In general, grasslands occur in monsoon
Transcript of In general, grasslands occur in monsoon
Plant Ecology September 13, 2005
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Plant Ecology in a Changing World
Jim Ehleringer, University of Utahhttp://plantecology.net
Grassland and SteppeBiomes
• climate and global distribution
• North American grasslands and steppe
• mammals and grasslands
• global changes in distribution
Grassland and steppe biomes
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Grassland and steppe regions are characterized
as regions where the ratio P / PET is near 1
In general, grasslands occur in monsoon
or aseasonal (summer-wet) climate regions
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Global distribution of grassland biomes
Grasslands occupy approximately 24 % of the land surface
Grasslands by region
• prairies of North America
• pampas of South America
• velds of southern Africa
• grasslands of Sahel in northern Africa
• puszta of eastern Europe
• steppes of Russia
• grasslands of Mongolia and central Asia
• grasslands of Australia
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Steppe is a term incorporating both grasslands and
shrublands, and usually refers to high elevation sites
fire
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Grasslands of North America
• tall-grass prairie (C3 and C4)
• mixed-grass prairie (C3 and C4)
• short-grass prairie (C3 and C4)
• desert grassland (C3 and C4)
(Chihuahuan)
• California grassland (C3)
• Palouse prairie (C3)
Grassland climates
• typically continental climates
• typically hot summers and cold winters
• precipitation is generally 500 to 1,000 mm per year
• during growing season, precipitation approximately
equals evapotranspiration
• soil water typically inadequate for tree growth,
especially establishment
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Climate diagrams for grasslands
Most grasses have fibrous roots penetrating down to 1 to 2 meters depth
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Dominant life forms
• predominantly perennial grasses
• herbaceous dicots
• shrubs and trees restricted to depressions
• shrubs and trees at wetter end of the distribution (parklands)
• cool season grasses tend to be C3
• warm season grasses tend to be C4
C4 grasses predominate in warm habitats
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Grasslands of California, Washington,
and the Intermountain West are all
dominated by C3 plants
• primarily winter rain
• at present, dominated
by invasive species
• California and Washington
grasslands have largely
been converted to crops
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150 mm 300 mm 500 mm
Artemisia tridentata 14% 14% 0%
Agropyron spicatum 45% 35% 51%
Poa secunda 49% 29% 28%
Festuca idahoensis 0% 24% 38%
The relative abundances of grasses and
shrubs in the Great Basin steppe is a
function of precipitation
Creation of the steppe region
in western North America
is geologically recent Cascade
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During the Miocene, the area between British
Columbia and Utah was occupied by forests.
Uplift of Cascade Mountains created a rain
shadow with a dry region between Cascades
and Rockies.
Fire has played a role in determining the
relative abundances of shrubs versus grasses.
Shrub steppe in Utah
Atriplex Coleogyne
Juniperus Atriplex - Sarcobatus
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Burr Desert near Hanksville
Atriplex and Gutierrezia
dominate on both saline
and non-saline soils.
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Artemisia tridentata: big basin sage
Grasslands are heavily impacted by grazing.
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Thure Cerling
In arid regions, grazing
has a negative impact
on productivity.
In mesic regions, grazing has a
positive impact on productivity.
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Since 1700, grasslands, savannas, and forests
have decreased by approximately 15 %
source: Ramankutty and Foley, 1999
Grassland recovery following disturbance can be slow
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What is left of the
original grasslands
of North America?
……very little
ColoradoKansas
South Dakota
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source: Ramankutty and Foley, 1999
Agricultural modification of the land surface was
already a significant part of the landscape in 1700
Human Use of Resources
• extensive clearing of forests, approximately
8 million km2 net loss
• annual consumption of water exceeds
volume of Lake Huron
• since 1850:
- need for grain and water has tripled
- fossil-fuel use increased four-fold
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QuickTime™ and aGIF decompressor
are needed to see this picture.
Source: Ramankutty & Foley, 1999
Global Cropland Distributions
Source: Ramankutty & Foley, 1999
Global Cropland Distributions
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Source: Ramankutty & Foley, 1999
Global Cropland Distributions
Source: Ramankutty & Foley, 1999
Global Cropland Distributions
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Source: Ramankutty & Foley, 1999
Global Cropland Distributions