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updated: 6/19/2013 12:28 PM

Why Prairies Developed in North America

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  • Deerfield High School Prairie Classroom

    Deerfield High School Prairie Classroom
    Jeff Hoyer

Rick Sanders, Communications Director, Lake-to-Prairie Chapter of Wild Ones

The prairie is a uniquely American biome, found nowhere else on earth outside of North America. There are many reasons that stretch out over hundreds of millions of years of geologic time and human history why this specific type of grassland developed here. Come join us for a trip through time to discover what ancient forces formed the very land we live on and the impact man has had on the landscape over the past several thousand years. Finally, we will discuss adaptations prairie plants have evolved to live here and how we too can share in the benefits they provide for our environment.

The land we now call Illinois, along with the rest of North America, was not always where it sits today on a globe. Hundreds of millions of years ago, the land we now call Illinois was actually the bottom of a shallow tropical sea. This history is important because that sea formed the bedrock of the Midwest which is the foundation of our soils. In more recent geological times, the climate of the Midwest has been heavily influenced by the series of mountain ranges bordering the western portion of North America. These mountains block most of the water that evaporates from the Pacific Ocean from falling in the Midwest. Without a steady supply of water arriving on the predominantly westerly winds, large plants like trees do not grow naturally in most of this area.

The most dramatic geological force to impact the Midwest in the past hundreds of thousand years was a series of glaciations that set up the current topography of the area and which controls where the rivers and lakes formed. The mostly flat landscape left by the glaciers created a plain where fires could sweep across the landscape for hundreds of miles untethered by mountains or valleys. Fire is the main force that kept trees from becoming established in the eastern portion of the prairie biome. Thus, native prairie plants had to adapt to living with frequent fires. The Native Americans used fire to attract big game to the tender young shoots that emerged after fires which helped to hold back trees that were encroaching from the great eastern deciduous forest. Thousands of years of prairie plants growing, compositing, and burning created the richest, thickest soils in the world. This rich soil was discovered in the late 1800's to be some of the best farm land in the world which lead to a "soil rush" that ultimately doomed much of the very ecosystem that created it.

Luckily small remnants of the great prairie ecosystem that once stretched from the Illinois to the Rockies and from Canada down to Mexico still survive in tiny postage stamp size nature preserves. With help, these small gene banks can be used to repopulate our native species before they go extinct this century leaving us with fewer options to combat serious threats like soil erosion, global warming, and shortages of freshwater. Native prairie plants not only form the soil which grows our food but also are naturally drought and pest resistant allowing them to survive under harsh condition and hold onto the soil much better than the plants used to replace them. Prairie plants sequester carbon dioxide from the air safely underground to help reduce the impacts of global warming, while their extensive root systems open up the soil to allow us to capture fresh water in our aquifers.