Grasslands

Grassland-an ecosystem in which there is more water than in a desert, but not enough water to support a forest

• Grasslands start at the edge of desert biome and stretch across the land to the forest biome

• Found in Africa, central Asia, North America, South America, and Australia

• In US, they stretch from Rocky Mountains in west to forests of the East

• Stretch from Canada down to Mexico• CLIMATE• Wetter than deserts• The dry air that blows over the east of the mountain to form

deserts, eventually gains enough moisture for rain to fall • Desert-grassland boundary-the area b/n deserts and

grasslands where increased rainfall enables some grasses to grow

• Long-term climate changes can cause biome changes• If enough rain falls, a desert can become a grassland• If rainfall decreases enough, a grassland can become a desert

• ORGANISMS• Both abiotic and biotic factors determine what organisms live in

grasslands• Grasses are the most common• ABIOTIC FACTORS• Hot, dry summers• Rainfall is the limiting factor• w/out rain, grass won’t develop• Also, natural fires caused by lightning limit grassland

development• Fires are common and keep # of trees and shrubs low• Most mass of trees and shrubs are aboveground, so they are

vulnerable to fire• Grasses have most mass below ground, so they survive better• Rye plant is 2 meters high, but has 600 km of roots below

• Fires also benefit grasslands by burning dead grass layer, making it into valuable nutrients

• Nutrients create a fertilizer• Grasslands have a deep, fertile soil• Heat from fire helps germinate grass seeds• BIOTIC FACTORS• Grazing animals, ex: bison, are lawn mowers keeping

vegetation low to ground• This keeps trees and shrubs too damaged to grow well• Burrowing animal, ex: earthworms, prairie dogs, and insects,

make tunnels and dig.• This aerates the soil, giving more oxygen and nutrients to the

grasses growing roots• Rain amounts affect size and texture of grasses• Short-grass prairies receive less rain• Used for cattle grazing and irrigated crops• Tall-grass prairies receive more rain• Used for tall crops like corn and wheat

• When it rains is also important• Grasslands have rainy seasons and drought seasons• Experience cycles of heavy rain followed by long periods of little

or no rain• Many plants adapted by becoming drought-resistant-trees

and shrubs that survive in dry grasslands despite small amounts of rain

• ANIMALS• All grasslands have large grazing animals: antelope and bison• They can run quickly from predators• Many animals feed on seeds and leaves of grass:

grasshoppers, mice, gophers, prairie dogs, birds

• Some animals are nocturnal to avoid predators and daytime heat,

• They burrow underground• North American predators: coyotes, foxes, snakes, and birds• Grasslands can be three types of biomes: steppe, prairie,

savanna

Types of Grasslands• Steppes• Grasslands of short bunchgrasses that

gets less than 50cm of rain/year• Must get more than 25cm rain/year or

else it’s a desert• Temperatures range b/n -5 degrees and

30 degrees Celcius• Bunchgrasses-short, fine-bladed grasses

that grow in a clump

• Prairies• Grasslands characterized by rolling hills,

plains, and sod-forming grasses• Most grains grow here to make breads and

cereals• 50-75 cm of rain/yr• Have sod-forming grasses- grasses that

form a mat of soil and roots• This keeps soil close together and less

moisture will evaporate• Also has a humus layer-layer of organic

matter made from dead roots of the grasses

• Humus provides fertile and moist layer

• Savannas• Tropical or subtropical grasslands ranging from

dry scrubland to wet, open woodland• Have rainy seasons and long droughts• Up to 150 cm rain/yr during short rainy season• Plants must be resistant to drought, fires, and

grazing animals• Plants have runners-long, horizontal stems

above and below ground• Grasses grow in tufts-large clumps of tall,

coarse grasses• Tufts help protect them from grazing animals• Animals often eat in vertical feeding pattern-

animals eat at different heights• this allows many animals to feed in the same

area