Saturday, 11/24/2023

Going Nuts? It May Be a Mast Year

Black walnuts sit under a tree in Westchester, New York. Black walnut trees made a lot more nuts than usual this year. (THE ASSOCIATED PRESS)

Trees in some regions are going nuts this fall.

Acorns are bouncing off houses and heads. Walnuts are covering walkways. Pecans are hitting parked cars.

Why are we being shelled with nuts? Experts say trees that produce nuts have “on” and “off” years. “On” years are called mast years. That is when trees produce more nuts than normal.

That takes a lot of energy. So the trees also have “off” years. They take a break. They produce few nuts or no nuts at all. That cycle affects all trees in a species across an entire region.

Experts Are Still Stumped

This is an “on” year for black walnut, beech, and oak trees. Just one oak tree can drop thousands of acorns. That makes it harder to walk without twisting an ankle. In cities, they have to be raked.

Most fruit and nut trees have “on” and “off” cycles. Each species has its own. But even experts don’t know the reason for mast years.

Jonathan Lehrer teaches at Farmingdale State College in New York. He said some think mast years are caused by changes in rainfall or temperature.

“But we’ve never been able to hammer out exactly why some years have greater production than others,” he said.

The Role of Mast Years

But experts do know the “on” and “off” years are important for trees and wildlife.

Acorns and nuts have seeds. When nuts fall, those seeds take root to grow more trees. That keeps the species alive.

Mast years also provide food for squirrels, mice, and other small animals. Then they have more babies. Less food in “off” years limits the number of them. That also affects larger animals that eat small animals.

Lehrer said a big acorn drop may be a pain for humans. But mast years are important in the natural world.

We just have to remember to look up!



  • shelled v. hit with weapons
  • affects v. causes a change
  • species n. group of animals or plants that are similar and can produce young animals or plants
  • hammer out (idiom) find the reason for something

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