July 16, 2010

Evergreens That Aren't

by Susan L Post

All "evergreen" (coniferous) trees in Illinois are not always green. Two unique species, the bald cypress and tamarack, actually lose their leaves each fall and contribute to Illinois' fall color display.

As curious as it may seem, two species of evergreen trees that occur naturally in Illinois actually lose their leaves each fall, much like an oak or maple. Both inhabit unique wetlands. One species, the bald cypress, occurs naturally only in the swampy lowlands of far southern Illinois, while the other, the American larch or tamarack, is a denizen of the bogs of far northern Illinois.

The name Bald Cypress comes from the tree's habit of shedding its needles, giving it a bald appearance. These swamp trees have swollen bases and knees and can reach giant proportions. The cypresses swollen base develops in response to water and helps provide a firm footing in the swamp. Knees are distinguished by their smooth, conical shape, and are produced on land that is subject to alternate flooding and drying. The height of a cypress knee usually corresponds to the high-water mark in the swamp. The largest tree in Illinois is a Bald Cypress along the Cache River; many of the immense trees along this sluggish southern Illinois stream are 800-1500 years old. The original extent of cypress swamps in southern Illinois was about 250,000 acres, but today can be seen in preserves such as Heron Pond-Little Black Slough in Johnson County and Horseshoe Lake in Alexander County.

At the other end of Illinois, a few scattered bogs can be found in northern Lake and McHenry counties, the only remaining examples of a plant community common in most northeastern states. Illinois bogs are acidic wetlands that contain very typical plants such as sphagnum moss, carnivorous plants, wild orchids, and the tamarack. Tamaracks grow on spongy hummocks in the bog and are generally rather short and scrubby. These attractive trees can grow elsewhere, but are commonly found in bogs because they can tolerate the extremely acidic water of the bog, something other trees cannot do. In addition, tamaracks are not very good competitors in a forest habitat, thus they are largely confined to bogs. The best place to see tamaracks in a classic bog in Illinois is Volo Bog State Natural Area in Lake County.

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