Falling now from a tree near you: acorns, walnuts and hickory nuts
Acorns bounce like ping-pong balls on the sidewalk. Hickory nuts plop onto the lawn. Walnuts fall with a thud on the ground. These trees are pummeling anything and everything below their branches. It’s enough to make you wonder if Chicken Little was right — perhaps the sky is falling?
The sky is not falling, but thousands of nuts are. The barrage of friendly fire is due to a phenomenon called “masting.”
Mast, in forest ecology lingo, refers to tree fruit. Hard mast comprises hard-coated nuts of all kinds, such as walnuts, hickory nuts, beechnuts and acorns. Soft mast includes dry seeds without hard husks. Maple seeds, mulberries and cottonwood fluff are examples of soft mast.
Unstealthy bombers, the hard mast producers can clobber you with their fruit. You may have considered wearing a helmet outside if you’ve been conked on the noggin already. It is a banner year for hard mast. Oaks are particularly prolific, and hickory nut production is way up. Squirrels, unconcerned with falling acorn bombs, are going nuts. Mice are up to their ears in nuts, and deer delight in the abundance of this high-calorie food. In short, wildlife is enjoying a windfall.
There weren’t this many acorns last autumn — why is this happening this year? The first part of the explanation of masting has to do with energy budgets. Trees either pour all their energy into flowers and fruit, or they invest everything in growth. There is no predictable schedule for masting, so it’s anyone’s guess about the next year’s crop.
Although this year’s investment has been in the production of a bumper crop of nuts, in 2012 it may all be directed to growth. Resources may shift from producing pollen to gaining girth.
The production of mast is an all-or-nothing proposal. Masting means that arboreal prodigality one year contrasts with Spartan austerity the next. It’s feast or famine for wildlife in any given year. In an “off” year, there are slim pickings for wildlife, with nary a nut on the ground. This leaves the squirrels to scratch their heads and say, “What gives?”
More realistically, it leaves the squirrels scrambling to find something else to eat. And this is part B of the ecological explanation of masting. The phenomenon of mast production is based on a “starvation-satiation regime” as research scientists Walter Koenig and Johannes Knopps explain in the journal Scientific American. The unpredictable boom-and-bust of masting is a way of faking out the enemy — or in this case, herbaceous predators. Lean years, with little to no nut production, force animals to diversify their diets.
Like Mom always said, don’t be a picky eater — eat what’s on your plate! If acorns aren’t on the menu, you’ll have to develop a more cosmopolitan palate. Thus squirrels will eat fungi, berries, leaves, buds — or raid neighborhood bird feeders.
In mast years, the amount of food available to wildlife is more than nut-hungry mammals and birds can possibly eat. These seed-eating predators are satiated in mast years. When the animals have stuffed themselves silly and cannot eat another bite, many nuts are left uneaten. An uneaten nut is a seed, and an uneaten seed is a tree-to-be.
Forest ecologists have proposed various cause and effect scenarios to explain and predict mast fruiting. Weather is likely to be an important cue for a mast year, but other factors certainly contribute. Researchers are still investigating the complex triggers for the production of mast crops.
Another puzzling aspect of masting is that trees across a large geographical area synchronize their fruit production. How does an oak tree in St. Charles “know” that it’s supposed to crank out acorns this year in conjunction with oak trees in, say, Elgin or Big Rock?
The answer is somewhat elusive. Scientists suggest chemical signaling, but that theory does not hold up for today’s fragmented forests separated by miles of shopping malls, highways and houses. Trees are too far apart in these disparate woodlands to be able to pass along chemical signals. Synchrony is a masting mystery that researchers are trying to solve.
Regardless of the unanswered questions, we do know that masting affects the forest community and beyond. Koenig and Knopps call this a “trophic cascade.” In other words, there’s a ripple effect from the little guys (herbivores) to the big guys (carnivores) and everyone in between.
Consider, for example, the following scenario: It’s a mast year, and acorn-stuffed mice are fat and happy. Deer, too, relish the extra helpings of acorns. Thus nourished, mice and deer produce lots of offspring, resulting in a mini population boom.
Enter the ever-unpopular tick. These eight-legged ectoparasites are particularly fond of mice and deer, and they benefit from the increased population of blood-bearing mammals. A portion of the tick population carries Lyme disease, and as the numbers of mice and deer increase, the number of ticks increases, and the probability of ticks transmitting the disease increases. Data from different parts of the country suggest increases in Lyme disease outbreaks following mast years.
There are more positive aspects of the trophic cascade from mast crops. For centuries before vending machines and fast food franchises, humans have gathered “slow food” in the form of acorns, chestnuts, hickory nuts and walnuts. And, from a hawk, owl, snake, or coyote’s point of view, an abundant crop of nuts leads to an abundant population of rodents, and this means fine dining for these top predators.
Acorn-laden oaks, bountiful hickories, and well-endowed walnut trees are providing a cornucopia of forest fruit this year. As these trees unload their mast, rest assured that the sky is not falling. The bounty will either be relished by predators or it will fall fortuitously in the forest duff. And therein lies the promise of the forest’s future.
Ÿ Naturalist Valerie Blaine is nuts about trees. A naturalist with the Forest Preserve District of Kane County, she leads guided hikes and tree identification programs throughout the year. Contact her with questions, comments, or cool observations of the wild world around you in Kane County: blainevalerie@kaneforest.com.