It's Raining Acorns

Has your noggin been bopped by one yet? For the past few weeks, oak trees have been pelting rock-hard acorns down onto the unwary. Walks in the woods have involved ducking, cringing, and holding hands above the head while trying to avoid these merciless missiles.

Acorns are irksome once they reach the ground as well. They're constantly funneling down into the trails and feeding ever-growing pools of slippery, rolling mayhem. Stepping into one of these traps can lead to a cartoonish flailing and scrambling for solid ground.

What's going on? It's a mast year for oaks. This means that most of the oaks in the area have produced far more seeds than usual. Various tree species have mast years. Last autumn it was beech's turn. Oaks have mast years every 2-5 years. This year's mast has created more acorns that we've seen in decades.

Masting takes a lot of energy, so why do trees do it? The short answer is 'safety in numbers'. A masting forest of oaks produces far more acorns than even the hungriest army of squirrels, chipmunks, mice, deer, bears, and others can possibly consume. A few seeds are guaranteed to survive and grow into new trees.

There are further subtleties at work. Small critters like squirrels, chipmunks, and bluejays store acorns in caches. Tons of acorns mean loads of caches to remember. Some caches are inevitably forgotten.

Bluejays, in particular, provide a useful service to the oaks that they plunder, by helping the trees disperse their seeds. A single bluejay can stash thousands of acorns in a season, carrying them several miles from the parent tree.

Bluejays are often an important factor in the dispersal of oaks to new locations.

Masting depends upon synchronicity among trees. It's no good if you're the only tree making acorns. You need your neighbors to get in on the act, so your predators are sufficiently swamped with food. How do trees manage it? Intriguingly, scientists don't really know. It could be a combination of environmental factors including temperature and rainfall. It's also possible that trees send chemical signals to one another that enable them to coordinate their activity.

It's likely that the acorn rain is mostly done for this year, thanks to the very blustery weather we've had in the past week. Unfortunately, the winds also brought down a flurry of leaves, and these have effectively hidden many of the roly-poly traps.

Masting is an exhausting business for trees, and it's likely that next year will be largely acorn-free as the oaks recover. Perhaps you can take some comfort in this if you find yourself rolling about or getting bonked by a few final acorn missiles.