While blazing a trail on the King Nature reserve with Tom Pearson on September 4 I came upon the first ripe shagbark hickory nuts of the season. Collectively, the entire nut crop is known as mast. This crop is very important to wildlife because it provides a major source of food, but it is also the trees' method of reproducing. Trees are thus confronted with a major survival problem. If animals eat all of the trees' mast there will be no young trees to replace the older ones which die of disease or get blown down by the wind. Given time, this will spell extinction for the tree. The fact trees survive today means they have figured out some means of preventing their entire nut crop from being eaten. Trees, of course, have no brains for figuring out a strategy. These methods have come about by the process of natural selection.
There are several ways trees can assure their nuts escape being eaten by foraging animals. One way is to make the nut bitter and unpalatable to the taste buds. This is one of the strategies used by the red oaks who load their acorns with bitter tannin. Another way is to germinate as soon as you hit the ground giving the foragers little opportunity to find and eat the nuts before they grow into young seedling plants. The white oak employs this method. Most interesting, however, is the widespread synchronization of the trees in crop production. Perhaps you have noticed that there will be great numbers of acorns in some years, but practically none in others. Beechnuts might cover the ground one year and be totally absent for several years afterwards. Rarely do you see a fraction of a forest's oaks producing acorns. It's all or none. If just a few trees produce a nut crop, foraging animals will home in on those trees and eat everything. None of the nuts will survive to grow into trees and the parent trees will have wasted their energy, but if all the trees produce a massive nut crop the same year there will be too many nuts for the foraging animals to eat and a few nuts will survive predation to grow into trees. Trees producing small seeds don't have this seed predator problem and produce seed every year.
I used to believe since most of the mast producing trees flower in the early spring that spring frosts were responsible for a small nut crop in the fall. Heavy frosts when the trees are in flower in the spring no doubt affect the size of the mast crop, but there have been many exceptions to this scenario. I have seen years of little frost and still no acorns or beechnuts. When all factors seemed ripe for a banner crop year, there was no production. There appear to be years when the trees do not produce no matter how good the conditions.
On the other hand, a massive nut crop to overwhelm the predators has a distinct disadvantage. It will mean a lot of food for the mast predators and more nut eating animals the following year. Higher populations of squirrels, chipmunks and turkeys would be capable of eating all of even a heavy crop. Consequently, by not producing a big nut crop two years in a row, the trees will starve the nut predator population.
Red oaks produce acorns every other year. Beech mast crops are heavy only every five to seven years. Game biologists have also noted that squirrel populations seem to fluctuate with the acorn crop. Squirrels also alleviate the trees problem by burying nuts for future winter use. Nuts not retrieved from this cache may germinate into trees.
Birds are also nut predators. This past winter was the year of the super invasion of wintering finches. Pennsylvania was over run by crossbills, siskins, nuthatches and grosbeaks. There was a massive pine cone crop failure all across Canada driving the finches south for the winter into Pennsylvania where our spruce and pine trees did have cones. Thousands of crossbills over wintered in Cook State Forest this past winter season. All the birds mentioned feed on conifer seeds.
There seems little doubt that trees employ the strategy of overwhelming the nut predators with food one year and then starving them the next to hold down their population. Although the tactic arose by natural selection, it is a mystery how all the trees of an area seem able to synchronize their mast production to fall on the same year. Just try and find a rogue tree in the forest that is yielding nuts when all the others are not. Such a tree, of course, would be wasting its energy because none of its crop would escape being eaten. You can watch for these synchronizations in the parks and preserves of Murrysville. Take notes on spring conditions and watch what happens in the fall. Such observations require years of note taking because I have over-simplified the case. Nature has many well kept secrets.
