The mystery of masting

It’s the classic harbinger of fall: the thump of black walnuts and the ping of acorns as they rain down from the tree canopy.

This year my street has the usual track-marks of acorn paste on its surface, but there aren’t nearly as many nuts as there were last year, when we all tried to avoid parking under the oaks to keep our cars from getting dented. It’s strange that some years there are almost no acorns on the ground, while in others the street is flooded with them. What gives?

The term for this phenomenon is masting- when on occasional years populations of nut-bearing trees produce a huge number of seeds. It’s a clever adaptation. If all the trees of a particular variety overwhelm their environment with seeds, at least some of them will avoid being eaten by satiated predators, and will survive on the ground to germinate.

In Europe masting has been well-observed since the middle ages. People have actually tracked mast years for centuries, trying to find a pattern or codify what precipitates them. But what stymied pig farmers in the middle ages confounds scientists and naturalists today.

Somehow the trees are communicating with each other to synchronize a massive reproductive effort. Is it a chemical signal? A response to something in the environment? Weather? So far no one knows, and it’s kind of interesting to think that after studying a simple natural phenomenon for hundreds of years, we still don’t understand it.

As I walked around my neighborhood, I noticed that it’s the beech trees that seem to be masting this year. In some places the sidewalk is hidden under a carpet of beech husks and exposed nuts, too many for our teeming population of squirrels to keep up with.

The mystery remains, literally underfoot.