December 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%
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
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
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
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.