Prairies

Topic: World Physical Features and Natural Regions · NCERT: Class 12, Ch 4 "Primary Activities"

Meaning

The Prairies are the temperate grasslands of North America: wide, nearly treeless plains covered with grass, deep inside the continent in the USA and Canada, east of the Rocky Mountains. They matter because they are the "wheat basket" of the world. Huge machine-run farms there grow wheat and maize for sale, and much of it goes to world markets. That makes the Prairies important for global food supply.

Explanation

Why the Prairies are grasslands: location and climate

• Mid-latitude interior: temperate grasslands lie at about 30°–55° latitude, deep inside continents, far from the sea.
• Moist sea winds drop most of their water before they reach the interior.

• The Rockies to the west also block moist winds coming from the Pacific.

• Continental climate (the type of climate found far from the sea):

• Summers are warm to hot, and short.
• Winters are very cold, with snow on the ground and frequent frost.

• The gap between summer and winter temperatures is very wide.

• Rainfall: 25–75 cm a year. Most of it falls in spring and early summer, often as convectional showers (short, heavy showers from warm air rising on hot days).

• Köppen class: the drier western edges fall under BSk, a cold, semi-arid steppe climate. (Köppen is a way of grouping world climates by temperature and rainfall.)

Soil and vegetation

• Chernozem ("black earth" in Russian): a deep soil with a thick black top layer that is rich in humus (rotted plant matter). It is among the most fertile soils in the world [2].
• It forms where 450–600 mm of rain falls a year, mostly in spring or early summer, with cold winters and short, hot summers [2].

• It covers about 230 million hectares worldwide, mainly in the steppes of Eurasia and the plains of North America [2].

• How chernozem forms:

• Grass roots die every year and add a lot of humus.
• Low rain means little leaching (water washing nutrients down and out of the soil).

• Calcium and humus stay in the top layer, so the soil becomes black and crumbly.

• Chestnut soils are found at the drier margins.

• Vegetation: tall grass in the wetter east, short grass in the drier west. Trees grow only along rivers.
• Why there are few trees:
• Low rain: not enough water for deep-rooted trees.
• Frost: hard winters kill young trees.
• Fire: dry grass burns often. Grass grows back from its roots, but tree seedlings die.
• Grazing: wild bison, and later cattle and sheep, eat young shoots.

The Chinook wind

• Chinook: a warm, dry wind that blows down the eastern slopes of the Rockies in winter and spring.
• Moist air rises over the Rockies, cools, and drops its rain or snow on the western side (the windward side, which faces the wind).
• The now-dry air sinks down the eastern side and warms up as it is squeezed.

• The warm wind can melt snow in hours, so it is called the "snow eater".

• Use to farmers: it clears snow from pastures so animals can graze, and it makes early sowing possible.

Economy: extensive grain farming and ranching

• Extensive commercial grain cultivation: farming on very large, machine-run farms to grow grain, mainly wheat, for sale.
• Land is huge and workers are few, so tractors and combine harvesters do the work.
• Low yield per hectare: each hectare gets little fertiliser and labour.
• High yield per worker: one farmer with machines handles hundreds of hectares.

• The main limit is the harvest season.

• Wheat belts:

• Spring wheat (sown in spring) in the colder north: Canada and North Dakota.
• Winter wheat (sown in autumn) in the milder south: Kansas.

• Maize on the wetter eastern side.

• Livestock ranching: large herds of cattle on big fenced farms (ranches) in the drier parts that are not good for ploughing.

• Railways opened the Prairies. Trans-continental railways (lines that cross the whole continent) brought settlers in and carried grain out to ports. Without them, the interior had no route to world markets.

Where it occurs

• USA: the interior plains east of the Rockies, including the Great Plains.
• Kansas: winter wheat belt (south).
• North Dakota: spring wheat belt (north).

• The south-western Great Plains were the centre of the Dust Bowl of the 1930s [3].

• Canada: the Prairie Provinces, which are Alberta, Saskatchewan and Manitoba. They lie in the spring wheat belt.

• Eastern slopes of the Rockies: where the Chinook wind blows.
• Wetter eastern side: maize-growing areas.
• Related lands elsewhere: chernozem also covers the steppes of Eurasia [2]. The other temperate grasslands are the Pampas (Argentina and Uruguay), Steppes (Ukraine to Mongolia), Velds (South Africa), Downs (Australia), Canterbury Plains (New Zealand) and Puszta (Hungary).
• India: India has no prairie grassland. The Prairie lesson applies to India's dry lands in Rajasthan and the Deccan: keep grass cover, plant shelter belts and match farming to rainfall.

Don't confuse with

• Pampas: also temperate grassland, but in Argentina and Uruguay, around the Rio de la Plata. Its winters are mild, and it is known for wheat, alfalfa (a fodder crop for cattle) and beef from estancias (big ranch-farms). The Prairies have very cold, snowy winters.
• Steppes: the Eurasian temperate grassland, from Ukraine to Mongolia. It exports grain through Black Sea ports and is the traditional home of pastoral nomads (herders who move with their animals to find grass). The Prairies are in North America.
• Savanna / Llanos / Campos: these are tropical grasslands. They are hot all year, have a wet and a dry season, and have tall grass with scattered trees. The Prairies are temperate: cold winters, no trees.
• Foehn: a warm, dry wind like the Chinook, but it blows in the Alps (Europe). The Chinook blows on the eastern slopes of the Rockies.

Prelims Hooks

• Prairies → USA and Canada. The Canadian Prairie Provinces are Alberta, Saskatchewan and Manitoba.
• Chinook = the warm, dry "snow eater" wind on the eastern slopes of the Rockies. The Foehn is the Alpine equivalent.
• Spring wheat grows in the colder north (Canada, North Dakota). Winter wheat grows in the milder south (Kansas).
• Chernozem ("black earth") is the soil of the Prairies, Steppes and Pampas. It forms under 450–600 mm of spring and early-summer rain with cold winters [2].
• Extensive grain farming = low yield per hectare, high yield per worker.
• Trap: the Prairies are temperate. The Llanos (Venezuela and Colombia), Campos (Brazil) and Savanna (Africa) are tropical.

Mains Points

• Breadbasket of the world (GS-I/GS-III):
• Flat land, fertile chernozem, mechanised farms and trans-continental railways to ports produce a huge grain surplus for export.

• Much of the world depends on a few such grasslands, so a drought or price shock here raises food prices everywhere.

• Dust Bowl: misuse of semi-arid grassland (GS-III):

• Cause: farmers ploughed up prairie grass for dryland wheat, and millions more acres were ploughed as demand rose [3].
• Trigger: severe drought hit the south-western Great Plains between 1930 and 1940 [3]. NASA research links it to unusual tropical sea-surface temperatures, made worse by land–air feedback [4].

• Result: bare soil blew away in dust storms, some reaching the Atlantic Ocean, and about 400,000 people left the Great Plains [3][5].

• Lessons and responses (GS-III):

• Keep grass cover.
• Plant shelter belts (rows of trees that break the wind).
• Use contour ploughing (ploughing across a slope, not up and down it).
• The same lessons apply to India's dry lands in Rajasthan and the Deccan. Climate change is expected to make drought risks in such grasslands worse.

Related concepts

• Temperate grasslands of the world
• Pampas
• Steppes
• Velds
• Downs
• Canterbury Plains

Read more

• Natural regions II: temperate grasslands and Mediterranean lands