As the driest summer in Seattle’s record books comes to an end, trees across the city are sounding a silent alarm.
It was the latest in a string of Seattle summers over the past decade, including a record-breaking heat dome in 2021, accompanied by drought conditions and warm temperatures that have led to prematurely brown leaves and needles, bald branches and excessive shedding. Have left several trees with seeds – all signs of stress.
You see it in big-leaf maples and hemlocks, just full of cones or seeds, it’s their last-ditch effort to breed, said Shea Cope, an arborist at the Washington Park Arboretum, which covers 230 acres (93 acres). hectare) is spread in the north. of city.
That heat was fatal for three important trees in the park’s pine collection, including an 85-year-old Japanese red pine infected with a fungus left behind by the beetles.
We’re losing our broad-leaf, deciduous conifers faster than they do, said Cope as he surveyed a giant knobcone pine that had half its canopy dead.
Cities around the world have pledged to plant more carbon-absorbing trees to help fight climate change. Research has shown that the shade of mature trees also helps reduce unhealthy heat islands, especially in poorer areas.
President Joe Biden’s Inflation Reduction Act pumped $1.5 billion into the Forest Service’s Urban Tree Program money to get cities to plant and maintain even more.
Climate Threats to Urban Forests
Life in a city can be especially difficult for a tree, and those challenges are increasing with global warming.
Researchers from France and Australia analyzed the impact of warmer temperatures and less rainfall on more than 3,100 tree and shrub species in 164 cities in 78 countries. They found that about half the trees were already exposed to climatic conditions beyond their range. They also concluded that by 2050 almost all trees planted in Australian cities will not survive in urban areas.
If trends continue, we’re going to see a lot of trees die,” said Nicholas Johnson, an arborist with Seattle City Parks. Trees become weak in summer like humans.
Johnson said heat and drought force trees to expend living energy that would otherwise go to regeneration, growth or fighting disease and pests. Everything out there is trying to eat a tree. The tension escalates.
Human-caused climate change also promotes more extreme weather such as strong wind, rain and freezing temperatures.
David Novak, a retired US scientist, said it’s not the gradual change that’s going to be the problem, it’s too much water, too little water, too much wind and these extreme changes in storm intensity that are causing these extremes. are causing the changes. Forest Service.
Hurricane Katrina wiped out about 10 percent of the trees in New Orleans in 2005, said Michael Karam, director of parks and parkways. And in 2021, he said, Hurricane Ida uprooted many new plants.
He said that the need to increase the canopy is more than in previous years. But in urban settings the advantage remains the same. On any hot day, step into the shade and you’re reminded of what a benefit trees are to public health and well-being.
A 2018 study by Novak found that 25 states saw significant tree declines at the beginning of that decade.
Housing and commercial construction, compacted soil, pollution and even car accidents all contribute to the loss of the city’s canopy.
Cities are familiar with large-scale tree damage, but usually one type of tree is affected, such as birches killed by borer insects.
With climate change, researchers worry that canopy loss will exceed the rate at which newly planted trees reach maturity, which takes 10 to 20 years.
You have an increasing rate of tree mortality coming to a city near you, said Aaron Ramirez, a tree researcher at Reed College.