This Oct. 4, 2023, image provided by The Morton Arboretum shows an abundance of fallen acorns under an oak tree in Lisle, Illinois. (The Morton Arboretum via AP)This Sept 12, 2023, image provided by The Morton Arboretum shows a white oak tree bearing a bumper crop of acorns during a mast year in Lisle, Illinois. (The Morton Arboretum via AP)This Oct. 22, 2023 image provided by Julia Rubin shows black walnuts under a tree in Westchester, NY.
Nut-bearing trees, like black walnuts, beeches and those acorn-producing oaks, have “on” and “off” years. “On” years, called mast years, see vigorous production of nuts across an entire species throughout a region.
During mast years, a single oak can drop thousands of acorns, forcing you to rake your lawn even before any leaves drop, or sweep your driveway to avoid twisting your ankle while navigating a blanket of marbles. headtopics.com
After expending all that energy on an abundant crop, the trees take a break, producing few if any nuts during “off” years.Crane removes famous tree by Hadrian’s Wall in England that was cut down in act of vandalismThe cycles for mature red oaks and black walnuts typically run two to five years; pecans tend to alternate between boom and bust, often taking just one year off. Most fruit and nut trees undergo these cycles, although each species has its own timeline.
“There’s no general consensus (among scientists) on why we see these mast years,” according to Jonathan M. Lehrer, associate professor and chair of the Department of Urban Horticulture and Design at Farmingdale State College in New York. “There’s a lot of conjecture that it’s caused by variations in temperature and natural rainfall, but we’ve never been able to hammer out exactly why some years have greater production than others. headtopics.com
The phenomenon also affects the wildlife population, as bumper crops during mast years provide abundant food for woodpeckers, deer, mice, wild turkeys, squirrels and other animals, resulting in more breeding. Less food during off years tends to keep those populations in check.