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

prairies, steppes, pampas, veldt…..

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 grassland

s

Abilene

Calgary

CheyenneOmaha

Chicago

Palouse prairie

eastern Washington, and Oregon, Idaho

California grasslands

Classifying the

American prairie

above: Carpenter, 1940.

below: Clements and Weaver, 1939.

Mean annual temperature and precipitation in US prairies

Temperature regimes(Great Plains stations)

-15

-10

-5

0

5

10

15

20

25

30

35

J F M A M J J A S O N D

Calgary

Cheyenne

Omaha

Chicago

Abilene

Tem

pera

ture

(°C

)

Precipitation regimes(west- east transect)

J F M A M JJ A S O

N D

Cheyenne

Omaha

Chicago

0

20

40

60

80

100

120

Cheyenne

Omaha

Chicago

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)

Budyko dryness ratio values, N. America

Hare (1980) Atmos.-Ocean 18, 127-153.

Pacific air mass dominance period (months of the year)

12 months

<1 month

<1 month

9 months

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

Melanization

Calcification

mixed-grass short grass

Soil mosaic in

humid prairies (humic gleys in hollows;

soil erosion on

ridges)

Soil catena in dry prairies

12

3

Solonetzic solod profile

2. Solonetz3. Solod

textural B; Na+ saturation of B and C horizons

1. Chernozem

depression

Na, Mg, etc

Chernozem-

solonetz mosaic in grazed steppe,

Rumania SS

S

S

C

Some common grass species

1. Andropogon gerardii (big bluestem)2. Bouteloua curtipendula (sideoats grama)3. Schizachyrium scoparius (little bluestem)4. Koeleria macrantha (?)5. Bouteloua gracilis (blue grama)

1 2 3 4

5

Grass-climate relations(highly schematic)

~2m tall

~1m tall

~0.5m tall

E. IllinoisW.Wyoming

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

% C4grasses

in regional grass flora 80 70

60

50

40

30

20

10

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.

C3Agropyron, ElymusKoeleria, Poa, Stipa

+ sedges

Bouteloua, BuchloeAndropogon

C4

Prairie forbs• Streletsk reports 180 spp of flowering

plants from the Ukrainian steppes (only 20 of which are grasses).

• In the tall-grass prairies of North America >70 spp may be in flower at once.

• Forbs have variable drought tolerances and phenologies.

• Flowering times range from March (e.g. Tulipa/Hyacintha in steppes) - Sept/Oct (e.g. Delphinium spp.).

Some N. American prairie forbs

1 2 3

4 5

1. Amorpha canescens2. Asclepias tuberosa3. Helenium autumnale4. Verbena stricta 5. Aster laevis

Annual production

of plant biomass in

prairie grasslands

note: 60-80% below-

ground

100

0 k

cal m

-2 a

-1

Biomass(ungrazed

prairie)

Grazers

Consumption:

relatively small intake by shoot grazers vs. root

suckers(predominantly

nematodes)BUT is this a product of historical factors?

100

0 k

cal m

-2 a

-1

Rapid decline in grazer

populations in last 200 years as a result of

habitat destruction

and hunting.

1900Buffalo - almost extinct;Gophers - 98% decline

Buffalo grazing: Manitoba

“In vallies and humid situations, the grass grows to a great height, which fattens our horses in a short time, but the buffalo usually makes choice of the hilly, dry ground to feed on, the blades of grass on which are small, short and tender. When a numerous herd of these animals stay any length of time in one place, the ground is absolutely barren there for the remainder of the season…”

Umfreville (1790)

Buffalo grazing: North Dakota

“This afternoon I rode a few miles up Park river. The few spots of wood along it have been ravaged by buffaloes; none but the large trees are standing . . . The small wood and brush are entirely destroyed, and even the grass is not permitted to grow. The bare ground is more trampled by these cattle than the gate of a farmyard . . .”

Alexander Henry (1801)

Was there a grazing sequence?

Antelope reported to follow buffalo; they appear to prefer heavily-grazed land with dense populations of forbs.Antilocapra americana

Colonization of old coyote burrows by gophers - effects of

“dogtown” on neighbouring vegetation

Eastern Colorado prairies: burrow entrances shown by arrows

~10 mpre- post-

Effects of dogtown

age on local plant cover: grassland

replaced by herbaceous shubland

Carnivores

Burrowing owl Kit fox Badger

Photo credits: Greg Lasley, Bill Standley

(all hole ‘nesters’)

+ swift fox, coyote, wolf, bears

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

Are the tall-grass prairies a climatic climax, or is fire the predominant generative and maintaining factor?

The argument in favour of fire:

“I grew up in the timbered upland peninsula formed by the junction of the Missouri and Mississippi Rivers. The prairie began a few miles to the north and extended far into Iowa. The broad rolling uplands were prairie, whatever their age and origin, the stream-cut slopes were timbered….. From grandparents I heard of the early days when people dared not build their houses beyond the shelter of the wooded slopes, until the plough stopped the autumnal prairie fires. In later field work in Illinois, in the Ozarks, in Kentucky, I met parallel conditions of vegetation limits coincident with breaks in relief. I gave up the search for climatic explanation of the humid prairies.”

Carl Sauer, 1969. Agricultural Origins and Dispersals.

A prairie landscape in Illinois,showing the restriction of woodland

to moister (and more fire-proof) valley bottoms

Prairie fires: Texas“the Indians of the interior have another intolerable method, . . . which is to fire the plains and forests . . . both to drive the mosquitoes away and at the same time drive lizards and like things from the earth to eat. They also kill deer by encircling fires; deprived of pasturage, the animals are forced to seek it where the Indians may trap them”.

Cabeza de Vaca, A.N. Relación (1542)Shipwrecked by a hurricane on the coast of Texas with his crew in 1527; Cabeza de Vaca lived with the Indians in Texas from 1528-1535.

Prairie fires: the Dakotas

“the Plains are on fire in view of the fort on both sides of the river, it is said to be common for the Indians to burn the Plains near their Villages every Spring for the benefit of their horses and to induce the Buffalow to come near them”.

Lewis and Clark’s Journals - describing their winter quarters in North Dakota in 1805.

Prairie fires: Oklahoma

[Oct. 24, 1849] “ yesterday we could see the smoke of the Prairie burning in every direction but today it got close to us. It was the work of the Osages”

Woodhouse, S.W. Journals (1992)

[Oct 31, 1832] “It was the time when hunting parties of Indians set fire to the prairies; the herbage . . . was in that parched state, favorable to combustion . . .”

Irving, W.A. A Tour on the Prairies (1835)

Fire season

Spring Late-summer

Flame height (L, m) 1.9±0.4 0.7±0.1

Intensity (I; kW/m)1 1260±520 120±20

Litter consumption (%)

100 91±2

II= 259.83L2.174

Data: Copeland et al., 2002. Restoration Ecology, 10,31-323

Fire and prairie restoration

Fire and prairie restoration

Data: Copeland et al., 2002. Restoration Ecology, 10, 31-323

0

2

4

6

8

10

12

14

16

18

20

1996 1998 1996 1998

Spring burn Late summer burn

Subdominant species richness

Native plant species

0

2

4

6

8

10

12

14

16

18

20

1996 1998 1996 1998

Spring burn Late summer burn

Subdominant species richness

All plant species

Fire and prairie restoration

Data: Copeland et al., 2002. Restoration Ecology, 10, 31-323

0

2

4

6

8

10

12

14

16

1996 1998 1996 1998Spring burn Late summer burn

Subdominant species richness

Late

Mid

Early

Flowering times

Prairies in the late QuaternaryPollenViewer

Where were the “prairies” at LGM?Most LGM pollen assemblages in southern Great Plains have no modern analogues,

butNeb/Kansas ~ open subalpine forest/parkland?

C.Texas ~ sagebrush steppe?northern Mexico-NM ~ juniper/pinyon woodland?

*see “Poaceae” and “prairie forbs”

Climatic change

produces a shifting prairie - forest

ecotone

(cf. Hypsithermal)

500 km

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

AD

Dro

ug

hts

Wets