Gardening Essentials – Lessons in Acorn Economics
I have a complex relationship with my side yard oak tree. It stands at the south end of our house, canting its elegant branches out toward the light and away from the pines, and casts its cooling shade on our roof in summer. In winter though, at night, which lasts most of the day in January anyway, I lie wide-eyed in the dark, convinced that one of its massive main boughs is about to crash through the roof and crush us in our bed. I have considered, at such times, fleeing to sleep in the basement.
What is perhaps most unpredictable about the oak tree, however, is its behavior in the fall. Some years the yard is pocked and pitted with the impact craters of hundreds and hundreds of acorns. Once, having parked my car under that oak, I came out in the morning to find the rear windshield spider-webbed in cracks; under the constant rain of nuts, one acorn had hit it in the weakest point, at the corner. Other years, the harvest is scanty. This is mostly a matter of curiosity for me, but one of life and death for the squirrels, turkeys, jays and other creatures that exploit this unpredictable resource. The boom years of the acorn economy are referred to as mast years. “Mast” refers, technically, to any food source used by wildlife, but the main categories are hard mast (acorns and beechnuts in this region), and soft mast (like berries).
The prevailing wisdom is that the unpredictability of mast years is adaptive for the trees. In lean production years, it’s tough to make a living as a squirrel, for example. Fewer young squirrels survive in those years of scarcity, and the population overall stays on the small side. An oak mast year comes, and while many of the acorns do get eaten, the small squirrel population can’t possibly eat them all, so at least some acorns manage to sprout into baby oaks. The squirrels eat as much as their bellies can hold and the surplus takes root, and the next spring and summer we have a bumper crop of healthy baby squirrels that will be off foraging for acorns themselves in the fall.
This happened a few years ago, when it was hard even for the most indifferent wildlife watcher not to notice an outrageous number of squirrels everywhere. In yards, at bird feeders, crossing the roads, failing to cross the roads and piling up dead on the median strips and gravel shoulders. This was the baby boom, and the generation before them, fat and happy on last year’s acorns, discovering that this fall there were few to be found. The oaks that had been the source of so much beneficence now had withdrawn their largesse, and the stingy crop left the rodents scrambling for something to eat, ranging farther and farther in their hunger and dying in droves, and down fell the population once again. The cycle repeats, but not with any kind of predictable regularity, or else the squirrels’ reproduction would align with the oaks’.
This year and last were not mast years. I have found few acorns sprouted in my garden beds, rupturing their shells like fists inside a tight glove, split across the knuckle. Mostly it’s been maples making a go of it this year. The squirrels will eat maple seeds, too, but they can’t compare to acorns for caloric density. The squirrels live as I live, their fates entwined with the trees’ capricious whim. Come winter, in the wide-eyed dark, I try to accept what the squirrels are forced to: live by the oak, die by the oak.