Illustration by Ned Barnard

by Ned Barnard

Every day, my wife and I walk to the coffee shop for our cappuccinos. On the way, I’m always looking at trees and things they drop on sidewalks and streets. This year, something is going on with our oaks – at least with red oaks and black oaks. They’re dropping many more acorns than they’ve dropped the past two or three falls. And almost every red and black oak I see is doing this.

Years with gluts of acorns are called “mast years” and are usually restricted to a specific oak species, or to two closely related ones like red and black oaks. People who study trees – dendrologists – attribute mast years partially to weather conditions. Oaks are wind pollinated, so if the spring weather two years ago (red oak and black oak acorns take two years to mature) was particularly wet and windy, then maybe an unusual number of red and black oak flowers would have been fertilized.

But weather conditions may not be the whole story. Oak mast years tend to occur over large regions in which weather conditions may vary from place to place. In 2015, for example, a mast year occurred in an area stretching from New England to Pennsylvania.

Dendrologists think a mast year may be a survival strategy to counter predation. If a huge number of acorns are dropped in a single season, then mice, squirrels and other acorn-eaters probably won’t gobble up all the acorns, and a few more acorns may sprout into seedlings.

And leaner acorn production years in between mast years probably help restrict rodent populations and allow trees to channel more energy into wood production. Do oaks somehow keep track of time or communicate in ways that allow them to synchronize their masting intervals? Are they texting to coordinate acorn drops?

It is certainly amazing that so many of them produce acorns simultaneously.

Ned Barnard is a Hill resident and author of several books on trees, including “Central Park Trees and Landscapes” and “Philadelphia Trees.”