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.