Maine is known for its vivid displays of autumn color, but climate change is making it harder for scientists to predict when foliage season will start or how long it will last.
Fall days and nights are getting warmer which is changing when trees stop producing chlorophyll to get ready for the winter, said Aaron Bergdahl, a forest pathologist with the Maine Forest Service.
That process allows yellow, red and orange pigments to come through in leaves that eventually drop off.
"If those two things happen very closely together because of longer, warmer autumns, then that can potentially impact what we see in terms of fall foliage," Bergdahl said.
Increasingly unpredictable weather can affect foliage too. Lots of rain or a drought during the growing season can impact tree health, according to Bergdahl. A wet spring and summer, for example, can increase the chance of fungal diseases and cause premature defoliation, he added.
Warmer fall weather might even disrupt the foliage process to the point that leaves may drop before fully developing colors, Bergdahl said.
"These are questions that we just don’t know the answer to, because the rules of the game have changed. What we thought we knew about fall foliage is really up in the air right now," Bergdahl said. "The seasons are a little bit different and our growing seasons are less predictable and generally have a little bit more stress than what we recognized 10, 20, years ago."
Research from Acadia National Park found peak foliage season now arrives more than a week later than it did in the 1950s. And by 2060, that period could shift to late October and early November.
The study, published last year in the journal Landscape Ecology, concluded that "minimum temperatures, maximum temperatures, precipitation, and the number of warm nights, hot nights, warm days, hot days, and downpour days have all significantly increased," affecting the timing of foliage.
There's no comparable records for other parts of Maine, but Bergdahl said the Acadia example could be applied to the rest of the state.
Even with all the uncertainly brought on by a warming planet, Bergdahl is optimistic locals and visitors alike will get to enjoy foliage season well into the future.
"Despite the challenges posed by climate, I believe that when it’s fall in Maine, you can always find beautiful fall foliage somewhere due to the diversity of our landscapes and our overall healthy forests," he said.
Maine Public’s Climate Desk is made possible by Androscoggin bank, with additional support from Evergreen Home Performance, Bigelow Laboratory, & Lee Auto Malls.
