As a result, the amount of water runoff from the prairie is small compared to land where there is no strong network of roots to absorb the rain. The roots also bind the soil tightly to the earth, protecting it against erosion. Prairie sod is so dense that settlers once used it like bricks to build houses. A square yard of soil just 4 inches deep may contain roots that would stretch for 20 miles if they were placed end to end. Grasses are the basic fabric of the prairie since they are uniquely adapted for life in the open.
Most plants grow from their tips to add length.
By contrast, grass grows from its base, emerging from a bud at, or just under the soil where the sensitive growth tissues remain protected from the elements and from grazing. Roots of some grass species extend 10-15 feet deep into the soil, and can extract moisture deep underground during dry periods. Although prairies may be grasslands in terms of sheer volume of vegetation, about three out of every four plant species found there are wildflowers. Since wildflowers, or forbs, must occupy the same space on the prairie as grasses, they have adapted ways to guarantee their share of water and sunlight. Most forbs send their roots deeper into the soil than grass roots, which allows them to tap water the grasses cannot reach.