Prairies once covered nearly one-quarter of the Earth's land surface, making it one of the most widespread of ecosystems. However, today, only five percent of the world's grasslands remain, victims of cultivation and development.
It didn't take European settlers long to realize how fertile prairie soils were. The rich, loamy soils contained an abundance of nutrients. With the invention of the self-cleaning steel plow in 1837, the prairies' days were numbered.
Prairies represent a unique type of ecosystem that demonstrates the close relationship between components of the ecosystem and its evolution. Prairies evolved with natural disturbances such as fire. It is accurate to say that prairies exist because of disturbances. Another factor influencing the evolution of prairies is grazers or herbivores.
Herbivores Favor Grasses
Herbivores such as bison favor grasses. A unique relationship developed between fire and bison grazing. Lightning often ignited fires on prairies. After a fire, grasses germinated and grew. The succulent new grasses attracted bison.
Native Americans also used fire for habitat management and to attract bison for hunting in an early example of game management.
By grazing on grasses, growth of forbs or herbaceous plants was favored. A variety of prairie plants developed, adding color and biodiversity to prairie habitats. As long as herbivores were present, the biodiversity of prairies was maintained.
Herbivore Grazing Patterns
Bison often followed the rains, in anticipation of new grass growth. Their grazing pattern benefited grass growth and the health of prairie ecosystems. Bison graze by consuming the above-ground plants. They will move frequently, always on the lookout for new growth.
Their grazing patterns differ from cattle which will tend to uproot grasses. Cattle also follow set paths, creating bare patches of ground, subject to erosion. While bison tend to be nomadic, cattle are content to stay in the same area, eventually depleting the food resources.
Herbivores and Fires Model Prairies
The plant biodiversity of prairies depends upon the interaction of fire and grazing. In its natural state, these disturbances maintained the character and integrity of prairies.
Man nearly wiped out bison populations by the turn of the 20th century. Extinction threatened the existence of prairies without this essential management element. Modern prairie management compensates for natural disturbances through prescribed burning.
Prescribed burning is the practice of setting fires intentionally for the purposes of habitat management. Many prairie plants require the higher ground temperatures that fires create in order to germinate. Fires also remove the litter layer, allowing sunlight to penetrate to the soil level thus increasing temperatures necessary for germination.
Sources:
National Geographic.: Grassland Threats nationalgeographic.com
McClain, William E. 1989. Illinois Prairie: Past and Future: A Restoration Guide. Illinois Department of Conservation. 26pp
