Local experts predict bright foliage after short delay

As fall continues, local experts expect the region’s leaves to blush with bright yellows, oranges and reds, albeit a bit later than usual.

“As always, it promises to be a lovely [fall] ahead in New England,” said Richard Harper, who teaches students about forestry at the University of Massachusetts Amherst.

The Massachusetts Department of Conservation and Recreation’s Interactive Fall Foliage Map, which can be accessed at tinyurl.com/DCRFoliageMap, forecasts peak foliage during the last week of October in Franklin and Hampshire counties, slightly later than normal in New England. According to the Old Farmer’s Almanac, leaves are typically most radiant in late September and early October.

Harper mentioned the rainfall in the summer and September as being a potential driver of the foliage delay. According to the Northeast Regional Climate Center, September precipitation in the Northeast piled up to 4.28 inches, 6% above the normal mark.

“There’s almost a little bit of a balance to the growing season with regard to precipitation and how that affects fall foliage,” Harper said. “Too much rainfall, you can end up with some leaf loss due to pathogens. Too little rainfall, the plants can shed their leaves because it’s so dry.”

Some scientists speculate that rainfall can dilute the leaves’ autumn hues as more moisture in the air leads to humid nights instead of the cool temperatures that trigger the leaves’ color change, Harper said.

Given the slew of environmental factors, Harper said it is difficult to forecast foliage.

Instead of leaves and trees, UMass Amherst Assistant Professor Ashley Keiser digs into the soil. While the samples for her soil testing showed signs of a dry summer in the past few years, this year’s samples have not set off the same alarm. She expects the periods of rainfall and warm, but not blazing, summer temperatures to usher in a bright fall.

“From a soil perspective, when [trees] have more moisture available to them, then there’s  going to be more movement during the growing season of nutrients they need — they’re not going to be (as) stressed,” Keiser explained. “Because of that reduction in stress and the access to nutrients that moves with water in soil, they’re able to prolong photosynthetic activity longer.”

Without water to deliver nutrients, it was not worth it for dry trees in the past few years to continue photosynthesizing, or converting sunlight, water and carbon dioxide into oxygen and energy. As a result, many trees’ leaves turned brown and dropped early, Keiser said. This year, with more nutrients from the rainwater, the leaves can photosynthesize and survive longer, giving them the energy and time to change color before dropping.

Keiser added that many trees in the region survived the September nor’easter’s strong winds — a promising sign of rich soil and bright foliage ahead.

According to Harper, the ideal ingredients for flashy foliage include moderate rainfall and temperatures, and crisp nights that dip thermostats into the high 30s and 40s.

“Most importantly, you need the right plants,” Harper said, “and one of our monarchs of the fall color is a sugar maple.”

The sugar maple tree earns its fall fame from its mixture of the three chemical compounds behind foliage — carotenes, xanthophylls and anthocyanins, Harper said.

As types of carotenoids, carotenes and xanthophylls lie within the tree’s leaves already, but the green chlorophyll hides the carotenoids in the spring and summer. In the fall when the shortening daylight and cool nights trigger the tree to cut off its “support system,” the chlorophyll breaks down and the leaves die, according to the University of North Carolina at Chapel Hill. Only then do the oranges of the carotenes and the yellows of the xanthophylls finally have their time in the sun.

For the reds, the leaves of sugar maples and other scarlet trees “manufacture” anthocyanin.

“So you have three things going on with sugar maples,” Harper said, “which is pretty cool.”

Besides “the classic sugar maple,” Harper keeps his eyes peeled for the golden needles of tamarack and larch trees in the fall.

Keiser called the golden ginkgo trees on the UMass Amherst campus one of her favorite fall fixtures. Since the trees’ leaves drop quite suddenly, “It’s a really fun game to think about when the leaves are going to be lost,” she said.

To Keiser, the secret to New England’s star foliage is the region’s cast of characters.

“You’re going to get this nice, slow change of color, and then they’re falling at different times, so they’re not disappearing all at once,” she described. “The birches are turning yellow, and they’re dropping to the ground early, and then we’ll get our maples dropping, but those oaks will hold on longer, so we get this wonderful complexity that composes our northern hardwood forests.”

For Harper, New England’s leaf-peeping reputation comes down to the right environment, the right trees and the right people.

“We’ve got the folks around who enjoy it, and on top of that, we have the agricultural economy for this,” Harper said. “What’s the classic New England thing to do? Go to an orchard this time of year, have cider, a cider doughnut and enjoy the lovely fall foliage. … People come from all over the world to see what we enjoy and almost take for granted every year.”