The fruit of the oak

The fruit of the oak

By Dr. Robert A. Hedeen, Naturalist

The science of botany recognizes many different types of fruits that enclose the seeds of the plant: drupe or stone fruit (plum), berry (grape), ppome (apple), achene (sunflower), grain (corn), samara (maple), and nut (acorn).

The most important fruit of the forest, in terms of what it yields to the woodland community, is the fruit of the oak, the acorn. There are nearly 60 different species of oak to be found in the United States, and all produce acorns of one type or another. One thing all acorns have in common is their amazing food value. They are rich in carbohydrates, fats, proteins, and vitamins. Most other nuts (hickory, walnut, beech, chestnut) have a tough shell and must be consumed by animals with strong jaws and gnawing teeth. The acorn, however, has a relatively thin outer covering and is seated in a cup, and it is one of the staple items in the diet of many insects, birds, and mammals.

On the average, oak trees produce bumper crops of acorns about once every three or four years, and that means full bellies for the year for acorn-loving animals. In poor production years when the acorn crop is lean, many of these animals are hard pressed to survive during the winter.

An oak averages about 5,000 acorns a year, and a study made some years ago by foresters found 85 percent of the nuts were eaten by mammals and birds. Weevils, and other insects attacked another 12 percent (an acorn with a small symmetrical hole in it indicates it was attacked by a weevil that devoured the meat inside). As another 2-3 percent were found to be imperfectly formed, they calculated that less than 1 percent of the acorns germinated, and of the few that did, half died as seedlings. Thusly, oaks adhere to the basic law of nature that, in all species, more offspring are produced than can possibly survive. The forces of natural selection determine the fittest and best adapted to live and become the parents of the next generation. A female oyster, for example, may produce 500,000,000 eggs that are nearly all fertilized by the billions of sperm cells produced by a male during a single spawning season, but only four or five will eventually develop into a mature bivalve.

In the past, humans have used acorns extensively as a source of food. The early settlers of North America quickly learned from the Indians that acorns could save them from starvation. All acorns contain a bitter substance called tannin, with some acorns containing more of this material than others. The acorns of the white, chestnut, and live oaks contain very little and may be eaten as is. Acorns of the black and red oaks amass a considerable amount of tannin in the tissues and are quite bitter to the taste.

The Indians learned, and passed on to the white man, that by boiling the bitter acorns in water to which wood ashes had been added, most of the obnoxious tannin could be leached out. After boiling, the acorns were dried and pounded into a meal or flour.

Acorn meal was added to soups or made into a concoction that was similar to cornmeal mush. Sometimes acorns were ground up and brewed as a beverage. Acorn coffee was a common beverage of Confederate soldiers during the Civil War when they could not trade tobacco for coffee with their Union counterparts.

Squirrels, chipmunks, and some birds, especially the blue jay, secrete acorns away for the winter. This ritual benefits the mighty oak as well, as many forgotten acorns end up as seedlings. Some scientists have suggested that this ritual of burying acorns is responsible for oaks re-establishing themselves in parts of North America after the glaciers that denuded the land of trees as they passed over it melted, and the landscape reverted to one conducive to vegetation.

“Mighty oaks from little acorns grow,” but those that do not make trees make other valuable contributions to the natural world.

Dr. Robert A. Hedeen is a former resident of Maryland’s eastern shore and resided in the Chicago area from 1960-1971. He is a retired professor emeritus of biological sciences in the University of Maryland system. He has published more than 30 scientific papers, has written numerous magazine articles, and is the author of two books on the natural history of the Chesapeake Bay.

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