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Illinois Plant Communities –
Prairie Ecosystems
Illinois Native Ecosystems Today
• 2,352 high quality acres of remnant tallgrass
prairie (less than 1/100 of 1% of the original)
• 918,000 acres of wetland (only 6,000 of high
quality)
• 4.26 million acres of forest – but most of the forest
is second growth that has developed since the
1940’s – only about 11,600 acres original old
growth forest remains in Illinois
Grasslands
• Grasslands are biological communities and
ecosystems containing very few trees or
shrubs, characterized by herbaceous
vegetation and dominated by grasses,
family Poaceae
Grasslands Around the World
Types of Grassland
Grassland Type
Area (km2 x 106)
High grass savanna
7.25
Tallgrass savanna
10.10
Tallgrass prairie
4.09
Shortgrass prairie
3.11
Desert grass savanna
5.96
Mountain grassland
2.05
The Grasses
• Grasslands contain about 600 genera and 7,500
species of grasses
• Grasses (Poaceae) occur from the polar regions to
the tropics and comprise about 15% of the
flowering plant species
• Poaceae is third in number of genera behind
Asteraceae and Orchidaceae and fifth in number
of species behind Asteraceae, Orchidaceae,
Fabaceae, Rubiaceae (madder family - coffee and
gardenias)
• Poaceae far surpass all other groups in terms of
worldwide geographic coverage and percentage of
total world vegetation cover
Grasslands
• Grasslands usually develop in areas with 25 to 100
cm of annual precipitation (10 to 40 inches)
• Grasslands are found primarily in plains in the
interiors of continents and occur from sea level to
4,900 meters in the Andes (over 16,000 feet)
• Grasslands are typically located on deep, rich soils
with simple profiles
• The soils are usually neutral to basic, high in
organic matter, and thus are highly fertile
Grasslands Around the World
Grasslands
• 44% of Europe - mostly in the Ukraine, Hungary,
Transylvania – but also in Spain
• 33% of South America - mostly pampas of Argentina but
tallgrass prairie found in Uruguay and central Brazil,
extensive savanna in Brazil
• 29% of Africa - but most is savanna and only 5% is prairie;
most true prairie is in high veld of South Africa, but some
occurs in east Africa
• 17% of Asia - mostly shortgrass steppes (prairies)
• 15% of North America is prairie - there are also more arid
grasslands in western North America
Grasslands in North America
Prairie Limits
• Eastern margin of these grasslands typically has
annual precipitation of 75 - 100 cm from Texas to
Indiana and 50 - 65 cm farther north; roughly 75%
of the precipitation occurs in the growing season
• As we move west, precipitation declines to about
25 cm near the Rockies and up to half of the
precipitation falls out of the growing season
• All North American grasslands have a wet season
followed by a period of drought or dry conditions
- in Illinois, most precipitation occurs in spring,
summer is somewhat drier
Prairie Types
• Decline in precipitation from east to west across
prairies and Great Plains results in the center of
the country having basically 3 different prairie
types
• tallgrass or true prairie where grasses typically
exceed 120 cm; on eastern end with most
precipitation – 60-100 cm precip
• mixed grass prairie with grasses typically between
60 - 120 cm tall occurs in middle region with
intermediate precipitation – 35-60 cm precip
• shortgrass prairie with grasses less than 60 cm tall
- at western margin with least amount of
precipitation – 25-35 cm precip
Prairie Plants
• Like all grasslands, prairies tend to be poor in
diversity at the level of families - with 27% of the
species being grasses - Poaceae; 19% being asters
- Asteraceae; 10% being peas - Fabaceae
• But tallgrass prairie is very rich in numbers of
species - there are about 265 species of grass and
forb native to Illinois's tallgrass prairies - 72 of
those species are grasses
• 95% of the tallgrass prairie plants are perennial
plants with lifespans of around 20 years being
common and some may live for more than a
hundred years
Tallgrass Prairies
• Tallgrass prairie occurs in areas with a ratio of
about 0.6 to 0.8 of precipitation to evaporation;
peak precipitation in fall and spring, less
precipitation in winter and summer;
• occasional droughts which may last up to 10 years
occurring every 30 years or so;
• these climatic factors probably keep most woody
plants out, while the prairie grasses and forbs are
adapted to these "droughty" conditions
Tallgrass Prairie Grasses
• tallgrasses such as big bluestem Andropogon
gerardi, Indiangrass Sorghastrum nutans, switchgrass Panicum virgatum
• mid-grasses such as little bluestem Schizachyrium
scoparius, sideoats grama Bouteloua curtipendula,
porcupine needlegrass Stipa spartea
• shortgrasses such as blue grama Bouteloua
gracilis and hairy grama B. hirsuta
Tall Grasses
Big Bluestem
Indian grass
Switchgrass
Mid grasses
Little Bluestem
Sideoats grama
Porcupine Needlegrass
Short Grasses
Blue grama
Hairy grama
Grass Adaptations to Semi-Arid
Conditions and Grazing
• Leaf cells (bulliform cells) allowed the leaves to
roll up during drought to avoid desiccation
• basal meristem allowed leaves to recover and
grow back following grazing
• basal meristem and silica content (opal) in plants
probably evolved in response to grazing - silica to
prevent or lessen grazing
• petals became modified into structures called
lodicules which enabled the florets (small flowers)
to open when moisture was favorable and close
during times of excess moisture or drought
Bulliform Cells
Leaves curling due to desiccation
– in corn
Worn high crowned tooth
- from horse
More Grass Adaptations
• wind pollination developed because when living in
areas with frequent drought, insect pollinators
would be scarce - also winds are normally strong
here
• grasses became modified to be efficient at asexual
reproduction - clonal growth via runners and
stolons
• seed dispersal by wind - caryopsis modified to
have bristles which catch the wind - also
modifications of caryopsis to allow dispersal by
animals - rough awns and beards that catch on hair
and feathers or skin
• major species have evolved broad tolerances and
subsequently have wide geographic ranges
Climate of Tallgrass Prairies
• Weather is the sum total of the atmospheric
conditions (temperature, air pressure, wind
speed, moisture, and precipitation) over a
short time period
• Climate is a longer term composite of the
variety of day to day weather conditions
Climate in Illinois
Climate in Illinois region is dominated by 4 major air
masses 1. maritime tropical air - warm, moist, unstable from Gulf of Mexico and Caribbean
2. Continental tropical air - hot, dry, unstable - from
northern Mexico and southwestern U.S.
3. Maritime polar air - cool, moist, unstable in
winter, stable in summer - from northern Pacific
4. Continental polar air - cool, dry, stable - from
northern Canadian tundra
Climate Details
• temperature - monthly maximum and minimum are lowest
in January, max of 5.6 C and min of -4.4 C;
• monthly maximum and minimum are highest in July, max
of 26.1 C and min of 13.3 C
• Illinois has about 180 frost free days in the center of the
state - more in the south, fewer in the north
• Precipitation - minimum in January - 1.93 cm; maximum
in June - 11.66 cm; with secondary maximum in
September 10.92 cm
• This dual peak of rainfall is very typical of areas
dominated by tallgrass prairie
Key Climatic Characteristic
• A key climatic
characteristic is the
ratio of precipitation
to evaporation - this is
usually between 0.6
and 0.8 for tallgrass
prairie regions
Microclimate
Soil Conditions
• Maximum soil surface temperatures occur in June at time
of maximum of solar radiation; but maximum soil
temperature at 200 cm depth doesn't occur until
September
• Similarly minimum soil surface temperature occurs in
January, but minimum soil temperature at 200 cm depth
occurs in March - plant roots buffered from rapid and
extreme changes in temperature
• Soil water content is maximum in spring - following rain
and melt; soil water content is minimum in August following period of active growth through somewhat dry
summer