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Illinois Plant Communities – Prairie Ecosystems. 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

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prairie limits
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
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
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 prairie grasses
Tallgrass Prairie Grasses
  • tallgrasses such as big bluestem Andropogon gerardi, Indiangrass Sorghastrum nutans, switch-grass 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
Tall Grasses

Big Bluestem Indian grass Switchgrass

mid grasses
Mid grasses

Little Bluestem Sideoats grama Porcupine Needlegrass

short grasses
Short Grasses

Blue grama Hairy grama

grass adaptations to semi arid conditions and grazing
Grass Adaptations to Semi-Arid Conditions and Grazing
  • Leaf 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
more grass adaptations
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
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

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
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
Key Climatic Characteristic
  • A key climatic characteristic is the ratio of precipitation to evaporation - this is usually between .6 and .8 for tallgrass prairie regions
primary production
Primary Production
  • Grasses occur in two basic forms - sod (or turf) grasses form a thick mat - bermuda grass
  • bunch grasses grow in distinct clumps - little bluestem
  • sod grasses usually grow vegetatively with short rhizomes, stolons or runners and are very effective in resisting water or wind erosion
  • bunch grasses reproduce vegetatively by tillers - shoots which arise from the crown - basal portion of plant, atop the roots - may have up to 100 or more tillers in a single clump of grasses like little bluestem
primary production1
Primary Production
  • Gross primary production (GPP) is the total amount of energy fixed by a plant or plant community
  • Net primary production - is the amount of energy stored or biomass produced - it is GPP minus energy burned in respiration
  • NPP = GPP - R
ecosystem production
Ecosystem Production
  • Gross Ecosystem Production (GEP) - is total energy fixed in ecosystem
  • Net ecosystem production (NEP) is total amount of energy stored or biomass produced by all organisms in ecosystem - producers, consumers, decomposers - or GEP - ecosystem respiration (ER) the respiration of all plants, consumers and decomposers
  • NEP = GEP - ER
prairie productivity
Prairie Productivity
  • Estimates of production of aboveground biomass range from 200 to 570 grams of carbon per square meter per year for a tallgrass prairie
prairie productivity1
Prairie Productivity
  • In prairies 2 to 4 times the amount of aboveground biomass occurs as biomass below ground
  • Prairie plants produce extensive root systems - big bluestem roots reach down 2 m; switchgrass roots reach down 3.7 m; forbs such as leadplant and dotted gayfeather have much deeper roots - reaching down 5 m
  • A student of Weaver's measured the length of root material in the top 10 cm of a 0.5 square meter plot and found 21.5 km of big bluestem root; 38.7 km of little bluestem; 18.3 km of needlegrass; 176.7 km of Kentucky bluegrass
prairie productivity2
Prairie Productivity
  • In prairies belowground biomass of 685 to 1900 g C per square meter per year
  • Thus total yearly production in tallgrass prairies combining aboveground and belowground biomass appears in the 800 to 2400 g C per square meter per year range
  • This is in comparison to 3500 g C per square meter for an Iowa cornfield
grazing in illinois prairies
Grazing in Illinois Prairies

Illinois tallgrass prairie plants vary in response to grazing - ability to withstand grazing depends upon several factors:

1. possession of rhizomes

2. capacity for production of lateral shoots

3. small height and erectness of growth habit

4. lateness of seed germination and spring growth

5. slow growth rate

6. lateness of elevation of stem apex above minimum point of grazing

decline with grazing
Decline with Grazing

Indian grass Willow aster

increase with grazing
Increase with Grazing

Sideoats grama Common Yarrow

highly invasive after grazing
Highly invasive after grazing

Downy Brome (cheatgrass) Canada Thistle


Eastern Meadowlark Dickcissel

Increase with moderate grazing


Grasshopper sparrow –

Only found in grazed areas


Savannah sparrow

Declines with grazing


LeConte’s Sparrow Bobolink

Unaffected by grazing

decline with grazing1
Decline with grazing

Prairie Vole Short-tailed shrew

unaffected by grazing
Unaffected by grazing

Thirteen-lined ground squirrel White-footed deer mouse