Nature Bulletin No. 630   February 25, 1961
Forest Preserve District of Cook County
Daniel Ryan, President
Roberts Mann, Conservation Editor
David H. Thompson, Senior Naturalist

****:ANOTHER LOOK AT BARK

Last year, in Bulletin No. 594, we explained how a tree grows and, 
each year, adds a new layer of wood and another of inner bark. Also 
how the bark protects a tree and is as essential to its life as your skin is 
to you. Many kinds can be readily identified by their bark.

A few species are able to stretch their bark as the annual rings push it 
farther and farther outward. Even when old and large, a beech retains 
a smooth silver-gray surface free from cracks and blotches. Although 
fluted so that the trunk commonly appears "muscular", the thin bluish-
gray bark of the American hornbeam, miscalled blue beech, is equally 
smooth. In contrast, the outer bark of a sycamore has so little stretch 
that it peels off and exposes white patches of the more elastic inner 
bark.

On the trunks of most trees the bark splits and breaks or peels, always 
in a certain way, to form characteristic patterns. An elm has tight hark 
with shallow lengthwise ridges; an ash has crisscross ridges that form 
diamond-shaped patterns. A bur oak has dark, very thick, deeply 
furrowed bark. That of a white oak is pale gray with shallow fissures 
and scaly plates. The gray trunk of a hackberry is distinctively marked 
with warts and irregular ridges.

On a shagbark hickory the outer bark splits vertically into strips that 
become loose at the bottom and bend outward like shingles on an old 
cabin. On a hop hornbeam or ironwood the bark divides into narrow 
vertical strips that tend to curl at the ends until, like the red cedar, it 
has a "shredded" appearance. The silky white bark of a paper birch 
peels easily in horizontal sheets that reveal its copper-colored inner 
bark.

As stated in that earlier bulletin, the Indians used the bark of many 
trees for various purposes. The early colonists and pioneers adopted 
some of those and discovered others, such as the use of bark from a 
few kinds to supply the tannin for tanning leather. Gradually, all of 
those uses of bark from our native trees were discontinued. It became 
"useless".

However, during and since World War II, the thick shaggy bark of the 
California redwood was found to have valuable properties. It is fibrous, 
fire resistant, and durable. When shredded it is used in insulating 
materials and as a substitute for wool in fabrics; now it is being ground 
for use in floor cleaners and as a soil conditioner

From vast forests of Douglas fir in our northwestern states, huge mills 
annually convert millions of logs into lumber. Until recent years, about 
30 percent of a log was wasted in slabs and edgings with bark on 
them, usable only as fuel. Then it was discovered that Douglas fir bark 
contains valuable waxes and useful fibers. Now, debarking is part of 
the mill operation. The slabs and edgings are converted into many 
products such as toys, broom handles, and box parts. The bark is used 
as a source of wax and tannin; in cork products, plastics, adhesives, 
flooring materials, undercoatings for automobile bodies; and as a soil 
conditioner.

One of the greatest and most rapidly expanding uses of timber today is 
to supply pulpwood for the manufacture of several hundred different 
kinds of paper, cardboard, carton materials, insulation boards, and 
many other products. All wood to be converted into pulp must be free 
from bark. Bark not only makes the pulp and paper dirty, it adds 
useless bulk because it contributes nothing to the strength or finish of 
the paper. Expensive machines and processes are now used to debark 
pulpwood logs at the mills or as they are cut in the forests.

Someday we will find uses for all bark.