Forest ecoregions of the Eastern United States.
Source: R.G. Bailey [Ecoregions of the United States, USDA Forest Service (scale 1:7,500,000, revised 1994)]

A wedge of prairie (251 on the map) stretches from eastern Kansas and Oklahoma across central Illinois and into Indiana. This region is called the Prairie Peninsula.

Characteristics of the Eastern Broadleaf Forest
Tall, broadleaf, deciduous trees dominate the Eastern Broadleaf Forest. In Illinois, oak and hickory dominate a majority of the forests. 

These forests typically have a dense canopy during the summer months. In the spring, before the trees leaf out, the groundcover is dominated by spring ephemerals (plants that bloom for a very short time), such as trout lily and other flowering herbs.These plants are shaded out as the summer canopy develops. 

Climate
Winters in this region are cold, but not as harsh as in the boreal forest region to the north. Within Illinois, the northern forests experience a slightly colder, longer winter and cooler summer than the southern Illinois forests, so the dominant vegetation differs between northern and southern forests. 

Overall, summers are warmer than in boreal forest regions to the north, and the longer growing season and precipitation support deciduous forests or mixed evergreen/deciduous forests. 

Evergreen forests
Evergreen forests are present in the northern and southern regions of Illinois. Needle-leaved trees (conifers) dominate these forests.

For further information, read Evergreens.

White Spruce (Picea glauca)