Climate change is making it harder to predict when or if Maine’s fall foliage will reach its colorful zenith.

The annual color reveal begins when the shorter days and colder temperatures of autumn prompt trees to prepare for winter. Leaves stop making the green chlorophyll needed to turn sunshine into nutrients, clearing the way for the underlying yellow, gold and red pigments to emerge.

Warmer fall temperatures, especially at night, mean leaves are making chlorophyll longer, pushing peak color back, on average, nine days later in October compared with the 1950s, according to research cited by the Maine Climate Council. Under some scenarios, Maine foliage could peak in November by 2060.

While warmer temperatures may delay peak foliage, other aspects of climate change – wild precipitation patterns pinballing between drought and deluge, high winds from extreme weather, and more tree blight and pests – could dull, discolor or drop the autumn leaves before they reach peak color.

“The rules of the game seem to be changing and the knowledge we took for granted does not necessarily apply to what’s happening now,” said Aaron Bergdahl, a forest pathologist with the Maine Forest Service. “The only thing we know for certain is that fall is becoming much more unpredictable.”

That volatility makes it difficult for scientists to predict the knock-on effect on Maine’s tourism industry, which raked in nearly a half-billion dollars last fall, and the health of Maine forestland, which supports a profitable paper industry, provides food and shelter for wildlife and absorbs harmful greenhouse gases.

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There’s still a lot to learn about our changing fall, scientists say, and a lot riding on getting it right.

Trees changing colors line a cove on Little Ossipee Lake in Waterboro. Shawn Patrick Ouellette/Staff Photographer

Here’s what we do know: A review of the satellite data and archival records reveals peak foliage at Acadia National Park is now happening nine days later than it was in the 1950s, according to Stephanie Spera, an assistant geography professor at the University of Richmond in Virginia.

According to Spera, satellite data shows Acadia’s peak foliage now happens in the third week in October, or Oct. 14 or 15. That is nine to 10 days later than peak foliage dates recorded in newspaper stories and park visitor photographs of the 1950s, Spera said.

Spera found a strong correlation between a warmer fall and the delayed arrival of peak foliage at Acadia, a trend that she said is likely to apply across Maine even though peak foliage occurs at different times in different regions. Just like all of Maine is getting warmer, all of Maine is seeing fall colors arriving later.

Last year, Maine saw its fourth-warmest fall – 48 degrees, or 4.2 degrees above the historical average – since it began keeping records in 1895. The impact of climate change was even more pronounced at night, with the average minimum temperature of 39.1 degrees tying for the warmest on record.

Fall foliage on display at Riverside Memorial Cemetery in Cape Elizabeth. Derek Davis/Staff Photographer

Acadia has warmed by 3.4 degrees over the last century, a change being felt by trees, plants and wildlife throughout the park  One out of five plant species documented in the park a century ago are gone. Seven of the park’s 10 most common tree species are expected to decline or possibly even disappear by 2100.

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Spera’s research found Acadia’s Septembers, Octobers and Novembers to be warmer, especially at night, and wetter than in 1950: Average daily temperatures are 2 degrees warmer, nightly lows are 2.24 degrees warmer and rainfall is increased by 2 inches.

But a closer look at Spera’s data reminds us that temperature is not the only driver of fall foliage timing or brilliance. Otherwise, the rate of foliage delay would have accelerated in tandem with warming rates. Instead, Maine’s foliage is peaking about the same time it did in 2000. Why?

That’s because other foliage variables, like drought, storms and pestilence, have more opportunity to disrupt or even derail peak foliage the later it happens. Drought can cause dullness and early leaf drop. Heavy rains breed fungal infections that can discolor leaves. Storms can denude the trees altogether.

Spera laughs as she recounts learning this lesson the hard way while conducting her research in Maine.

Foliage is just beginning to show around Sokokis Lake in Limerick on Oct. 9. Shawn Patrick Ouellette/Staff Photographer

“When I was doing my work at Acadia, we were well on our way to a gorgeous fall season, all the pieces in place for brilliant color, when a storm swept in and stripped every yellow, orange and red possibility right off the trees,” Spera said. “So much potential … lost. I was heartbroken.”

Climate change is increasing the likelihood of all these potential spoilers – Maine’s future climate is expected to see more precipitation extremes, often including drought and deluges within the same year, according to the Maine Climate Council.

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Increased precipitation causes fungal infections that can weaken trees and mar their colors if they turn, according to Bergdahl, the tree pathologist. The number and variety of invasive species will increase as winters become milder, making trees more susceptible to blight and early leaf drop.

Last year’s foliage season was marred by a high incidence of leaf disease that caused blemishes, an early crown thinning and an early leaf drop, Bergdahl said. Conditions looked perfect for fall foliage this year until about a month ago, he said. Increasingly dry conditions are likely to mute the bright colors.

Colorful fall leaves begin to cover a truck sitting at the edge of the woods in a backyard in Sanford on Oct. 10. Brianna Soukup/Staff Photographer

“All of these little nuances have impacts that we’re still trying to understand,” Bergdahl said.

For example, Maine’s future climate is likely to be wetter, Bergdahl said. Will that lead to an increase in beech leaf disease? If so, what happens to the black bear, who loves to eat beech nuts? Will sows birth fewer cubs? If so, Maine’s population of 35,000 black bears – the largest in the lower 48 states – will fall.

While a longer growing season does increase the carbon uptake of a forest, a delayed fall probably won’t increase the storage capacity of a forest in the same way that the earlier arrival of spring will, according to Daniel Hayes, an associate professor at the University of Maine School of Forest Resources.

“Trees are gangbusters for photosynthesizing in the spring – so that makes a big difference,” said Hayes, who studies biomass and carbon inventory. “They’re already pretty well wound down by October anyway so a few more days doesn’t really get us much.”

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Maine’s forests absorb 22.2 million tons of greenhouse gases from the atmosphere. According to its last carbon report, Maine has achieved 91% of its 2045 neutrality goal by cutting greenhouse gas emissions, using less fossil fuel and increasing carbon storage, especially in its forests.

A couple of stops to take pictures on a trail through the Eastern Promenade on October 2. Derek Davis/Staff Photographer

A changing climate poses challenges at Acadia: stressing the power grid and cooling systems, damaging roadways, requiring shade and cooling structures to shield visitors from the summer heat, finding staff to work an extended foliage season, and the early October closure of the Island Explorer shuttle service.

Maine’s tourism industry makes about $1 billion in the shoulder season but, like Acadia, it struggles to find seasonal workers to staff the hotels, restaurants and parks catering to leaf peepers. But it’s a good problem to have, according to Tony Cameron, chief executive office of the Maine Tourism Association.

Fall tourism in September and October now accounts for 20% to 25% of annual industry profits, he said. He doesn’t yet have the receipts from last month, but from what he’s heard, the industry did better this September than it did a year ago. Last month’s glorious weather certainly didn’t hurt, Cameron said.

Both the peepers who take Maine vacations and those who shelter, feed and entertain them upon their arrival would love to be able to predict peak foliage with certainty, Cameron said. But it’s not necessary, he said. People want to see the color, but find plenty of things to do once they get here.

“If they miss it, it just gives them a reason to come back next year,” Cameron said. “And the year after.”

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