Desertification in North America The Great Plains (The Dustbowl)

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Desertificati Desertificati on in North on in North America America The Great Plains The Great Plains (The Dustbowl) (The Dustbowl)

Transcript of Desertification in North America The Great Plains (The Dustbowl)

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DesertificatioDesertification in North n in North AmericaAmericaThe Great PlainsThe Great Plains

(The Dustbowl)(The Dustbowl)

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Background to the Dust Background to the Dust Bowl 1Bowl 1

Despite more than 50 years of soil conservation Despite more than 50 years of soil conservation practice, soil erosion remains one of the USA’s practice, soil erosion remains one of the USA’s

most severe environmental problems.most severe environmental problems.

Moderate25 - 75% of topsoil lost

Severemore than 75% of topsoil lost

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Background to the Dust Background to the Dust Bowl 2Bowl 2

About one-third of the cropland in the USA About one-third of the cropland in the USA is now suffering a decline in long term is now suffering a decline in long term productivity which will eventually reduce productivity which will eventually reduce US exports on food.US exports on food.

The Great Plains (also know as The The Great Plains (also know as The Dustbowl) is a case study dealing with a Dustbowl) is a case study dealing with a major incidence of soil erosion.major incidence of soil erosion.

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Location (p.90)Location (p.90)

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The Grasslands The Grasslands EnvironmentEnvironment

Like the African Sahel, the interior Like the African Sahel, the interior grasslands of North America grasslands of North America

cover an immense area. They cover an immense area. They extend nearly 4000km from extend nearly 4000km from

Texas in the south to Alberta in Texas in the south to Alberta in the north at least 800km from the north at least 800km from

east to west.east to west.

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VegetationVegetation

The grasslands are limited by deserts in the The grasslands are limited by deserts in the south and coniferous forests in the north.south and coniferous forests in the north.

The area is covered by various species of The area is covered by various species of grass e.g. buffalo grass and needle grass.grass e.g. buffalo grass and needle grass.

Along rivers, trees such as willow and Along rivers, trees such as willow and cottonwood can grow in the wetter soilscottonwood can grow in the wetter soils..

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Climate 1Climate 1

This ranges from sub-humid in the This ranges from sub-humid in the east to semi-arid in the west.east to semi-arid in the west.

Annual rainfall varies between 350-Annual rainfall varies between 350-750mm over the whole area, but 750mm over the whole area, but occurs mostly during the summer.occurs mostly during the summer.

Summer temperatures over 30ºC are Summer temperatures over 30ºC are common often resulting in a moisture common often resulting in a moisture deficit between June and September.deficit between June and September.

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Climate 2Climate 2

Winter temps range from 10ºC in the Winter temps range from 10ºC in the south to -10ºC in the north.south to -10ºC in the north.

Late winter and early spring is when Late winter and early spring is when soil moisture has a chance to soil moisture has a chance to recharge from the soil melt.recharge from the soil melt.

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Soil 1 - EastSoil 1 - East

Vegetation and soil are strongly influenced Vegetation and soil are strongly influenced by by moisture availabilitymoisture availability..

Higher moisture availability allows Higher moisture availability allows taller taller grassesgrasses to grow (up to 2m). Being short- to grow (up to 2m). Being short-lived this allows large amounts of organic lived this allows large amounts of organic debris to accumulate.debris to accumulate.

This material quickly turns into This material quickly turns into humushumus and and provides both provides both nutritionnutrition for the plants and for the plants and cohesioncohesion for the soil. for the soil.

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Soil 2 - WestSoil 2 - West

By contrast, the west is By contrast, the west is characterised by characterised by shorter grass shorter grass species therefore species therefore less organic less organic materialmaterial is produced making the is produced making the humus layer shallow humus layer shallow and more and more suitable for ranching.suitable for ranching.

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Physical Causes of Physical Causes of Soil ErosionSoil Erosion

Relief

Climate

Vegetation

Sandy Soils

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Human Causes of Human Causes of Soil ErosionSoil Erosion

Overcultivation

Monoculture

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The Dust Storm’s of the 1930’sThe Dust Storm’s of the 1930’s

http://www.youtube.com/watch?v=csnY0Tnvdj8

NOTE DOWN ANYTHING THAT YOU NOTICE FROM THE VIDEO

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What did you spot in the What did you spot in the video?video?

Poor visibilityPoor visibility

People struggling to People struggling to stand up (using the stand up (using the fence to get along)fence to get along)

Things blowing Things blowing everywhereeverywhere

Massive clouds of Massive clouds of dustdust

Dangerous driving Dangerous driving conditionsconditions

Large build up Large build up (dunes) of soil & (dunes) of soil & dustdust

Houses covered in Houses covered in soil & dustsoil & dust

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How did the Dust Bowl How did the Dust Bowl Occur?Occur?

Events took a serious turn for the worse in 1915.Events took a serious turn for the worse in 1915.

Until then Russia was America’s major rival as a Until then Russia was America’s major rival as a wheat exporter.wheat exporter.

BUT Russia’s output was interrupted by World War I.BUT Russia’s output was interrupted by World War I.

The world price for wheat went up by 210% The world price for wheat went up by 210% between 1914 and 1917.between 1914 and 1917.

Many American farmers made large profits from Many American farmers made large profits from producing the hard wheat which the world needed producing the hard wheat which the world needed for bread making.for bread making.

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How did the Dust Bowl How did the Dust Bowl Occur? Occur?

In 1931 another cycle of drought occurred.In 1931 another cycle of drought occurred.

By the spring of 1934, the plains surface had By the spring of 1934, the plains surface had become so dry that wind storms were able to become so dry that wind storms were able to carry gigantic clouds of soil particles right across carry gigantic clouds of soil particles right across the eastern half of the United States.the eastern half of the United States.

Large areas of Kansas, Oklahoma, Texas, Large areas of Kansas, Oklahoma, Texas, Colorado and New Mexico were devastated by Colorado and New Mexico were devastated by topsoil loss during the years 1932-36.topsoil loss during the years 1932-36.

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Days with dust storms during March Days with dust storms during March 19361936

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What Happened Next?What Happened Next?

Hundreds and thousands of rural dwellers abandoned Hundreds and thousands of rural dwellers abandoned the grasslands.the grasslands.

A large proportion of these came from western A large proportion of these came from western Oklahoma, but migrants left every state on the plains.Oklahoma, but migrants left every state on the plains.

They moved to the Pacific coast and to the industrial They moved to the Pacific coast and to the industrial cities of the north-east.cities of the north-east.

While most managed to sell there farms, a large While most managed to sell there farms, a large minority simply gave up there family land.minority simply gave up there family land.

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Dust Storm ManagementDust Storm Management

The Dust bowl catastrophe of the 1930s The Dust bowl catastrophe of the 1930s led the USA Government to establish the led the USA Government to establish the Soil Conservation Service (SCS).Soil Conservation Service (SCS).

The main aim of the SCS is to ensure that, The main aim of the SCS is to ensure that, as far as possible, soil is not lost.as far as possible, soil is not lost.

Over the years it has adopted a number of Over the years it has adopted a number of strategies to help achieve this.strategies to help achieve this.

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Shelter BeltsShelter Belts

Trees planted to act as Trees planted to act as windbreaks to protect windbreaks to protect crops.crops.

As well as trees long As well as trees long rooted, drought rooted, drought resistant grasses were resistant grasses were also planted.also planted.

Protected cropsProtected crops Anchored the soilAnchored the soil Increase humus contentIncrease humus content

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How do sunflowers help?How do sunflowers help?

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IrrigationIrrigation

Drip irrigation is Drip irrigation is used extensively used extensively in dryer areas to in dryer areas to help keep soil help keep soil moist.moist.

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Encouraged Snow?Encouraged Snow?

Snow helps insulate Snow helps insulate soil.soil.

Provides soils with Provides soils with moisturemoisture

Stops soil blowing Stops soil blowing awayaway

Natural snow fencesNatural snow fences

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Changes in agricultural Changes in agricultural practicepractice

FallowingFallowing - to help retain moisture - to help retain moisture and restore soil fertility.and restore soil fertility.

DiversificationDiversification of agriculture - crop of agriculture - crop rotation instead of monoculture to rotation instead of monoculture to maintain soil fertility.maintain soil fertility.

Return marginal areasReturn marginal areas to grass to grass (roots anchor soil).(roots anchor soil).

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Contour Strip CroppingContour Strip Cropping

Prevent formation of Prevent formation of rills and gullies by rills and gullies by rainwater.rainwater.

Different crops often Different crops often planted in strips - planted in strips - harvested at different harvested at different times - helps protect times - helps protect the soil.the soil.

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Task Task

Read p.93-96Read p.93-96

Add summary notes on Laser levelling, Add summary notes on Laser levelling, Minimum Tillage, cell grazing, bison Minimum Tillage, cell grazing, bison ranching.ranching.

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Groundwater Mining 1Groundwater Mining 1

Under the great plains is a vast geological Under the great plains is a vast geological formation called the Ogallala aquifer, formation called the Ogallala aquifer, where valuable water is stored naturally. where valuable water is stored naturally.

During the Dust bowl disaster pumping During the Dust bowl disaster pumping equipment was not widely available to equipment was not widely available to allow farmers to exploit sources of deep, allow farmers to exploit sources of deep, underground water.underground water.

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Groundwater Mining 2Groundwater Mining 2

By the late 1940s technological advances By the late 1940s technological advances gave thousands of farmers access to water gave thousands of farmers access to water supplied through centre pivot sprinklers.supplied through centre pivot sprinklers.

This enabled farmers to grow irrigated This enabled farmers to grow irrigated corn and wheat in the semi-arid western corn and wheat in the semi-arid western plains.plains.

http://www.youtube.com/watch?v=o7Uwg8BT6qQ

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BUT there was a price to BUT there was a price to paypay

To install centre pivot systems many To install centre pivot systems many shelter belts had to be destroyed.shelter belts had to be destroyed.

Overall withdrawal from the aquifer is about Overall withdrawal from the aquifer is about 8 times faster than the rate of recharge.8 times faster than the rate of recharge.

Estimates suggest the aquifer will be Estimates suggest the aquifer will be pumped dry by 2020.pumped dry by 2020.

THE DUST CLOUDS WILL RETURNTHE DUST CLOUDS WILL RETURN

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Failure of the Soil Failure of the Soil Conservation Service Conservation Service

(SCS)(SCS)By 1960 it had become a bureaucratic By 1960 it had become a bureaucratic organisation with soil conservation organisation with soil conservation becoming less of a national priority.becoming less of a national priority.

But in 1970 soil losses once more became But in 1970 soil losses once more became a key issue due to 3 major trends;a key issue due to 3 major trends;

1. Great Plains farming had become 1. Great Plains farming had become fully fully industrialisedindustrialised with with short-term profitshort-term profit being being seen as more important than maintenance seen as more important than maintenance of soil quality.of soil quality.

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Failure of the Soil Failure of the Soil Conservation Service Conservation Service

(SCS)(SCS)

2.2. Good quality farmland was being Good quality farmland was being lost lost to other usesto other uses e.g. suburban sprawl, new e.g. suburban sprawl, new roads, refuse dumps and open-cast roads, refuse dumps and open-cast mining. Equivalent to 2000ha per day.mining. Equivalent to 2000ha per day.

3.3. Due to the Due to the vast surplusesvast surpluses of grain of grain being accumulated the USA being accumulated the USA Government paid farmers to keep their Government paid farmers to keep their land out of production.land out of production.

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Any Any Questions?Questions?

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http://www.youtube.com/watch?v=1UkObwoheS0‘surviving the dustbowl’ documentary. (transcript is in the rural land degradation folder)