Differences in growth points

The main force that dictates where grasslands will dominate is the occurrence of fire. Its influence gives a distinct advantage to herbaceous plants (wildflowers or forbs) and especially grasses, over woody vegetation.

A look at the physiological differences between prairie grasses and trees explains this advantage. The main growing points for grasses are located at or below ground level. A fire that generates heat of 400° to 500° F at the surface will warm the soil only a few degrees at a depth of one inch. This leaves the growing points and roots of grasses largely undamaged. Trees and shrubs have their growing points located above ground where the heat can kill them, or at least remove years of accumulated growth. Thus, fire can limit the growth of trees and favor the growth of grasses.