With them come fire-sensitive shrubs and woodland wildflowers. These drought and wet cycles may last 100 years or more. The easternmost portion of the prairie province has deep, rich soils and ample rainfall for luxuriant growth. This is the tallgrass prairie association. In tallgrass prairie there is, on average, less than one tree per acre.
Shrubs occur in scattered patches, especially where the soil is moist.
With less than 20 inches of rain per year, trees find it very hard to grow. Grasses and perennial forbs dominate. Extreme summer drought and bitterly cold winter temperatures are the rule, not the exception. If conditions become too rigorous during the growing season, plants go dormant to conserve their resources. When the rains return, plants resume growth with few ill effects.