acornsDecember 11, 2018

It Is obvious to any woodland walker that there are good and poor acorn years. This is of concern because acorns are a very important wildlife food and many of our creatures feel the pinch when drought or freezes damage the crop. Birds such as jays and woodpeckers, small mammals like mice and squirrels, and even large animals such as bears and deer depend upon acorns; in fact, it has been estimated that they may constitute up to 25% of the diet of some deer come fall.

The acorn is a nut usually containing a single seed enclosed in a tough, leathery shell, and attached to a cup-shaped cap.  Acorns are important to wildlife because they are relatively large, rich in nutrients, and can be stored for later use. Percentages vary from species to species, but all acorns contain substantial amounts of protein, carbohydrates and fats, as well as calcium, phosphorous, potassium, and the vitamin niacin. It is interesting that red oak acorns are 18% to 25% fat, while white oak acorns are only 5% to 10% fat.

Acorns also contain bitter tannins, the amount varying with the species. This is particularly true of the acorns of red oaks that contain 6-10% tannin while white oak acorns have less than 2% tannin. While many insects, birds and mammals seem to metabolize tannins with few ill effects, some reportedly select acorns that contain fewer tannins, while others may store the acorns until sufficient groundwater has percolated through them to leach some of the tannins out. Still other creatures seem to get along by diluting their acorn diet with other foods.

Acorns were a traditional food of many indigenous peoples of North America. They used rock grinders to break them open, and they would soak the acorns in the streams for many days to leach the tannins. Because some species germinate in the fall, the women shelled and pulverized those acorns for immediate use, while spring-germinating types were dried in the sun to discourage mold and then cached in hollow trees or structures on poles to keep them safe from mice and squirrels.

An oak must grow for about twenty-five years before beginning to ripen a crop but then may produce about 2,000 acorns each season. Acorn production varies year to year, however, as not even the healthiest and largest oak can seem to accumulate enough food and energy to produce strong crops two years in succession. In addition, a late spring frost can damage the flowers, or drought and insect infestations can affect the crop. Curculio weevils are a major threat as they bore into immature acorns to deposit their eggs and some years, infect up to 90 percent of the acorn crop.

There are six relatively common species of oak in Wisconsin in two general groups: the red and white. The red type, including the rubrum, the Northern pin and the black oaks, have leaves with sharp-pointed, shallow lobes. Their acorns contain considerable tannin and they usually require two years to mature. The white type, that includes the alba, swamp white, and bur oaks, have leaves with rounded lobes.  Their acorns mature in one year, are not as bitter, and their shells are hairless inside. The white oak is found in well-drained woods, the swamp white oak is usually found on wet sites, and the bur oak, a large spreading, fairly slow-growing, long-lived tree typically grows in the open.  Its presence in our woodlands indicates that the area was once open grassland. It is also fire-resistant, and possesses significant drought resistance by virtue of a long taproot.

In addition to the oak, Wisconsin has hosted a number of nut trees.  American chestnuts were once common, but in 1890, the chestnut blight, which is caused by a fungus, arrived from Asia, probably spread from imported nursery plants.  Between 1904 and 1950, the disease killed or infected virtually all of the U.S. fruit-bearing American chestnuts.  Beech and butternut are now scarce but the Eastern black walnut is a common native tree with edible seeds.

Black walnut requires full sun for optimal growth and nut production and can often be found along roadsides, fields, and forest edges.  Most parts of the tree including leaves, stems, and fruit husks have a very characteristic pungent or spicy odor. The bark is deeply furrowed into thin ridges and the leaves are compound and alternately arranged on the stem.  Its nuts ripen during the autumn and have brownish-green husks and brown inner corrugated seeds.   Squirrels are important to the trees as they collect the nuts and bury those they cannot eat immediately, often allowing them to germinate and help disperse the species.

Hickories are relations of the walnuts. They're large, well-shaped trees, 60-80 feet high, and thrive best in open woods or at the edges of forests where they have plenty of light.  Hickory is appreciated as the best raw material for skis, axe handles, chair backs, barrel hoops and other wooden items that have to do hard work. The shellbark hickory (its bark comes loose in long strips) is the most popular for its nuts that are wholesome to eat with good flavor.

Although many oak trees can live 200 or more years, the champion is a certified tree in Louisiana that measures more than 37 feet in circumference with a crown spread of 150 feet, and an estimated age of more than 1,000 years! The champion black walnut is in Oregon and is almost 8 1/2 feet in diameter, 112 ft tall, with a crown spread of 144 feet.  Our oaks and walnuts are not record-holders, it is true, but some are well past the century mark and a few are magnificent specimens. We treasure them.