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

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)