Out In The Woods

It’s a big year for acorns.

Photo: Michelle McCarthy

Acorns and the Mystery of Bumper Crops

By Kevin McKeon, Director, Mousam Way Land Trust

What’s with all those acorns on the forest floor, all over your lawns, and in your gutters? It’s a good question, similar to the one asked about our bumper crop of pinecones this year. Both are rich sources of nutrients for new trees and for forest critters.

Oaks – like beavers, woodpeckers, and coyotes – are keystone species that play significant roles in our ecosystems. Oaks support more fungi, insects, birds, and mammals than any other tree. Earth holds about 435 species of the 56-million-year-old oak; about 90 in North America, and eight recognized as native to Maine. Trees can live to over 300 years old, and colonies of trees much longer; there’s a clone-colony of Jurupa oak in California whose birth is estimated to be during the last glacial retreat which was 13,000 years ago.

Oak trees are the subject of much lore and myth, and human history is rife with oak interactions. Iron gall ink is made from oak wasp galls and was used by Bach, Leonardo da Vinci, Rembrandt and Van Gogh. The Magna Carta and the Declaration of Independence are written with it. For thousands of years, acorns were an important food source and a symbol of strength for folks across several continents. Our pre-human Hominini ancestors dined on acorns. Oak trees were treasured above all trees and became a mystical link between Earth and Heaven for many ancient societies. Oak-leaved crowns adorned victorious commanders and royalty. Today, oak leaves medals are the symbol of many military ranks and are awarded for superior service and bravery.

But, back to all those acorns.

Often, a 15-year-old oak will begin making acorns, a process that takes two years for a red oak and one year for a white oak. Boom crops of seed, called mast years, cover the forest floor with nuts. Huge oaks that are masting can produce 10,000 nuts. But masting takes a lot of energy, so the following year, the tree prioritizes leaf production for increased photosynthesis to make food, gathering strength for the next masting.

Why does the tree do this? Survival to reproduce is the biological imperative of all living things. Evolutionary and environmental factors impact this primal drive. Ongoing studies of masting seek to answer that question. An 11-year University of California study of 10 separate sites over 434 square miles found that masting occurred in virtually all of the sites, approximately 100 million trees.

Several theories about masting have evolved.

The Predation Theory describes the reaction to intense foraging. With so many acorns produced, it’s found to be impossible for all of the seeds to be gathered, hoarded, and eaten by forest critters. The remaining seeds and many critters’ forgotten hoards can take root, ensuring propagation. This theory supports studies that find saplings of some species are mostly established during mast years.

The Stress Theory holds that trees stressed from environmental factors like drought or excessive heat tend to produce more seeds. Remember the two-year red oak acorns? 2021 had an average spring rainfall, but eight out of 12 months experienced moderate drought. 2021 is the year that red oak acorns now on the forest floor began their lives, giving credence to the theory that the stress of dryness two years ago led to 2023’s masting event. Also, 2023 had a late spring frost that killed a lot of white oak acorn blossoms. This would result in most of the acorns on the 2023 forest floor being red oak acorns, with the stressed white oaks maybe masting next year.

And then there’s a hormone called gibberellin, made by plants and the human chemical industry, that induces seed growth.

So, what’s with all these acorns? Scientists don’t know. Pick a theory, or maybe just enjoy the mystery and marvel at how nature cares for her trees!