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PORTLAND, Maine – Droughts that cause leaves to turn brown and wilt before they reach full color. Heat waves causing leaves to fall even before autumn arrives. Extreme weather events like hurricanes which completely strip trees of their leaves.
For a cheerful fall activity, leaf viewing faces serious threats from the age of climate change.
Leaf watching, the practice of traveling to watch nature display its fall colors, is a beloved annual activity in many parts of the country, particularly in New England and New York. But recent seasons have been disrupted by weather conditions there and elsewhere, and the trend is expected to continue as the planet warms, arborists, conservationists and environmentalists have said.
Typically, at the end of September, the leaves cascade in warmer hues across the United States. This year, many regions have not even left their summer green hues yet. In northern Maine, where peak conditions typically arrive in late September, rangers reported less than 70% color change and moderate leaf drop on Wednesday.
Across the country in Denver, high temperatures have left “Dead and dry leaf edges” early in the season, said Michael Sundberg, a certified arborist in the area.
“Instead of trees making this incremental change, they experience these wacky weather events. They change all of a sudden, or they drop the leaves early ”, Sundberg said. “It’s been a few years since we had a really good leaf year where you just drive around town and see some really good colors.”
The reason why climate change can be bad for fall foliage has a little to do with plant biology. When fall arrives and the length of the day and the temperature decrease, the chlorophyll in a leaf breaks down, causing it to lose its green color. Green gives way to yellows, reds and oranges which create spectacular fall displays.
Achieving these peak colors is a delicate balance and compromised by changes in the environment, said Paul Schaberg, research plant physiologist at the US Forest Service based in Burlington, Vermont. Warm fall temperatures can cause leaves to stay green for longer and delay the onset of what peepers are looking for in terms of fall color, he said.
Worse, dry summers can stress trees and cause their leaves to completely lack fall color, Schaberg said. A 2003 study in the journal Tree Physiology that Schaberg co-authored stated that “Environmental stress can accelerate” leaf deterioration.
“If climate change means severe drought, it means trees will close and many trees will just lose their leaves. “ he said. “Severe droughts which really mean the tree just can’t function – it doesn’t improve the color.”
It’s already happening. This summer’s heatwave in the Pacific Northwest brought temperatures over 110 degrees Fahrenheit (43 Celsius) to Oregon, leading to a condition called “Leaf burn”, in which the leaves turned brown prematurely, said Chris Still, a professor in the Forest Ecosystems & Society department at Oregon State University.
The pigment in the leaves degraded and they fell off shortly after, Still said. This will result in a less scenic fall season in parts of Oregon.
“This is a very good example of a change in color solely due to the shock of the heatwave” Always said.
Climate change also poses longer-term threats that could disrupt the viewing of the leaves. The spread of invasive diseases and pests and the northward shift in tree species are all factors related to warming temperatures that could make fall colors less vivid, said Andrew Richardson, professor of ecosystem science at Northern Arizona University.
The onset of fall colors, which drifted later into the fall, could also continue to arrive later, said Jim Salge, foliage expert for Yankee magazine.
“My observations over the past decade have had more years that were later than what we would consider historical averages,” he said.
The economic impact of poor leaf viewing seasons could also have consequences. Officials across New England have said fall tourism brings billions of dollars to these states every year.
Environmentalists say this is a good reason to focus on preserving forests and reducing the burning of fossil fuels. Recent fall seasons have been less spectacular than usual in Massachusetts, but leaf viewing can remain a part of the state’s heritage if forests are given the protections they need, Andy Finton said, director of landscape conservation and forest ecologist for The Nature Conservancy.
“If we can keep the great and important forests intact, they will provide what we have depended on: clean air, clean water, clean forests, and the inspiration of autumn.” said Finton.
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