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Illinois Plant Communities – Prairie Ecosystems.

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Presentation on theme: "Illinois Plant Communities – Prairie Ecosystems."— Presentation transcript:

1 Illinois Plant Communities – Prairie Ecosystems


3 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

4 Sod grass vs. bunch grass


6 Grass Tillers

7 Grass Tillers in a Sod Grass

8 Grass Rhizomes

9 Rhizomes and Tillers Stabilizing Soil

10 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

11 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

12 Photosynthesis

13 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



16 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

17 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

18 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

19 Influence of grazing

20 East African Grasslands

21 Grazing in East Africa

22 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)

23 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

24 Decline with Grazing Indian grass Willow aster

25 Increase with Grazing Sideoats gramaCommon Yarrow

26 Highly invasive after grazing Downy Brome (cheatgrass) Canada Thistle

27 Eastern Meadowlark Dickcissel Increase with moderate grazing

28 Grasshopper sparrow – Only found in grazed areas

29 Savannah sparrow Declines with grazing

30 LeConte’s SparrowBobolink Unaffected by grazing

31 Decline with grazing Prairie Vole Short-tailed shrew

32 Unaffected by grazing Thirteen-lined ground squirrelWhite-footed deer mouse

33 Influence of Fire


35 Native American Fires Meadows Burning by George Caitlin - 1832



38 Decline with spring fires Kentucky BluegrassBicknell’s Sedge

39 Increase with spring fires Canada Wild RyePrairie Dropseed

40 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

41 Increase with fire - Prairie Grasshoppers

42 Decrease with fire BeetlesLeafhoppers

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