Michael Ellis: A Bumper of Acorns

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People with oak trees on their property may have noticed that its not only raining the wet stuff this year – It's raining acorns. Michael Ellis explains.

In 17th century England a bumper was a large wine glass filled to the brim. “Aye, I’ll have another round of bumpers for me buddies.” Eventually it came to mean a lot of anything, unusually large, but not just wine. Now we use it mostly when referencing a “bumper crop.” And this year many have noticed a bumper crop of acorns.

Beginning a month ago it was literally raining acorns in my backyard from two magnificent oak trees. Both the deciduous valley oak and the evergreen coast live oak dropped thousands, yes thousands, of nuts. It was hard to walk on my deck!

Friends all over the Bay area reported the same spectacle - a biblical flood of copious acorns.

The official term for this periodic explosion of seeds is ‘masting’. Many species of trees and shrubs do this, not just oaks. But since oaks dominate in many California habitats we really notice their effect. Scientists aren’t clear what causes masting but it is surely related to ideal environmental conditions during the spring when the trees are in flower and setting fruit. One statewide study found oak groves from different species 180 miles apart synchronizes their masting! How does that happen?


The evolution of this phenomenon may have something to do with predator satiation. In other words, the myriad of animals that eat acorns will be overwhelmed by the sheer total available. Therefore, many acorns will survive and propagate more oak trees. And during the years of low seed production the numbers of seed eating predators will be kept low. At least that is one boom or bust theory.

In 1990 the California legislature found that California’s oaks help define our landscape. ‘Golden hills dotted with deep green trees’, they called it. And in recognition of their many benefits to livestock, wildlife habitat and our own enjoyment, declared the first Friday in November—California Oak Day.

Hey, that’s today! I’ll drink a bumper to that.

This is Michael Ellis with a Perspective.

Michael Ellis is a naturalist living in Santa Rosa.