Following a dry summer, plant scientists are predicting the leaves will change color later this year, with many still counting on a colorful fall.
The state Department of Conservation and Recreation’s Interactive Fall Foliage Map predicts the fall colors will peak between Oct. 27 and Nov. 3. According to the Old Farmer’s Almanac, this lands a week later than the typical peak for New England’s brightest colors — the second and third weeks of October.
To understand this year’s foliage forecast, local experts broke down the science behind the changing leaves.
According to Tony Reiber, who teaches horticulture and runs the Farm and Food Systems program at Greenfield Community College, trees sense the days shortening in the fall. With less sunlight, the plant cells stop creating chlorophyll, the chemical that absorbs sunlight during photosynthesis and gives the leaves their green hue in the spring and summer.
“As the days get shorter, the chlorophyll will start to break down, because it requires a lot of energy for the plants to make chlorophyll,” Reiber explained.
Without chlorophyll, the leaves blush into the colors of the chemicals underneath chlorophyll, often the yellows and oranges of carotenoids. In other words, leaves do not create these colors; they become the color of these chemicals already in their makeup.
“They’re always there, they’re just not visible because the chlorophyll is a dominant pigment,” Reiber said.
As for reds, the leaves produce anthocyanin from stored sugars. Reiber said the carotenoids and anthocyanins act as a sunscreen for the leaves, protecting the plant cells.
Elsbeth Walker, a plant biology professor at the University of Massachusetts Amherst, compared the protective yellows, oranges and reds to a summer tan.
“The darker pigments in your skin are protective,” Walker explained. “Imagine if you sat outside and you didn’t have any clothes on and you didn’t have any sunscreen on. Think how sunburnt and hurt by the sun you’d be, and that’s what trees are doing every day.”
Cooler temperatures also tell the trees to shed their leaves. Ashley Keiser, an assistant professor of soil and ecosystem ecology at UMass Amherst, explained that the trees must sense a significant gap between daytime and nighttime temperatures. ClimateCentral.org declared a drop of 9 to 12 degrees as the sweet spot.
“Those cooler nights that we had that really felt like fall, it’s a great signal for the trees,” Keiser explained.
“Trees love getting down in the low 40s, mid to high 30s,” said Richard Harper, who teaches urban and community forestry at UMass Amherst.
With the chilly September nights, one scientist expects an even brighter fall this year.
“I expect to have a full spectrum of colors,” said Peter Jeranyama, who teaches plant physiology at UMass Amherst.
Harper and Walker also predict that the region’s dry summer may cause the trees to shed their leaves later in the season to conserve water. The Executive Office of Energy and Environmental Affairs declared a Level 2 Significant Drought in the Connecticut River Valley on Sept. 9.
Keiser said dry soil can dull the vibrancy of foliage. According to the U.S. Department of Agriculture, a warm patch of weather can also dim fall colors.
Keiser samples soil in Harvard Forest in Petersham for her research lab at UMass. In recent samples, Keiser noticed low moisture levels in the soil. She hopes more rainfall will help nourish the dry soil, brighten the leaves and even possibly prolong the foliage season.
“I think it’s a mixed bag. We’re not as dry as we were last year, so that’s promising, but it’s really hard to tell,” Keiser said. “But maybe the damage is done from the summer. I guess we’ll see.”
Each scientist stressed that forecasting foliage is difficult, due to multiple factors like sunlight, temperature and rainfall.
“Even if this year’s not going to be the perfect foliage season, I still say, it’s still New England,” Harper said. “People are still going to travel all over the world to come to New England to see the autumn leaves change, so fear not.”
Harper traced New England’s classic fall colors to its “rare combination” of cool nights and bright native trees. Chilly late summer and fall nights awaken the crimsons of red maple trees and scarlet oaks, and the oranges of sugar maple trees and American beech trees in Massachusetts’ forests.
“Even poison ivy turns red this time of year,” Harper noted.
Before moving to Pelham, Keiser’s experiences with autumn in Colorado were one-note.
“You get this one whole sea of yellow with the aspens, but you just don’t get the pops of orange and deep red and some of that purply color,” Keiser recalled. “We get this rainbow and vibrancy in New England foliage I just think is so striking.”
Plant scientists’ favorite foliage spots
Outside of their classrooms and labs, local experts enjoy watching the leaves change from their favorite spots.
Harper picked Route 2 and Mount Monadnock as his favorite for foliage sightseeing, and Jeranyama takes in the turning leaves on his drive to Cape Cod.
In Franklin County, Reiber mentioned Mohawk Trail’s stretch into Charlemont. Walker kayaks at Cranberry Pond in Sunderland, where she watches the leaves change in the forest around her and their reflection in the water.
Keiser enjoys seeing the “rainbow” of fall colors at Harvard Forest where she samples soil.
“You don’t have to drive all the way to New Hampshire to get great foliage,” Keiser said, “or Vermont.”
