Temperate Grasslands Prairies, (N. Am. [Great Plains, Palouse, California])


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Temperate Grasslands

  • Prairies, (N. Am. [Great Plains, Palouse, California])

  • Steppes (Russia - Ukraine [Hungary-Rumania])

  • Pampas (Argentina - Uruguay)

  • Veldt (S. Africa); NZ tussock grasslands


Temperate grasslands



Temperate grasslands

  • Prairies and steppes have continental climates characterised by large annual range of temperature, cool - cold winters, with most of precipitation as snow, and hot, commonly droughty summers because of high evapotranspiration rates.



North American grasslands



Palouse prairie



California grasslands



Classifying the American prairie



Mean annual temperature and precipitation in US prairies



Temperature regimes (Great Plains stations)



Precipitation regimes (west- east transect)



The prairie-forest boundary

  • Budyko suggested that the forest - grassland boundary in the midwest corresponds with a dryness ratio* of 1.1 -1.2 (=dotted line)



Pacific air mass dominance period (months of the year)



Soils

  • Loessic parent material - derived from aeolian reworking of glacial and fluvioglacial deposits in northern North America and Europe during late glacial periods.

  • Limited areas of glacial, fluvioglacial, and alluvial deposits



Soil genesis

  • In humid areas on forest margins BRUNIZEMS are the dominant soil type. Characterized by moderately acid A horizon (pH 5-6).

  • In tall-grass prairies CHERNOZEMS (MOLLISOLS) are dominant. A horizon has pH of about 6-7. Dominant processes are melanization and calcification. Rodent (esp. gopher) and insect activity may recycle >100 ton/ha/of soil per year to surface.



Chernozem/Mollisol profiles



Soil mosaic in humid prairies (humic gleys in hollows; soil erosion on ridges)



Soil catena in dry prairies



Chernozem-solonetz mosaic in grazed steppe, Rumania



Some common grass species



Grass-climate relations (highly schematic)



Topography and plant cover: mixed grass prairies (ungrazed)



Grass phenology



Cardinal temperatures for net photosynthesis, C4 and C3 plants



C4 grasses: a) less tolerant of low temperatures (e.g. flowering inhibited by night T <13°C) b) more tolerant of moisture deficits



% C4 grasses in regional grass flora



Polar and tropical source areas for prairie grasses Note: no pre-Miocene grass fossils known from plains area. Conclusion: Prairies developed in lee of rising Cordillera in mid-Tertiary.



Prairie forbs



Some N. American prairie forbs



Annual production of plant biomass in prairie grasslands note: 60-80% below-ground



Biomass (ungrazed prairie)



Grazers



Consumption: relatively small intake by shoot grazers vs. root suckers (predominantly nematodes) BUT is this a product of historical factors?



Rapid decline in grazer populations in last 200 years as a result of habitat destruction and hunting.



Buffalo grazing: Manitoba



Buffalo grazing: North Dakota





Was there a grazing sequence?



Colonization of old coyote burrows by gophers - effects of “dogtown” on neighbouring vegetation



Effects of dogtown age on local plant cover: grassland replaced by herbaceous shubland



Carnivores



Pre-Pleistocene fauna

  • Selection of prairie flora for tolerance of heavy grazing a product of radiation of diverse herbivore assemblage in Mio-Pliocene.

  • In the Pliocene the N. American plains were home to 7 genera of horses, 12 genera of antelopes; camelids, peccaries, tapirs and rhinoceroses (plus a diverse group of carnivores)

  • Think of a Nebraskan ‘Serengeti’.



Pliocene plains fauna



Fire on the prairies



The argument in favour of fire:



A prairie landscape in Illinois, showing the restriction of woodland to moister (and more fire-proof) valley bottoms



Prairie fires: Texas



Prairie fires: the Dakotas



Prairie fires: Oklahoma



Fire and prairie restoration



Fire and prairie restoration



Fire and prairie restoration



Prairies in the late Quaternary



Climatic change produces a shifting prairie - forest ecotone (cf. Hypsithermal)



Recent (and future?) climate change in the prairies (Moon Lake, ND)




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