water truck after the dry year. Bellevue is home to giant sequoias. A large portion of tree maintenance funds go toward removing dead trees.
Evan Mallen, Georgia Tech, said that “we are not keeping up the level of maintenance and protection necessary to ensure they’re not losing them.” He also said that more cities will need legislation to protect existing trees.
Volunteers from the Seattle parks department planted many trees in a park west to the city during a recent rainy weekend. One of them was a western red Cedar planted in the shadows of fallen oak roots.
Johnson, the department’s Arborist, stated that “Life always finds its way.” “And people in Seattle are helping life find its way.”