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

• 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

Sod grass vs. bunch grass

Grass Tillers

Grass Tillers in a Sod Grass

Grass Rhizomes

Rhizomes and Tillers Stabilizing Soil

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

• 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

Photosynthesis

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 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

• 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 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

Influence of grazing

East African Grasslands

Grazing in East Africa

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

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

1. possession of rhizomes2. capacity for production of lateral shoots3. small height and erectness of growth habit4. lateness of seed germination and spring growth5. slow growth rate6. lateness of elevation of stem apex above

minimum point of grazing

Decline with Grazing

Indian grass Willow aster

Increase with Grazing

Sideoats grama Common Yarrow

Highly invasive after grazing

Downy Brome (cheatgrass) Canada Thistle

Eastern Meadowlark DickcisselIncrease with moderate grazing

Grasshopper sparrow –Only found in grazed areas

Savannah sparrow Declines with grazing

LeConte’s Sparrow BobolinkUnaffected by grazing

Decline with grazing

Prairie Vole Short-tailed shrew

Unaffected by grazing

Thirteen-lined ground squirrel White-footed deer mouse

Influence of Fire

Native American Fires

Meadows Burning by George Caitlin - 1832

Decline with spring fires

Kentucky Bluegrass Bicknell’s Sedge

Increase with spring fires

Canada Wild Rye Prairie Dropseed

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

Increase with fire -Prairie Grasshoppers

Decrease with fire

Beetles Leafhoppers