Few natural prairie regions in North America remain (only 1%) because most have been turned into farms or grazing land. This is because they are flat, treeless, covered with grass, and have rich soil. Conversion to agricultural land has been aided by the development of the steel plough. In the 1970s the USA deliberately reversed longstanding policy that favoured conservation practices such as fence rows, windbreaks, crop rotation and fallow land, and advised farmers to plough fence row to fence row and blanket the grasslands with wheat and corn. In Iowa, for example, less than 1 percent of the original tall-grass prairie and savannah habitat survived in 1995.
Prairie is an interlocking web of life based on hundreds of species of plants. Each serves the others; the web's fertility is self-sustaining. If farmers introduce a single species of grain, nature opposes and the monoculture must be maintained with cultivation and chemicals.