Nature Bulletin No. 249-A December 17, 1966
Forest Preserve District of Cook County
Seymour Simon, President
Roland F. Eisenbeis, Supt. of Conservation
Approximately 50,000 years ago the earth's climate became warmer and
the last great ice sheet -- called the Wisconsin Glacier -- one lobe of
which had crept southward to cover where Chicago now stands, began
to retreat. Here and there as it melted back, huge blocks of ice were left
behind -- landlocked icebergs surrounded by moraines of gravel,
boulders, and clay or ground-up rock. When these blocks melted they
left depressions which became lakes or, in many cases, bogs. These
bogs eventually were filled with decayed and partly decayed vegetation,
or peat, and became covered with a floating mat of sphagnum or peat
moss, which supported a growth of plants now rare here -- plants typical
of the far north -- including tamarack trees.
South of the glacier there was probably a wide belt of tundra like that
near the Arctic Circle today. Beyond that, much of central and northern
Illinois was covered with a coniferous forest similar to that now found
north of Lake Superior. From the kinds of pollen grains found
preserved in peat bogs we know that, as the glacier retreated, the tundra
was invaded by advancing forests of balsam fir, then spruce, pine, birch
and maples, in that order. In the swampy areas there were tamarack,
ash, alders and willows. Finally, deciduous trees replaced the conifers,
on the higher ground and for perhaps 15,000 years our typical
oak-hickory forest, mixed with elm, ash, basswood, maples and other
hardwoods, has predominated. A few remnants of the pine stands have
persisted on poor sandy soils, and a few tamarack bogs in northern
Indiana -- notably at the south edge of the great sand dunes -- and in
Lake and McHenry counties of Illinois.
Civilization has been unkind to the tamarack bogs. Many were drained.
Others have been destroyed by fires which killed the tamaracks and the
sphagnum moss. Others are gradually disappearing because of an influx
of warm alkaline water from the surrounding slopes when cleared of
timber and placed under cultivation. Bog water is cold and acid.
Walking on such a bog is difficult and even dangerous -- something like
attempting to cross a pond covered with floating cakes of ice -- but
there one finds rare acid-loving plants such as ferns, orchids such as the
moccasin flower or lady' s slipper, the pitcher plant which traps and
consume s insects, wintergreen, cranberries, blueberries, bogrosemary,
leatherleaf, Labrador tea and many others. Among the shrubs we find
dwarf birch, winterberry, and the poison sumac which is more dreaded
than poison ivy. Perched on the spongy quaking surface mat we find
tamaracks in all stages of growth from tiny seedlings to old trees 12 or
more inches in diameter and 40 feet high. Because their network of
roots is very flat and shallow, many are blown over and lie, slowly
decaying, in a tangle upon the surface.
The Tamarack, or American Larch, also called Hackmatack, occurs to
the northern limit of tree growth in Canada, and in dwarf forms to the
Arctic Ocean. Sometimes its straight slightly tapering trunk may reach
50 or even 80 feet in height and 18 inches in diameter. The tree has a
slender spire-like shape and its stiff light-green needles, about one inch
long, are borne in compact tufts of 30 to 50 along the twigs, giving it a
distinctive feathery appearance. Unlike most cone-bearing trees, in
autumn its leaves turn lemon yellow and drop off.
Its bark contains tannin and was valued by the Indians for its medicinal
properties. The strong fibrous roots were used by them to weave into
bags, and as sewing material to make canoes. Its seeds are eaten by
In Illinois, tamaracks are relics of the Ice Age.
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Update: June 2012