Habitat Destruction
The three types of prairies—tallgrass, mixed grass, and short grass prairies—once covered much of central North America from the Rocky Mountains to Lake Michigan. Now, only small, often isolated fragments remain. In the east, where tallgrass was dominant, less than 1% still exists. Some states, such as Illinois and Iowa, contain only 0.1% of their original prairies. Thankfully, mixed and short grass prairies face a less dire situation with 20-25% still extant. Most of this loss came from simple destruction of the habitat as people converted prairies into other uses. For example, the tall grasses that once covered Illinois, Iowa, southern Minnesota and Wisconsin, and the eastern Great Plains fell victim to plows as farmers eagerly turned over prairie sod to get at the rich, black soil created by the deep roots of prairie plants and centuries of burning. Other prairies became cow pastures seeded with non-native grasses, roadways, or cities.

Alien Species
Like most ecosystems, prairies struggle with the problem of introduced plant and animal species competing with the native species. Some of the invading plants spread so quickly that they can cover entire fields, crowding out all other flowers and grasses.
Alien plants that pose a significant threat to prairies include the following. Invasive.org provides information on their identification and control.
   Sericea Lespedeza/Chinese bush clover
   Musk thistle
   Johnsongrass
   Purple loosestrife
   European Buckthorn
Native animals can also face stiff competition from invaders. Zebra mussels threaten to smother native mussels in prairie streams and lakes. Alien animals can do further damage by altering the landscape. Asian carp eat by tearing up aquatic vegetation. Their destructive habits stir up the muck on the bottom of rivers and ponds and turn clear waters a murky brown.
Alien animals can do further damage by altering the landscape. Asian carp eat by tearing up aquatic vegetation. Their destructive habits stir up the muck on the bottom of rivers and ponds and turn clear waters a murky brown.
 

Fire Suppression and Neglect
Intact ecosystems can largely self-regulate and protect themselves from threats through natural processes. Unfortunately, an ecosystem reduced to small, isolated remnants like the prairie has greater difficulty sustaining itself. For those ecosystems to survive, people must take an active role in managing them. For example, prairies need fires to suppress trees and burn dead vegetation so its nutrients return to the soil. When prairies covered vast, continuous expanses of land, occasional lightning strikes or hunting Native Americans set enough fires to keep trees out. Now that many prairies exist as isolated patches, natural fires almost never start and fire departments quickly extinguish those that do. Eventually, these prairies disappear, dying out underneath the light-robbing limbs of trees. Often, people do not even recognize the threat as the newly developed woodlands, filled with common "weedy" species, look just as natural to the untutored eye as a prairie full of rare and disappearing flowers.