Nuts for Acorns

I collected these acorns on the grounds of the Bruce Museum.

It’s a good time to be a squirrel. You might have noticed that there are more acorns around than usual this autumn. That is because we are currently experiencing what is known as a mast year. During an oak mast year, oak trees produce more acorns than usual. Normally, animals eat most acorns before they can sprout. In a mast year there are too many acorns for even the hungriest deer, birds, and mice to eat.

Mast years are somewhat mysterious to scientists. Different tree species mast at different times. We are having an oak mast right now, but chestnut trees and hawthorns may mast another year. What really puzzles scientists is figuring out what factors provoke a mast year. They don’t seem to be correlated with temperature or rainfall. Some trees mast when triggered by forest fires, but most are on seemingly random 2 – 5 year cycles. 

The impact of a mast year can be felt across the entire ecosystem. Increased availability of food prompts population surges in mice, deer, and other acorn-eating animals. This makes more prey available for predators and parasites, so their populations also increase. One such parasite is the black-legged tick. Ticks are related to spiders and feed on the blood of mammals and birds (sometimes reptiles and amphibians too). Unfortunately for humans, ticks enjoy the taste of our blood as well. Even more unfortunate is what ticks can carry – Lyme disease. Cases of Lyme disease spike during and after mast years.

If you ever are bitten by a tick, save the tick after you remove it. Doctors can test the tick for Lyme disease to see if you might be infected. Image by Kaldari.

Though mast years mean more deer chomping on gardens during winter and more Lyme disease, it isn’t all bad news. Historically, mast years have been favorable for humans. People would let their pigs roam the forest during masts and fatten themselves on acorns. Many Native American tribes benefited more directly and ate acorns as a major part of their diet. However, for humans, eating acorns can be complicated.

Acorns have a compound called tannin in them. Tannin is found in low quantities in tea, wine, and some cheeses. In moderation, tannin can improve health by serving as an antioxidant and preventing heart disease. Some acorns have relatively low tannin levels and can be eaten with little preparation. The acorns with higher concentrations need to be processed before they can be eaten.

The acorn of the white oak is low in tannin and has a pleasant nutty flavor. These acorns are favored by humans and animals alike.

At high concentrations, tannin makes food difficult to digest and adds a bitter flavor. Native Americans wishing to enjoy an acorn bounty had a variety of methods to reduce the tannin content. Some tribes soaked acorns, whole or after being pounded into flour. Processed acorns could be stored in granaries and eaten throughout the winter months.

High-tannin acorns can be difficult for animals to digest too. Many animals simply eat more acorns to compensate for the loss in digestive efficiency. Animals more sensitive to tannins like horses and cattle may experience acorn poisoning and need to be fenced away from oak trees to prevent ingestion.

Sudden death can occur in cows that have eaten too many acorns. 

If you are feeling adventurous and want to live like a squirrel, there are many guides available online for the best acorns to eat, and how to prepare them. Otherwise, keep an eye open for a bumper crop of oak seedlings in the spring! 

- Kate Dzikiewicz, Paul Griswold Howes Fellow