Transcript Temperate Grasslands

Temperate Grasslands
•
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Prairies, (N. Am. [Great Plains,
Palouse, California])
Steppes (Russia - Ukraine [HungaryRumania])
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
grasslands
Calgary
Cheyenne
Omaha
Abilene
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)
35
30
Temperature (°C)
25
20
15
Calgary
Cheyenne
Omaha
10
Chicago
Abilene
5
0
-5
-10
-15
J
F
M
A
M
J
J
A
S
O
N
D
Precipitation regimes
(west- east transect)
120
100
80
60
Cheyenn e
Omaha
Chicago
40
20
0
J
F
M
A
Chicago
M
J
J
Omaha
A
S
Cheyenn e
O
N
D
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)
9 months
<1 month
12 months
<1 month
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
mixed-grass
Melanization
Calcification
short grass
Soil mosaic
in humid
prairies
(humic
gleys in
hollows; soil
erosion on
ridges)
Soil catena in
dry prairies
1. Chernozem
1
2
2. Solonetz
3. Solod
depression
3
Na, Mg, etc
textural B;
Na+ saturation of
B and C horizons
Solonetzic solod profile
Chernozem
-solonetz
mosaic in
grazed
steppe,
Rumania
S
C
S
S
S
Some common grass species
1
2
3
4
1. Andropogon gerardii (big bluestem)
2. Bouteloua curtipendula (sideoats grama)
3. Schizachyrium scoparius (little bluestem)
4. Koeleria macrantha (?)
5. Bouteloua gracilis (blue grama)
5
Grass-climate relations
(highly schematic)
W.Wyoming
~2m tall
~1m tall
~0.5m tall
E. Illinois
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
10
% C4
grasses
in
regional
grass
flora
20
30
40
50
60
80
70
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.
C3
Agropyron, Elymus
Koeleria, Poa, Stipa
+ sedges
Bouteloua, Buchloe
Andropogon
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
1. Amorpha canescens
2. Asclepias tuberosa
3. Helenium autumnale
4. Verbena stricta
5. Aster laevis
2
3
4
5
note:
60-80% below-ground
1000 kcal m-2 a-1
Annual
production
of plant
biomass in
prairie
grasslands
Biomass
(ungrazed
prairie)
Grazers
relatively small
intake by shoot
grazers vs. root
suckers
(predominantly
nematodes)
BUT is this a
product of
historical
factors?
1000 kcal m-2 a-1
Consumption:
Rapid decline in
grazer
populations in
last 200 years
as a result of
habitat
destruction
and hunting.
Buffalo - almost extinct;
Gophers - 98% decline
1900
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 heavilygrazed land with
dense populations
of forbs.
Antilocapra americana
Colonization of old coyote burrows
by gophers - effects of “dogtown”
on neighbouring vegetation
pre-
post-
~10 m
Eastern Colorado prairies: burrow entrances shown by arrows
Effects of
dogtown age
on local plant
cover:
grassland
replaced by
herbaceous
shubland
Carnivores
(all hole ‘nesters’)
Burrowing owl
Kit fox
Badger
+ swift fox, coyote, wolf, bears
Photo credits: Greg Lasley, Bill Standley
Pre-Pleistocene fauna
• Selection of prairie flora for tolerance of
heavy grazing a product of radiation of
diverse herbivore assemblage in MioPliocene.
• 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 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)
[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)
Fire and prairie restoration
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
Fire and prairie restoration
Subdominant species richness
18
20
All plant species
Subdominant species richness
20
16
14
12
10
8
6
4
2
18
Native plant species
16
14
12
10
8
6
4
2
0
0
1996
1998
Spring burn
1996
1998
Late summer burn
1996
1998
Spring burn
1996
1998
Late summer burn
Data: Copeland et al., 2002. Restoration Ecology, 10, 31-
Fire and prairie restoration
16
Subdominant species richness
14
12
Flowering times
Late
Mid
Early
10
8
6
4
2
0
1996
Spring burn
1998
1996
1998
Late summer burn
Data: Copeland et al., 2002. Restoration Ecology, 10, 31-
Prairies in the late Quaternary
PollenViewer
Where were the “prairies” at LGM?
Most LGM pollen assemblages in southern Great
Plains have no modern analogues,
but
Neb/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
AD
Droughts
Recent (and future?) climate change in
the prairies (Moon Lake, ND)