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Updated: September 19, 2023

Leaf-peeping season may be shifting at Acadia, and extending fall tourism

colorful trees from hilltop Courtesy / Schoodic Institute A new study shows that climate change might be shifting the leaf-peeping season later into the fall — which could inform trends in demand for visitor services in Acadia.

Leaf-peeping season has long been a popular time to visit Acadia National Park, and it could become even more popular.

In recent years, warming temperatures and climate change may have extended the fall tourist season, with more people now visiting the park in September and October, according to a new study led by second Century Stewardship Fellow Stephanie Spera of the University of Richmond and published recently in the journal Landscape Ecology.

For the park, the changes mean growing demand for visitor services into the spring and fall.

“Not only are we seeing visitation numbers increase, we are also watching the peak visitation season get longer,” said Acadia Superintendent Kevin Schneider.

The study is based on National Park Service records, newspaper archives, historical photographs contributed by hundreds of Acadia visitors, and satellite data.

On average, peak fall foliage is now occurring almost two weeks later than it did in 1950.

“If we only looked at the satellite data since 2000, we would not have found any trend,” said Spera. “It was because of the archival, citizen science that we were able to extend the data set and detect the longer-term trend.”

Spera said she connected with people like Bill Skocpol, who has a cabin on Little Echo Lake, and took photographs every October for 30 years. 

‘Brownness index’

Leaf-peeping is a billion-dollar industry in New England, as visitors travel to view red and orange maple trees, gold birches and yellowing marsh grass. 

Over the past 20 years, September and October have had the greatest increases in visitors to Acadia. 

Spera said a goal was to determine to what extent visitors are traveling at that time for foliage or the weather.

“One of the goals of the National Park Service is to provide for high-quality recreation experiences,” said Adam Gibson, a social scientist with Acadia. “Understanding the motivations and expectations of visitors helps us do that.”

The study hinged on the question of whether the leaves are turning colors later in the year

Temperature and precipitation have been correlated with the length and vibrancy of fall color. Some studies show that a hot summer, rainy fall and even nitrogen pollution are related to a shorter, duller foliage season, while a later color change is associated with warmer, earlier spring and fewer fall storms. 

Spera tested these relationships by tracking when the leaves begin to change using a “brownness index” based on satellite data and photography, and analyzing rain and temperature measurements from stations in Acadia and across the Northeast. She also established fixed photo stations at several locations within Acadia where volunteers could take pictures to help validate satellite data.

When does the ‘peak’ peak?

The data analysis was challenged by the lack of a universal definition for when the “peak” of peak fall foliage occurs, since leaves change color over days and weeks, making it something of an inexact science.

“We included all records that used the word peak, and used the average when there was a range of dates,” said Spera.

But climate data showed significant increases since 1950 on Mount Desert Island across multiple criteria: minimum temperatures, maximum temperatures, precipitation, and the numbers of warm days and nights, hot days and nights, and downpour days.

Warmer temperatures in particular consistently correlated with delayed timing of peak fall foliage. Air temperature and decreasing daylight provide cues for trees to begin shutting down chlorophyll production, which makes other pigments in leaves visible. 

“September temperatures seem to be the most important variable in predicting the timing of peak fall foliage, with warmer Septembers resulting in later peak fall foliage,” said Spera.

In general, she said, peak foliage is occurring later, shifting from early to late October. Later peak color also was associated with more rain in May. 

The links between climate and color also vary by species; some trees are more tolerant of drought than others, said Spera.

Second Century Stewardship is a partnership of the National Park Service, National Park Foundation, David Evans Shaw Family Foundation and Schoodic Institute at Acadia National Park.

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