Case Study: Human Impacts on Prairies

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  • North American popn. existed in harmony with their environment before arrival of Europeans
  • They developed a close relationship with the bison and maintained a suitable hunting and farming economy
  • Europeans came in and removed bison and antelope and replaced it with their cattle
  • Set up a monoculture- the practise of growing the same crop year after year in the same area. Crop the Europeans used was cereal
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Monoculture Impacts on Soil

  • Repeated removal of vegetation takes nutrients from ecosystem disrupting the cycle
  • Ploughing of soil breaks up surface mull humus which damages soil structure making it vulnerable to erosion and loss of humus means soil is less able to retain moisture
  • As part of harvesting process, soil is left bare and is exposed to wind and water erosion
  • Burning crop stubble after a harvest means soil is left bare and exposed to wind and rain
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The Dust Bowl

  • Monoculture and burning crop stubble combined with drought led to extensive erosion throughout the 1930s
  • Soils became dried out and were bare as winds removed 75% of topsoils
  • Badlands of Dakota are so bad that farming is still impossible today
  • 9.5 million hectares of land were in fallow 1981
  • Effects worsened by use of tractors which weakened the soil structure leading to a drop in farmer yield as a result
  • Canadian Prairie farmers lost $100 million in 1984 as a result of soil erosion a 10% drop in farm income
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Monoculture Impacts on Vegetation

  • Reduction in biodiversity- less plants, dropseed and dock replaced with cereal crops- 35 animal species and 350 plant species under threat
  • Reduction in stratification- multi-layered plants replaced by those of one height
  • Deep root system is broken- leaves soil prone to erosion deep root plants replaced with deeper roots
  • EPA suggests overgrazing is repsonsible for 28% of soil erosion
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Soil Conservation Methods- Part 1


  • Material left covering soil- usually DOM
  • Protects soil, increases infiltration and reduces soil loss
  • When plant stubble that remains after harvest is left on fallow lands in Prairies soil loss is much less than if left bare

Contour Ploughing

  • Ploughing fields along contour lines, thereby not creating dust gullies
  • Used in 1935 when Soil Erosion Service paid farmers to use it in flat land eg Nebraska

Cover Crops

  • Planted to protect soil when main crops do not cover ground
  • Instead of resting soil, plants return all nutrients back into the soil- legumes eg peas are used as they can fix nitrogen from the air to the soil
  • Helps improve physical condition of the soil as it reduces wind/water erosion so soil not left bare
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Soil Conservation Methods- Part 2

***** Farming

  • Growing crops in strips alternating with strips of fallow
  • Reduces wind speed on soil and distance wind travels across fallow
  • Used in Saskatchewan eg wind direction is NW or W so best direction for strips to reduce erosion N or S

Shelter Belts

  • Line of trees at edges of fields to act as windbreaks and shelter soil from wind erosion
  • Canadian Permanent Cover Programme offers farmers 10 or 21 year contracts
  • In Manitoba $40 per acre for 10 years or $70 for 21 years
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Soil Conservation Methods- Effectiveness

  • Overall have reduced erosion
  • In 2007 National Resources Inventory (NRI) report said that between 1982 and 2007 soil erosion was reduced by 43% through these methods, although declines in soil erosion have moderated slightly and by 1997 the decline was still downwards
  • In Southern Plains erosion was reduced from 12.5 tonnes per acre in 1981 to 8.8 tonnes per acre in 2007
  • In 2007 9.9 million tonnes were eroded above sustainable rates resulting in the loss of 827 million tonnes of soil per year

Buffalo Commons

  • Suggestions to return to an area of 360,000km2 of natural grassland conditions and original species
  • Gaining popularity  in recent years with Kansas City Star reporting in 2009 a 4000km2 Buffalo Commons park was to be established in western Kansas
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