In “Mast Years,” Trees Strategize by Overproducing Nuts and Seeds

That overabundance of acorns is not a mistake, but rather trees' coordinated effort to reproduce, affecting rodents, insects and humans.

by Karen Lanier
PHOTO: Shutterstock

Acorns are raining on us this year. Their pelting startles me awake from the rare afternoon nap as our large pin oak releases its protein packs noisily onto the metal roof and squirrels clamor for the abundant harvest. Last year and the year before were not so prolific, but I didn’t really notice. Until I tried sleeping through what’s known as a “mast year,” I’d never heard the term. The word mast refers to parts of plants that wildlife eat. When we use the word mast, whether we intend to or not, we are talking about ecology—the relationships of organisms to each other and their environment. A mast year refers to the periodic surge in production of hard mast (nuts and other seeds).

Mast Years Are Not Accidents

Oaks and other nut-bearing trees such as hickories and beech can produce a moderate amount of nuts regularly for between 2 to 12 years. Some years could be very lean or not productive at all. Every so often, they synchronize a release of stored sugars to push out scads (some estimate 100 times the normal supply) of fruit after their flowers were pollinated.

It’s hard to predict, but ecologists, hunters and naturalists theorize about when and how the bumper crops happen. Underground communication between trees of the same species might take place over a large, multistate region, sending the message through chemical signals that now’s the time to let loose.

Timing Is Key

Pollination is typically required for setting fruit, and the timing of insects, wind and freezing temperatures all play a role in the success of that step for fertilization. A late spring frost can kill the blossoms on white oaks and reduce or eliminate the fruit for that year.

It’s not quite that simple for red oaks. They take two growing seasons from flower to fruit, so the proof of their pollination is not seen until fall of the next year. That means we have to learn to identify our trees to know which ones had good luck with their flowers and when it happened.

(Hint: The leaves of white oaks such as bur oak, chestnut oak and post oak have rounded lobes, while leaves of red oaks such as pin oaks, black oaks and shumard oaks are more pointed.)

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oak leaves trees nuts acorns mast years

Seed Saving, Literally

If a tree lives for a few centuries, it might need to ration its energy output to stay strong for the long life ahead. There’s no need to waste energy reproducing if your offspring gets eaten anyway. So, it makes sense to wait until the predators are few enough that your seeds have a better chance of surviving. When predator numbers are low, trees can overwhelm them with more food than they know what to do with.

Squirrels and jays for example, will forget where they buried some of the acorns they gathered. Wild hogs might gobble up acorns without chewing and deposit them in rich fertilizer. Tree-predator partnerships could be used to the tree’s advantage as well. Sending squirrels farther away to forage for food means they might carry local nuts in their cheek pouches to places beyond the reach of the tree’s branches. Spreading the seed helps increase the diversity of the younger oak generations.

squirrel nut nuts mast year

Making the Most of the Mast

What do mast years mean for people who spend time hunting, foraging or just enjoying the great outdoors? Two things: feasts and diseases. If you are a hunter, you can relish the fattened wild hogs and abundant deer attracted to stands of masting trees. If you’re a forager, you can experiment with leaching tannins out of different types of acorns to make them edible and grinding them into nut flour for baking.

We’re not the only ones in the ecosystem thriving on the surplus. Rodent populations also surge. Next spring, there will be more mice and chipmunk babies in my backyard, and the following year we’ll have an increase in ticks and possibly tick-borne diseases such as Lyme disease.  Infected mice are the ones who spread the disease to tick larvae. (Note: Try these natural tick repellents.)

Such a small word—mast—contains a big and interconnected idea, like the calorie-dense gifts I now associate with the term. A mast year is not like someone amassing a fortune and blowing it in a spending frenzy. Rather, the trees have some kind of strategy behind the massive amount of acorns that drop onto my roof. Trees appear so benign and complacent to the world around them, but they really are calling the shots. Without the cyclical pulsations of mast years, organisms as divergent as weevils, woodpeckers and napping writers would function differently.

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