Included here is the extensive grassy plains east of the Rocky Mountains. Its boundary extends north to the coniferous forests of Alberta, Saskatchewan and Manitoba, east to the deciduous forests of the Appalachian zone and south and southwest to the Sonoran deserts.

North American Prairie Grassland

These grasslands can be roughly divided into tall grass prairie in the east, short grass prairie in the west and mixed grass prairie between the two. This reflects increasing aridity from east to west. For thousands and possibly millions of years, fire has been an important natural factor. Consequently many of the plant species are adapted to tolerate fire. In fact, tall grass prairie tends to be replaced by forest when protected from fire. Also prior to man’s intervention, prairie provided grazing for literally millions of buffalo and other grazing animals.  Tall-grass prairie is largely composed of bunchgrass and sod forming grasses. The dominant species are Andropogon gerardii, Panicum virgatum, Schizachyrium scoparium and Sorghastrium nutans. Before man’s interference tall-grass prairie formed a dense cover commonly reaching heights of up to 3 m, but most of the canopy today is less than 1 m. In short-grass prairie Bouteloua gracilis and Buchloe dactyloides are the dominant sod forming species, while other important grasses are Agropyron smithii, Hilaria jamesii, Koeleria cristata, Muhlenbergia torreyi, Sporobolus crytandus and Stipa comata. These short-grass prairies are thought to be more of a true climax community than tall-grass prairies, and many of the species are draught resistant. The dryness of this habitat was shown in the 1930s when the so-called ‘dust bowls’ were created as a result of trying to plow short-grass prairie. Mixed-grass prairie is a blend of tall and short grass prairie species, and in fact, represents a large ecotone between this two prairie types. Typical dominants are species of Agropyron, Bouteloua, Colamovilfa, Schizachrium, Sporobolus and Stipa.

Although grasses dominate the prairies and characterize the landscape there are also large numbers of other, often colourful, flowering plants from other families. The Asteraceae are particularly prominent with different taxa characterizing each of the seasons - Gaillardia and Senecio in spring, Helianthus, Ratibida, Rudbeckia and Silphium in midsummer and Aster and Solidago in the fall. Most of the endemic species are also forbs such as Amorpha nana (Fabaceae), Astragalus barrii, A. gracilis, A. hyalinus, A. pectinatus, A. plattensis (Asteraceae), Lespedeza leptostachya (Fabaceae), Psoralea cuspidata, P. hypogaea, P. linearifolia (Fabaceae), Carex hookerana (Cyperaceae), Daucosma laciniatum, Eryngium leavenworthii, Eurytaenia texana (Apiaceae), Eriogonum correllii, E. vischeri (Polygonaceae), Haplopappus engelmannii (Asteraceae), Lesquerella angustifolia, L. arenosa, L. auriculata, L. calcicola, L. engelmannii, L. ovalifolia, L. recurvata, L. sessilis (Brassicaceae), Oenothera fremontii (Onagraceae), Phlox andicola, P. oklahomensis (Polemoniaceae), Tomanthera densiflora (Scrophulariaceae), Valeriana texana (Valerianaceae) and the moss Aschisma kansanum (Pottiaceae).

The prairies are not completely treeless - Populus deltoides var. occidentalis (Great Plains Cottonwood) and sometimes other species form gallery forests along many of the large streams, and dwarf stands of Quercus macrocarpa var. depressa occur in some of the wetter areas. Also Pinus ponderosa, Picea glauca and other species can be found in the Black Hills, but these represent a dome-like outlier of western American cordillera.

A type of prairie also extends on to Edwards Plateau in south central Texas where grass taxa such as Andropogon, Bouteloua and Buchloe can be found. However it also shares a number of species with the Chihauhuan and Tamarlipan deserts and as such represents a transition zone to the Sonoran BioProvince. Nevertheless, the area is important in its own right and supports a number of endemic species such as Anemone edwardensis (Ranunculaceae), Quercus texana (Fagaceae), Streptanthus bracteatus (Brassicaeae), Styrax platanifolia, S. tenax (Styracaceae), Lythrum ovatum (Lythraceae), Galium correllii (Rubiaceae), Matelea edwardsensis (Asclepiadaceae), Forestiera reticulata (Oleaceae), Physostegia correllii (Lamiaceae), Buddleja racemosa (Loganiaceae), Campanula reverchonii (Campanulaceae), Erigeron mimegletes (Astereaceae), Verbesina lindheimeri (Asteraceae), Dasylirion heteracanthium (Nolinaceae), Yucca rupicola (Liliaceae) and Tridens buckleyanus (Poaceae).


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