TEMPERATE GRASSLANDS

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Lecture

 I.  TemperateGrasslands

A. Location

One of the most extensive of the biomes:

North America: prairies 350 million ha running from eastern deciduous forest border to western cordilleras

Eurasia: steppes 250 million ha running from Hungary to Manchuria

Argentina: pampas

Southern Africa: grassveld

Australia/New Zealand (South Island)

B. Climate

Temperate grasslands are adapted to recurring drought (50 - 120 cm rain)

emperate grasslands appear homogenous but important structural and floristic differences have developed in response to regional and local conditions (e.g. in prairie province [similar elsewhere in trends]

   increasing latitude: warm to cold and moist to dry
   east to west: moist to dry and warm to cold

C. Soil

Rich 'chernozens' or 'udolls' characterize grasslands. Possess a thick organic layer of very dark humus; active earthworm and soil fauna activity making this soil one of the most productive of terrestrial systems.

Light rainfall and high evporation makes mild leaching; therefore soil is neutral or only slightly acidic.

D. Other factors

Fire supression; once frequent and kept out woody species

Large areas destroyed by agriculture (wheat, maize, legumes): Cradle of Civilization (bread, barley, beer)

Loss of characteristic cursorial fauna: ungulates (bison, antelope, gazelle, wild horse) or equivalent flightless birds in S. America (rhea) and New Zealand (extinct moa), and rodents

E. Prairies (in more detail; but we come back to them again)

3 dominant families: Poaceae (grasses), Leguminosae (legumes), Compositae (composites)

Tall grass prairie: Andropogon gerardi (big bluestem), Panicum virgatum (switch grass), Sorghastrum nutans (Indian grass)

Tall/short grass prairie (intermediate)

Short grass prairie: Bouteloua (grama grass), Sporobolus (prairie dropseed), Agropyron (wheatgrass)

F. Evolution of grasslands

Flora of Great Plains, N. America has few endemic species suggesting that prairies developed comparatively recently and attainded present distribution only in post-glaciation (Axelrod, 1985)

Fire to some degree has been important, especially in drier times

Grazing by ungulates critical (coevolution!). Grasses and sedges have high silica content in leaves; ungulates acquired early on high-crowned teeth in which growth continually replaces the worn surfaces as adaptation; grasses and sedges have ability to resprout after grazing (good example is the prairie ungulate replacer: the lawn mower).