Illinois Climate

Tree Distributions – Post-Glacial

Mean Monthly Temperatures – Urbana, Illinois

Illinois Climate Basics – mean from Mean annual temperature ranges from 47 F in the north to 59 F in the south. The mean January temperature ranges from 22 F in the north to 36 F in the south. The mean July temperature ranges from 73 F in the north to 80 F in the south. The average length of the growing season ranges from less than 160 days in the northwestern corner of the state to more than 200 days in the southern tip of the state. Average annual precipitation increases from about 32 inches (81 cm) in the north to 47 inches (119 cm) in the south.

Illinois Climate

Climate Migration

Typical Driftless Region Topography

Wisconsin Driftless Region Part of an area extending from nw Illinois into Wisconsin, Iowa and Minnesota that apparently escaped Pleistocene glaciation. Characterized by rugged terrain that was once mostly forested. Has coldest climate in state. Contains several distinctive plants of northern affinity and some species represent relicts of pre-ice-age flora.

Wisconsin Driftless Region Plant communities – upland forests of black oak, white oak, sugar maple, basswood, and red oak. Flood plains – silver maple, American elm, green ash. Cliffs and cool shaded glens have white pine, Canada yew, and white birch. Prairies – dry – plains buttercup, pasque flower, june grass and wilcox’s panic grass, little bluestem (the dominant) and side-oats grama.

Jeweled shooting star – Wisconsin Driftless Region

Woodland white violet – Wisconsin Driftless Region

Rock River Hills

Region of rolling topography that is drained by the Rock River. Has thin mantle of glacial till. Prairie formerly occupied extensive areas of level uplands, but forest was abundant along rivers and streams and in dissected uplands.

Rock River Hills Forests – similar to Wisconsin Driftless division with addition of bur oak and wild black cherry on dry uplands, and slippery elm on wet uplands. Floodplain forests have silver maple, black willow, cottonwood, American elm, and ashes Prairies – similar to those in the Grand Prairie – dry prairies dominated by big bluestem, indian grass, and prairie dropseed. Wet prairies had prairie cordgrass, bluejoint grass,and big bluestem. Marshes – dominated by cattails, bulrushes, sedges and common reed.

Prairie Dropseed – Rock River Hill Country

Yellow Birch – Rock River Hill Country

Lake in the Hills Fen - Illinois

Northeastern Morainal Division Most recently glaciated region of Illinois. Glacial landforms are common and responsible for rough topography of the region. Lake bed deposits and beach sands are frequent features. Soils derived from glacial drift rather than loess. Drainage is poor and many natural lakes are found. Contains distinctive northern and eastern floral elements and bog elements too.

Northeastern Morainal Division Plants – dry uplands dominated by bur oak and white oak. Mesic uplands dominated by sugar maple, red oak, basswood, and white ash. Many shrubs – highbush cranberry, red elder. Beech in a few ravines along Lake Michigan. Floodplain forests – silver maple, American elm, and green ash. May also have swamp white oak. Black oak and hill’s oak on sandy soils. Jack pine and white pine on sandy ridges. Tamarack in poorly drained depressions. Prairie – this area was about 60% prairie. Dry prairie – little bluestem and sideoats grama. Mesic and wet prairie – big bluestem, indian grass, prairie dropseed, switchgrass, bluejoint grass, prairie cordgrass, and many forbs. Sand prairies had fringed orchids, gentians, and lupine.

Northeastern Morainal Division Fens – wet prairie with alkaline water source – notable plants white lady’s slipper, grass of parnassus, meadow spikemoss, Ohio goldenrod, white camas Marsh – cattails and bulrushes Sedge meadow- sedges, dogwoods, willows, and speckled alder Bog – true bogs found in Illinois only found in this division. Poorly drained depressions. Unique plants – pitcher plants, sundews, cranberry, leatherleaf, poison sumac, winterberry, and dwarf birch

Pitcher Plants – Northeastern Moraine

Volo Bog - Illinois

Nachusa Grasslands

Grand Prairie Division A vast plain primarily occupied by tallgrass prairie. Soils were developed from recently deposited loess, lake bed sediments, and outwash and are generally very fertile. Natural drainage was poor resulting in many marshes and potholes. Forests bordered the rivers. Bison and waterfowl were once very common here.

Grand Prairie Division Prairie – contained several hundred species of grasses and forbs – big bluestem, indian grass, prairie dropseed, switchgrass, little bluestem, leadplant, compass plant, prairie dock, rattlesnake master. Wet sites dominated by prairie cordgrass, sedges, bluejoint grass, ironweed, boneset, swamp milkweed, water hemlock. Sand prairies – little bluestem, fall witchgrass, and sand dropseed. Also have species more typical of the Great Plains – western ragweed, prickly-pear, poppy mallow, hairy grama, western sunflower, silky aster

Grand Prairie Division Forest – generally found along stream valleys and moraines. Dry sites – white oak, black oak, and shagbark hickory – often with shingle oak and bur oak too. Wet sites – sugar maple, slippery elm, American elm, hackberry, red oak, white ash, black walnut, bitternut hickory, and bigtooth aspen. Floodplains – silver maple, American elm, ash. Marshes – bulrushes, sedges, cattails, bur-reeds, common reed, arrowhead, pickerelweed, beggar-ticks.

Leadplant - Grand Prairie

Illinois Grand Prairie

Illinois and Mississippi River Bottomlands Encompasses the rivers and floodplains of the Mississippi River above the confluence with the Missouri River and the bottomlands and backwater lakes of the Illinois River south of La Salle. Most was originally forested, but some prairie and marsh existed too.

Illinois and Mississippi River Bottomlands Forests- bottomlands dominated by silver maple, American elm, and green ash. Also pin oak, pecan, bur oak, sycamore, honey locust, hickories, and black walnut. Black willow and river birch common along Mississippi River. Prairie – some mesic and wet prairie similar to those in Grand Prairie. Marsh – cattails, bulrushes, sedges, and bur-reed Spring bogs – spring fed bogs in peat terraces are found along the Illinois River – unique to it – distinctive plants – skunk cabbage, black ash, poison sumac, and willows

Illinois and Mississippi River Bottomlands

Illinois and Mississippi River Bottomland Forest

Skunk cabbage – Upper Mississippi River and Illinois River Bottomlands

Bottomland Topography

Sand Prairie Habitat

Illinois River and Mississippi River Sand Areas Sand areas and dunes in the bottomland areas of the two rivers and perched sand dunes atop bluffs in Jo Daviess County. Scrub oak forest and dry sand prairie are the natural plant communities here. Many of the plant species are more typical of western prairies and relict western amphibian and reptiles are found here.

Illinois River and Mississippi River Sand Areas Forest – scrubby black oak along Mississippi and scrubby black oak and blackjack oak along the Illinois Sand prairie – major plant community – composed of little bluestem, june grass, Indian grass, and porcupine grass – also prickly pear, hairy grama, goat’s rue, spotted monarda, three-awn grass, sand love grass

Hairy Grama Grass – Illinois River and Mississippi R. Sand Areas

Blackjack oak - Illinois River and Mississippi R. Sand Areas

Western Forest Prairie Division

Strongly dissected glacial till plain from Illinoian and Kansan glaciations. Forest was dominant vegetation but prairies were extensive on the level uplands. Prairie soils are derived from loess and are very fertile.

Western Forest Prairie Division Forests – uplands are oak-hickory association of black oak, white oak, and several species of hickory. Fine-textured soils support post oak and blackjack oak. Mesic forests contain white oak, red oak, basswood, sugar maple, and slippery elm. Floodplain forests have silver maple, American elm, ashes, and box elder.

Western Forest Prairie Division Prairies – Very similar to those in the Grand Prairie though most was dry to mesic prairie with little wet prairie. Marsh – not as common as in Grand Prairie but similar in species composition.

White Oak - Western Forest Prairie Division

Mississippi River Bluffs – Middle Mississippi Division

Middle Mississippi Division This is a relatively narrow band of river bluffs and rugged terrain bordering the Mississippi River from Rock Island County to St. Clair County and the lower Illinois River floodplain. Forest is predominant natural vegetation but hill prairies are common on west-facing bluffs. Soils generally developed from very deep loess. Limestone cliffs are also common.

Middle Mississippi Division Forest – mostly mesic and dry forests associated with dissected uplands – dry are dominated by black oak and white oak; mesic by sugar maple, basswood, red oak, hackberry, slippery elm, black walnut. Floodplain forests – silver maple, hickories, cottonwoods, sycamore. Post oak is common on heavy soils and near ridge tops. Prairie – dominated by little bluestem, side-oats grama, purple prairie clover, flowering spurge. Common western plants include scurf pea and stickleaf.

Basswood - Middle Mississippi Division

Purple Prairie Clover – Middle Mississippi Division