What tells forests to produce lots of nuts/berries one year but not another?

Foresters and biologists use the innocuous word “mast” to describe the production of wild nuts and berries in woods and fields. The amount of mast fluctuates each year and has wide-ranging effects: In a good mast year there’s lots of natural food to be had so bears are less likely to be lured to your bird-feeder and hunters will have more trouble finding well-dispersed deer when archery season opens and mice will be fat and happy, reproducing wildly and and, alas, thus becoming more likely to wander into your yard and drop some Lyme-carrying ticks.

There are pretty good explanations for why individual trees would have wildly varying seed production from year to year: The most accepted theory is that it evolved to thwart predators that eats seeds, like squirrels. Low-mast years starve the predators and reduce their population, then high-mast years overwhelm them, meaning that more seeds remain uneaten and can grow.

But what makes multiple trees, and even multiple species, synchronize their mast production? In general, all trees and shrubs and plants have good seed-production years and bad seed-production years in tandem. There are advantages to this, since forest-wide shifts increase the effect on seed predators, but what tells them how to get in sync?

Research at New Hampshire’s Hubbard Brook Experimental Forest has produced a theory: “When summer temperatures in two consecutive years are very different, then high seed production occurs in the following year. One clear advantage of synchronous flowering in wind-pollinated trees is that waste of pollen is reduced, and this explanation may contribute to the selective value of masting, particularly for species that are not primarily dispersed by seed predators (e.g., sugar maple is wind dispersed). The same cue has been observed in wind-pollinated Australian forest trees.” Check it out here.

I learned about this from the wonder magazine Northern Woodlands, which reported on it in the latest quarterly issue. It’s not online yet, but if you’re at all interested in forests and forestry you should absolute read it. I’ve never seen such a great mix of the super-practical (how to sharpen an ax), the meditative (columns about the joy of seeing flowers), the biological (the latest issue has photos of carrion beetles burying a dead mouse!) and the technical (apps for ID’ing species).