Berkeley parks

Why are there so many acorns in Sonoma County this year?

You may have wondered about the din on your roof, the piles around trees and the hyperactivity of squirrels in your neighborhood.

In Sonoma County, a mass event takes place at dusk tonight: hundreds of thousands of greedy creatures are picking up treats – not the sweet variety, but an unusual bounty of oak acorns.

Many massive oaks in Sonoma County are reported to be unusually loaded this year. A large number of shiny brown conical nuts began to fall on the roads, sidewalks, terraces and woods. And it attracts a large assortment of hungry wildlife, from black bears to wood ducks.

The massive acorn bonanza isn’t just a local event. Mysteriously, observers say, the oaks across the region, some over a hundred miles apart, all produce a bumper crop at exactly the same time. It is a synchronized natural phenomenon called “masting”. And science has yet to understand why and how this happens.

Paul Weber saw this happen as a member of the Natural Resources Division of Sonoma County Regional Parks. Weber has practical experience in oak forests, having restored and managed vegetation in county parks.

“I’m seeing a big acorn harvest this year in the parks,” he said, “from Sonoma Mountain to Ragle Ranch Park, especially black oaks and live oaks.” Those falling acorns are a good source of new trees, Weber said. Park staff collect them to restore forests and replace old and aging trees.

Brent Reed, head of restoration projects at the Laguna de Santa Rosa Foundation, also sees a larger acorn harvest.

“It looks like a very good year for the oaks in the valley,” he said. Like many residents, he also finds acorns that accumulate in yards and break under the tires in parking lots around Santa Rosa.

Various theories

So what is masting and why do oaks do it? There are a number of theories, Reed said, but it’s still something we don’t fully understand.

We know that ripening occurs in many species of oaks and some other plants, in apparently unpredictable patterns. Trees can go for years with low or modest acorn production, then hundreds or thousands of trees will suddenly produce a boom crop all together, like at the right time, over large sections of the landscape.

In the late 1970s, the mysterious behavior of oak trees caught the attention of Walt Koenig, now a senior researcher in animal behavior at Cornell University and a zoologist emeritus at UC Berkeley.

Koenig sought out the peculiar antics of Acorn Woodpeckers – they breed in mixed clans, collectively store acorns in precisely pierced logs, and go to war to defend their territory. He also decided to investigate what might cause the ancient oak trees they live in to act in seemingly synchronized ways. At the time, few people wondered why.

“In fact, oaks were easier to hunt; they don’t move that much, ”Koenig joked. Forty years ago, he said, he started a project to count acorns on individual trees every year. Eventually, he was counting acorns on oak trees scattered over hundreds of square miles of central California.

Valley Oaks, Koenig learned, had synchronized mast years across most of their geographic range, hundreds of miles apart. But there was no obvious explanation for how they achieved such a feat.

Various theories have been proposed. Maybe masting is a last resort response to stress or threats like drought or fire. Or is it a strategy to overwhelm acorn-eating animals with many acorns so that they survive to germinate again? Or do trees shift their resources after years of growth into a single year focused on seed production?

The theories are still hotly debated, Koenig said, and there’s probably a very complicated combination of factors at play. But he sees strong evidence pointing to the influence of time.

“We know that acorn production is correlated with the weather,” he said. “And in particular, after a hot and dry April, they are doing very well.” April is usually the month when acorn flowers are pollinated.

There are tantalizing clues that hormones or other chemical communications may be involved. There is also evidence to support the “predator satiety” theory, Koenig said: the idea that more acorns will become seedlings if the animals that eat them are overwhelmed by a large number of acorns at the same time. time.

Food chain

A surprisingly wide range of California wildlife depend on oak acorns for food, explained Reed of the Laguna de Santa Rosa Foundation. Not just dozens of bird species, but also rodents, foxes, deer, bears and insects.


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