Prairie consists of tall grasses comprising the dominant herbs, and subdominant forbs (broad-leaved herbs). Trees and shrubs are almost totally absent but may occur in the same region as forest or woodland patches~ in valleys and other topographic depressions. The grasses are deeply rooted and form a continuous and dense sward. The grasses flower in spring and early summer; the forbs in late summer. In Iowa, a representative region of tall-grass prairie, typical grasses are big bluestem.
The tall-grass prairies are typically associated with continental, middle-latitude climates described as sub humid, that is in which evapotranspiration and precipitation are almost balanced on an average yearly basis and range between 20 and 40 in (50-100 cm). In summers air and soil temperatures are high, so that on uplands soil moisture is not adequate for tree growth and deeper water sources are beyond reach of tree roots. The North America Prairies are found in a broad belt extending from Illinois, northwest-ward to southern Alberta and Saskatchewan. On the world map of vegetation the North American prairie includes the eastern and northern parts of Class 0. Areas of forest are mixed with areas of prairies in a transitional belt between forest and prairie regions.
Because the tall-grass prairies grade into short grass prairies and eventually into steppe grasslands in the direction of increasing aridity, it is not practical to try to list all world regions of tall-grass prairies. In Europe, a typical region of tall-grass prairie is the puszta of Hungary. The Argentina's pampa is often cited as a region of prairie vegetation, as are areas in north China.
The pedogenic process associated with prairie vegetation is calcification and results in development of prairie and chernozem soil profiles.
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