In a state where foliage-related tourism is an economic driver, there's hope that each fall will bring vibrant colors. But, like so many other aspects of the state’s natural landscape, climate change is affecting fall leaves.
Tree scientists don’t have a crystal ball on exactly how foliage will turn out, but they can make some educated guesses based on previous weather, trees’ overall health and expected fall weather.
This fall's outlook isn't looking too promising after a cool wet spring, and a dry, hot summer. Now, most of the state is in a drought, with some of the worst conditions in the north.
But “fall foliage is extremely complex,” said Steven Roberge, a forester with the UNH Cooperative Extension.
Roberge said heavy rain can lead to dark spots and leaf dimpling and dry conditions can hurt trees further. Still, he said what matters more is the weather during the fall itself. He said ideal foliage conditions are like ideal maple sugar conditions: cold nights and bright, sunny days. The larger concern is if those temperatures don’t happen, he said, not just the weather so far this year.
“We may just have more of a muted kind of response if we don't have those colder temperatures during the fall,” he said.
But other scientists, like Nat Cleavitt at Hubbard Brook Experimental Forest in Woodstock, think the damage may already be done.
She’s pessimistic that this extreme “zigzagging” left trees “stressed out.”
“The leaves are only getting worse,” said Cleavitt. “I would think that we're going toward more browns and yellows and not toward a lot of vivid colors.”
She said the rainy spring led to insect damage, which she saw in the sugar maple, American beech and yellow birch she’s studying at Hubbard Brook. All of those species had thrip and young caterpillar damage.
Then, she said the summer weather became hot, dry and sunny, which sucked water out of the trees’ leaves and led to canopy dieback.
Amey Bailey, a forest technician also at Hubbard Brook, echoed Cleavitt’s observations. She said the drought has caused early deterioration in certain species, leading to some brown leaves already cropping up. She described this year as “a perfect storm” of challenges for trees.
“They're just kind of giving up,” she said.
Different species are more resilient to drought than others. Beech trees, which make up about 30% of hardwoods in the state, are particularly vulnerable. Cleavitt predicts large swaths of them will die this year, like they did following the 2021 drought.
Trees play a crucial role in fighting climate change by removing carbon from the atmosphere, but when trees are under stress they can’t function as well.
“An unhealthy forest is not capturing as much carbon as a healthy forest for sure,” she said.
Climate change is making these extreme weather swings more common. In New Hampshire, climatologists predict the state will become wetter and warmer and more at risk for short-term droughts. Bailey said warming temperatures will likely change fall in complicated ways.
“Climate change is causing it to stay warmer later into the fall, and so the trees have the potential to keep green on longer because it's warm,” she said. “But climate change has caused so much stress to the trees that they really can't flourish the way you might wish them to.”
Peak foliage varies across the state, ranging from late September in the North Country to late October in the southern part of the state.
Roberge, the forester with UNH extension, wants people to spend some time in the woods this fall regardless of what predictions people like him have made.
“Get out there, experience the landscape, because you're definitely going to find either one brilliant tree that the sun hits just right or a vista that looks great,” he said.
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