The other day it was warm and windy. At home, I had the windows open and with every gust of wind I could hear the acorns steadily falling onto the backyard picnic table. I noticed in the mid-summer that this year would be a bumper crop of acorns. Our oak tree’s bottom limbs were almost touching the ground by late July. But it isn’t just our tree – tree’s all over central Oklahoma have produced massive quantities of acorns this year – a mast-fruiting year!
Every few years something in the environment triggers large nut production in trees across a wide area. It was thought that trees produced a giant nut crop in years that had excellent growing conditions – taking advantage of abundant sun and rain to make a bunch of seeds. Then on not so good years the crop would be small. However, during non-mast years resource (sunlight and rain) are often as good as mast years with trees spending effort on increasing their size. It is still a bit of a mystery as to how all the trees “know” to produce lots of seeds in the same year. Masting can be observed over wide geographic areas – up to 1000s of kilometers! Biologists suspect that trees are responding to a widespread climatic anomaly, maybe an El Niño type weather pattern.
But why would trees have evolved to all fruit in one year? The best explanation is to satiate seed predators. On years where there are ten times the number of seed produced, the seed predators – birds, squirrels, mice – have way more seeds available than they can eat. There are some really interesting biological cycles that affected by masting. As you would guess, a masting year would cause a boom in the seed predator population. Yet, in the coming years all those predators can’t find enough seeds to eat and instead eat insect larvae, bird eggs, and other omnivorous goodies. Those populations in turn decline. In fact, disease ecologist, Richard Ostfeld, linked the incidence of Lyme disease (a tick carried human disease) to oak masting.
The phenomenon of masting, yet again, reminds me of how little we perceive or understand of the patterns that govern that natural world around us.
So when you are scooping acorns out of your gutters this winter, just we thankful that your task won’t be as big in the coming few years!
Read more from the experts!
The best article I have read on tree masting, and the source of my woefully inadequate summary: The Mystery of Masting Trees by Koenig and Knops, American Scientist 93:340-347
You can also read more about Koenig’s work on California acorns on his website.
Full article about Lyme Disease: The Ecology of Lyme Disease Risk by Ostfeld, American Scientist 85:338-346