The Prairie Ecosystem - Supplement

What is a Prairie?

• Dominated by grasslands, seasonal flowers and other forbs, and few or no woody plants
• Level ground or gently rolling hills
• Moderate average rainfall (10” – 30”)
• Moderate temperature (40°F – 60°F)
• In North American, significant variation of rainfall and temperature along latitudinal and longitudinal gradients
• Present on all inhabited continents but most prevalent in central North America, southern South America, and northern Asia

The Historic North American Prairie

Grasses of the Prairie

• Tall grass prairies – Big Bluestem, Switchgrass, Indiangrass
• Mixed grass prairies – Little Bluestem, Wheatgrass, Needlegrass, Sideoats Grama
• Short grass prairies – Blue Grama, Buffalograss

Insect Groups of the Prairie

• Dominant primary consumers
• Extremely important link in every food web of prairie

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• Pollinators, turn and aerate soil, defoliate areas to allow new growth and species diversity

Other Herbivores

Carnivores

North American Prairie Food Chain�

Black-tailed Prairie Dog

Big Bluestem

Prairie Rattlesnake

Coyote

Golden Eagle

Primary

producers

Quaternary

consumers

Tertiary

consumers

Secondary

consumers

Primary

consumers

Decomposers/

Detritivores

Solar Energy

Nutrients

Natural Seasonal Cycles

• Most North American prairies have a seasonal wet/dry cycle where rains come in a few weeks in spring or fall but are otherwise dry
• Rainy season – extreme plant growth and insect activity
• Dry season – vegetation browns and dries; animals leave or reduce activity
• During dry season, vegetation becomes fuel for seasonal fires (lightning)

Fire on the Prairie

Fire is a Disturbance

• Disturbance – in ecology, a temporary change in environmental conditions that causes a pronounced change in an ecosystem
• Seems negative but many ecosystems are tolerant of disturbances or require them to maintain the system
• Prairie fires remove old vegetation, allow soil direct sunlight, let smaller plants bloom, return nutrients to the soil, and remove small woody vegetation
• The prairie ecosystem requires fire to “reset” the system and keep it healthy

The Prairie Without Fire

• As fires burn, young woody shrubs and trees are consumed and removed from the community
• Grasses thrive, forbs grow better in absence of trees, and the whole system remains healthy
• When humans began suppressing fire, woody vegetation grew to maturity and encroached on the prairie
• Shaded areas couldn’t support grass
• Trees consumed more water than grasses and forbs
• The community suffered because of lack of fire
• Invasive species are able to establish populations

Loss of Prairie Habitat

• The tallgrass prairie is most imperiled
• Conversion to cropland
• Fertile soils excellent for corn, wheat, and soy bean
• Suppression of fire
• Woody encroachment
• Development for city and infrastructure

• ~1% of tallgrass prairie intact
• ~24% of mixed grass prairie intact
• ~18% of short grass prairie intact

So What?

• Loss of the prairie results in:
• Reduction of native habitat for insects, birds, and mammals
• Destabilization of communities
• Food webs, primary production, invasive species, reduction of diversity
• Soil moisture loss causes loss of topsoil, increase in weather extremes, and increased risk of flooding
• Dust bowl of 1930s