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