Why are there so many acorns this fall?

If you are walking under an oak tree this autumn on Long Island, one verb — duck — sums up best how to avoid becoming an unwitting player in an irregular fall phenomenon.

Fall 2023 has marked the return of masting, an occurrence every two to five years that yields an above-average output of acorn production, Long Island arborists said. For those caught underneath an oak, it means potentially coming into the line of fire of an arbor-like artillery of nuts raining down.

For Long Island and the rest of the Northeast, it also means more squirrels, deer and birds as well as growing concerns among arborists that development and climate change could exacerbate masting by overstressing trees to the point where a final massive acorn drop comes before an oak dies.

Experts can't point to a scientific cause of the cyclical outsized crop of acorns, but believe heavy rain, or droughts, can contribute to pollinated or stressed trees unleashing a large barrage acorns, or as the nuts are also known, fruit.

At Long Island wildland preserves, backyards and wooded streets, a legion of acorns has been raining down this fall, plucked by nature from oak trees — a welcome addition to the menu of squirrels, deer and birds, but posing a tripping hazard for humans, along with the occasional plunk on an unsuspecting head. 

“There’s no concrete scientific evidence or one attribute that contributes to a mast year,” said Michael Runkel, director of grounds at Hofstra University.

Even with Long Island’s wooded ecosystem, the region’s tree canopy is declining due to development and climate change affecting trees that normally produce acorns and beechnuts. Trees that may be stressed by warmer weather or drought or are dying may also shed a large number of acorns, Runkel said.

While experts said an acorn mast year is a normal phenomenon, some worry that shedding of the nuts amid the warming climate may be a sign of overly stressed trees.

At the 691-acre Bayard Cutting Arboretum in Great River, arborists are seeing a heavy supply of falling acorns from 40 different species of oak tree, said director Kevin Wiecks.

“Fruit production in trees and conifers is often a sign of increased stress. It’s something for us to be aware of and consistently, our native oaks have been under threat for a few years,” Wiecks said.

The warming climate has spurred the arboretum to experiment by planting trees that typically do better in southern parts of the country, he said. 

This season's masting event is expected to last for the next few weeks, said Melissa Finley, curator for woody plants at the New York Botanical Garden in the Bronx.

For all the concern, masting can also be a signal trees are healthy, Finley said.

“This year is on par with past masting years, and when I’m working outside I’m dodging acorns left and right,” she said. “It’s usually a good thing. It’s a sign these trees are functioning normally to develop such a strong flush of fruit.”

By John Asbury

john.asbury@newsday.comJohnAsbury

John Asbury is a breaking news and general assignment reporter. He has been with Newsday since 2014 and previously worked at The Press-Enterprise in Riverside, California.