Nature Bulletin No. 249-A   December 17, 1966
Forest Preserve District of Cook County
Seymour Simon, President
Roland F. Eisenbeis, Supt. of Conservation

****:TAMARACK BOGS

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 
many birds.

In Illinois, tamaracks are relics of the Ice Age.