Goat prairies, sometimes termed hill prairies, or dry prairies are found mainly along the valley of the Upper Mississippi River

Upper Mississippi River

The Upper Mississippi River is the portion of the Mississippi River upstream of Cairo, Illinois, United States. From the headwaters at Lake Itasca, Minnesota, the river flows approximately 2000 kilometers to Cairo, where it is joined by the Ohio River to form the Lower Mississippi...

 in the Driftless Area, but can occur elsewhere. Normally a variant of tallgrass prairie

Tallgrass prairie

The tallgrass prairie is an ecosystem native to central North America, with fire as its primary periodic disturbance. In the past, tallgrass prairies covered a large portion of the American Midwest, just east of the Great Plains, and portions of the Canadian Prairies. They flourished in areas with...

, they are found on south-southwest-facing slopes, which receive considerable winter sun

Sun

The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

, causing a frequent freeze-thaw cycle. Bedrock generally lies not too far below. Left to themselves, they are subject to natural fire which rejuvenates the ecosystem.

Open grasslands along this stretch of the Mississippi are rapidly colonized by mixed forests. However, the low moisture content of the slopes, the winter freeze-thaw cycle, and the thin layer of soil help to keep goat prairies free of trees. Human suppression of natural fire has greatly reduced their numbers. For publicly owned goat prairies, fire has been carefully set and contained. Eastern Red-cedar

Juniperus virginiana

Juniperus virginiana is a species of juniper native to eastern North America, from southeastern Canada to the Gulf of Mexico, east of the Great Plains...

 tend to be the invading species of tree.

Sources

• "Prairie grasslands description", Minnesota Department of Natural Resources
  Minnesota Department of Natural Resources
  The Minnesota Department of Natural Resources is the agency of the U.S. state of Minnesota charged with conserving and managing the state's natural resources. The agency maintains areas such as state parks, state forests, recreational trails, and recreation areas as well as managing minerals,...
  
  , Retrieved July 23, 2007
• "Community and Landform Descriptions", The Nature Conservancy in Iowa, Retrieved July 23, 2007