Black prairie soils cover the northern sections of the formerly glaciated sections of Illinois. The deep, fertile prairie soils, enriched over thousands of years by humus derived from grasses and other organic matter that once covered them, are today among the most productive soils in the world. However, many miles of underground drains and open ditches must be maintained in the flatter sections in order to drain the land. Farther south, lighter-colored and less fertile soils, called planosols, predominate. They are characterized by a hardpan, or impervious layer, just below the surface, which prevents proper drainage of the cropland. The yield per acre of crops grown on the planosols is generally lower than on the prairie soils. Gray-brown alfisols cover the hilly areas in the western sections of the state. In most cases they are highly acidic and unsuited for crops. The hilly and unglaciated southern tip of Illinois is covered with thin, gray alfisols, which are lacking in the organic matter and mineral elements necessary for producing good crops. Fertile mollisols are found along the valleys of the Ohio, Mississippi, and Illinois rivers. Fine silts, which are extremely productive when properly drained, occur along the margin of Lake Michigan.
Little more than 200 years ago, when nearly all of Illinois was still unsettled, forests covered the southern third of the area and tall grasses and prairie flowers covered most of the northern and central sections. These great stretches of prairie included prairie cordgrass, big bluestem, little bluestem, and switch grass. In many damp areas the grasses grew profusely, sometimes higher than a person on horseback. In early summer wildflowers on the prairie formed a sea of color that stretched away into the distance farther than the eye could see. These great grassland areas were broken only by tongues of woodland along the rivers and scattered upland groves. Today most of the original vegetation of Illinois has been cleared for farming or otherwise modified by human activity. However, the term prairie, originally a French word meaning “meadow,” has been retained to describe the former grassland regions of Illinois and other Midwestern states.
Forests and woodlands now cover only 13 percent of Illinois. The chief deciduous trees found in the southern part of the state include white oak, which is the state tree, shingle oak, post oak, sweet gum, river birch, and maple. Other trees common to Illinois include black walnut, honey locust, black cherry, basswood, cottonwood, Kentucky coffee, hackberry, hickory, ash, and sycamore. Illinois has few conifers, but there is a notable stand of white pine in White Pines Forest State Park, near Rockford. Other coniferous species, found mostly in northern Illinois, include red cedar and juniper.
The violet, which is the state flower of Illinois, grows wild throughout the state. Other wildflowers that still grow in profusion in undisturbed woodlands and roadside areas include Dutchman’s-breeches, blue phlox, black-eyed Susans, goldenrods, dogtooth violets, bluebells, trilliums, buttercups, bloodroots, prairie docks, toothworts, blazing stars, and asters. "Illinois" © Emmanuel BUCHOT, Encarta, Wikipedia
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