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Illinois Plant Communities – Prairie Ecosystems. Primary Production. Grasses occur in two basic forms - sod (or turf) grasses form a thick mat - bermuda grass, blue grass bunch grasses grow in distinct clumps - little bluestem, prairie dropseed

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Illinois Plant Communities – Prairie Ecosystems

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primary production
Primary Production
  • Grasses occur in two basic forms - sod (or turf) grasses form a thick mat - bermuda grass, blue grass
  • bunch grasses grow in distinct clumps - little bluestem, prairie dropseed
  • 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 production10
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 productivity16
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 productivity cont d
Prairie Productivity cont’d
  • For most praire plants, 80% of the root biomass occurs in the top 25 cm of soil
  • Further complicating the picture is that many grasses reproduce by rhizomes - the rhizomes anchor the plant, take up some water and nutrients, store food, and produce aerial shoots - rhizomes usually occur in the top 10 to 20 cm of the soil
prairie productivity18
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
compensatory growth
Compensatory Growth
  • Grazing seems to stimulate plants to engage in compensatory growth (to replace lost plant material) and to reallocate resources within the plant
  • Compensatory growth may occur due to enhanced photosynthesis; more efficient light use due to reductions in mutual shading; hormonal changes causing an increase in tillering; leaf cell division and leaf cell expansion; reduced rate of leaf senscence; nutrient recycling accompanying herbivory (excretion releases nutrients); some stimulatory effect of herbivore saliva (this idea about cow slobber is very controversial)
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 grazing31
Decline with grazing

Prairie Vole Short-tailed shrew

unaffected by grazing
Unaffected by grazing

Thirteen-lined ground squirrel White-footed deer mouse

native american fires
Native American Fires

Meadows Burning by George Caitlin - 1832

decline with spring fires
Decline with spring fires

Kentucky Bluegrass

Bicknell’s Sedge

increase with spring fires
Increase with spring fires

Canada Wild Rye

Prairie Dropseed

fire effects
Fire Effects
  • If fire is followed by adequate precipitation, biomass production will increase in the next 2 to 3 years following the fire; if precipitation is less than adequate, biomass production will decrease
  • Species richness of plants usually increases in burned compared to unburned areas - species richness also increases when fire is combined with grazing - so fire and grazing both act to limit growth by competitive dominants and allow competitively inferior species to increase
decrease with fire
Decrease with fire