Lake County Habitats

The use of rivers by living things is largely controlled by physical and chemical factors. Physical factors include the size of the river and the amount of water flowing through it, the consistency of the flow, the speed of the current, and the nature of the bottom. Chemical factors in our region are mostly about the extent of pollution.

Biologists have divided the rivers of the Chicago region into four size categories. The smallest of these is the headwater stream, a tiny creek that may flow only intermittently. Low order streams are small- to medium-sized creeks whose bottoms have been shaped by the water to produce riffles and pools, alternating sections of fast shallow water and slow deep water. Mid-order streams are our most complex river habitat. Water flows through both deep and shallow pools. Floodplains begin to develop along streams of this size. Our largest rivers, such as the Des Plaines, have broad floodplains. Floodplains are low lands adjoining the river channel that are regularly flooded during periods of heavy flow, such as early spring. The flooding exerts a heavy influence on vegetation along the banks of large rivers.

Prairies are grasslands. The dominant plants are grasses—although many other kinds of plants are present. Most of the biomass, the living material, of prairie grasses and wildflowers—is underground. On deep soils, the root systems of some prairie species extend nearly 20 feet below the surface. They may live for decades, each spring sending up new green shoots to flower, set seeds and die.

Grasslands develop on flat lands in areas where long periods without rainfall are common—like summer droughts of the American Midwest. Periodic droughts and the flat ground that offers few obstacles to advancing flames have made fire a major force in the ecology of the world's grasslands. Millions of years of evolution in the presence of fire have made the tallgrass prairie dependent on periodic fires for its survival. Without fire, prairies are invaded by trees and shrubs that kill the prairie plants with their shade. In the presence of fire, prairies are very stable communities.

During the past 175 years, millions of acres of tallgrass prairies have been converted to cornfields or covered with building. The tallgrass prairie survives in tiny fragments. Hope for the survival of this ecosystem rests on good management of these fragments and on restoration projects that return prairie to lands where it has not grown for a century or more.

Lakes are bodies of water large enough to have at least one wind-swept beach. When winds are high, they blow across the water and create waves large enough to wash away any plants attempting to colonize the beach. Lakes and ponds can be divided into categories based on abundance of nutrients and how these nutrients are cycled through them.

Our inland lakes are generally of moderate depth. One in Lake County, reaches a depth of 50 feet and has been named Deep Lake. Thirty to 35 feet is a more usual depth.

Lakes are ecologically complex communities with several distinctive kinds of organisms living in them. Healthy lake communities have animals at different trophic—that is, feeding—levels, from herbivores to top carnivores. Fish-eating birds such as cormorants and terns enter the picture as predators.

Lake Michigan
The Great Lakes are among the wonders of the world. The five inland seas hold one-sixth of the world’s surface fresh water. Lake Michigan is the third largest of the lakes with a surface area of 22,300 square miles.

This young landscape, combined with the many layers of varied deposits left by the glaciers and by post-glacial lakes, produces one of the most diverse collections of wetlands in North America. Some wetlands are submerged year round. Others are wet in spring and early summer and dry by August. In some wetlands, water can be hip-deep. In others, the soil is saturated but little or no water stands above the surface. These differences exert a powerful influence on the vegetation of a wetland. The vegetation, in turn, exerts a major influence on what animals live there.

Lake, shrub swamp, floodplain, river marsh, sedge meadow, fen and bog are all types of wetlands that are distributed across the Lake County landscape.

The Chicago region has one of the most diverse collections of wetlands in North America. The regional community-classification system recognizes six major categories of wetlands: marsh, bog, fen, sedge meadow, panne and seeps and springs. In addition, wet prairie is often considered a wetland type. All wetlands are inundated or saturated by surface or groundwater for a sufficient part of the year to support vegetation that is adapted to life in saturated soil. The vegetation, the amount of water they hold and the chemistry of their soil and water define the different wetland types.

The classifications scientists use to describe natural communities give a short, simple name to a very complicated thing. When we talk of "oak savannas" or "oak-hickory forests," we are referring to communities that may include hundreds of species of plants, and—when you add up all the beetles, spiders, snails, and centipedes—thousands of species of animals. When we study a natural area and decide what communities are present, we lok at the entire biota, all the living things. Overall differences in the biota tell ecologists whether a given community developed as an open woodland or a dense forest. The biota also help us identify communities that have been seriously harmed by the changes that large scale settlement has brought.

All of our wooded communities have been changed by the altered conditions that have followed settlement. The suppression of fire, in particular, has had a profound effect. With fire gone from the community, fire sensitive trees have moved into oak forest, open woodlands and savannas, casting dense shade and alterning our wooded communities. Fortunately, restoration can reverse this trend.

The forested community class includes all the community types that are dominated by trees, with an average canopy cover of greater than 50%. Forest communities have a multi-layered structure composed of the canopy, sub-canopy, shrub, and herbaceous layers. Historically, this multi-layered structure was maintained through fires and other natural disturbances. Within the forest community class there are four community types: upland forest, floodplain forest, flatwoods, and woodlands. Woodlands developed under a canopy cover of 50-80%, intermediate between that of savanna and forest.

We are a member of Chicago Wilderness, a regional alliance that connects people and nature. The Atlas of Biodiversity is a richly illustrated introduction to the endangered natural communities of the Chicago Wilderness region, including descriptions of tehse endangered communities, how they sustain themsleves through ecological processes, and how natural forces—and people—have shaped them over thousands of years.