Last year’s mild winter has led to a bumper crop of acorns this fall — all you have to do is look down.
“By this time of year, acorns will start dropping and you’ll see them scattered all over the ground,” said Jalene LaMontagne, professor of biological sciences at DePaul University.
While the autumnal occurrence is nothing new, this year’s abundance in acorns has proven exceptional — the result of a “mast seeding event,” a phenomenon that only happens once every few years in which oak trees produce a much larger amount of acorns than normal, local experts say.
“The same species of tree coordinates and produces a ton of their seeds and drops them at once,” said Jessica Turner-Skoff, science communication leader at The Morton Arboretum. “It’s very location-specific, and it’s a really interesting phenomenon that has huge ecological effects.”
Chicago and its surrounding areas are currently seeing one of these mast years, and although experts haven’t figured out why it happens, there are a few theories.
One possible explanation is “predator sedation,” says Turner-Skoff.
This means that oak trees might produce an overabundance of acorns so that animals won’t eat them all, leaving extra hope for one of those seeds to grow into its own tree.
But this also means more food for the animals that eat them — one reason you can expect to see more baby squirrels running around come spring.
LaMontagne says the surplus in food can increase a species’ chance of survival, especially for those that store it over the winter — like squirrels — ultimately aiding in their reproduction.
“Their population will increase over time, and then what eats them can also increase. It’s this really crazy cycle that, down the line, has an effect on the predator-prey cycle,” Turner-Skoff said.
Another theory on what prompts a mast year? Timing.
Producing acorns takes a lot of energy from trees, and pumping out mass quantities could result from environmental cues or phenology — the timing of life events — that prompt trees to boost up seeding.
“Those cues can signal to the tree that this will be a great year to reproduce because they have all the nutrients needed to grow them,” Turner-Skoff said.
Northern Illinois saw a relatively warm and less snowy winter than usual, according to Brett Borchardt, senior meteorologist at the National Weather Service.
Most years, wind-pollinated trees, like oaks, don’t produce many seeds, but if the weather is warm in the spring, then the tree will grow more flowers than leaves, and each flower has more potential of being pollinated and eventually turning into an acorn, LaMontagne said.
“Oaks can grow thousands and thousands of acorns, but next year there aren’t going to be very many,” LaMontagne said.
There are 55 species of oak trees that are native to the United States, 20 of them just in Illinois. Other wind-pollinated species that also have mast years include walnut and hickory trees.
“I encourage people when they’re out or in their neighborhoods to look up at the trees,” LaMontagne said. “We won’t see this again for a while.”
