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  • In climates that have less rainfall, forest biomes are replaced bysavanna, grassland, and chaparral biomes. As less rain falls inthese biomes, they change into desert and tundra biomes. As pre-cipitation decreases in an area, the diversity of the species in thearea also decreases. But while the number of different species isoften smaller in areas that have less precipitation, the number ofindividuals of each species present may be very large.

    SavannasParts of Africa, western India, northern Australia, and some partsof South America are covered by grassland called savanna.

    are located in tropical and subtropical areas near theequator and between tropical rain forest and desert biomes.Because savannas are full of grasses, scattered trees, and shrubs,savannas contain a large variety of grazing animals and the preda-tors that hunt them. As shown in Figure 16, savannas receive lit-tle precipitation throughout the year. Savannas have a wet seasonand a dry season. Many animals of the savanna are active onlyduring the wet season. Grass fires sweep across the savanna dur-ing the dry season and help restore nutrients to the soil.

    Plants of the Savanna Because most of the rain falls duringthe wet season, plants must be able to survive prolonged pe-riods without water. Therefore, some trees and grasses havelarge horizontal root systems by which they obtain water dur-ing the dry season. These root systems also enable plants toquickly grow again after a fire. The coarse savanna grasseshave vertical leaves that expose less of their surface area to thehot sun to further help the grasses conserve water. Some treesof the savanna also lose their leaves during the dry season toconserve water. Trees and shrubs often have thorns or sharpleaves that keep hungry herbivores away.

    Savannas

    Objectives Describe the difference between

    tropical and temperate grasslands. Describe the climate in a chaparral

    biome. Describe two desert animals and

    the adaptations that help themsurvive.

    Describe one threat to the tundrabiome.

    Key Termssavannatemperate grasslandchaparraldeserttundrapermafrost

    S E C T I O N 3

    Grassland, Desert, and Tundra Biomes

    Tropical Savanna(Nairobi, Kenya)

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    Figure 16 Savannas have periodsof heavy rainfall followed by periodsof drought.

    Section 3 Grassland, Desert, and Tundra Biomes 155Copyright by Holt, Rinehart and Winston. All rights reserved.

  • Animals of the Savanna Grazing herbivores such as the elephantsshown in Figure 17, have adopted a migratory way of life. Theyfollow the rains to areas of newly sprouted grass and wateringholes. Some predators follow and stalk the migratory animals forfood. Many savanna animals give birth only during the rainy sea-son, when food is most abundant and the young are more likely tosurvive. Also, some species of herbivores reduce competition forfood by eating vegetation at different heights than other species do.For example, small gazelles graze on grasses, black rhinos browseon shrubs, and giraffes feed on tree leaves.

    Temperate GrasslandsA is a biome that is dominated by grassesand that has very few trees. Most temperate grasslands have hotsummers and cold winters. The amount of rainfall that a temper-ate grassland receives is moderate compared to the amount a for-est receives. On average, a temperate grassland can receive 50 to88 cm of precipitation per year, as shown in Figure 18. Althoughtemperate grasslands may seem harsh and dry, they have the mostfertile soil of any biome. So, many grassland biomes have beenreplaced with crops such as corn, soybeans, and wheat. Few natu-ral temperate grasslands remain because many have been replacedby farms and grazing areas.

    temperate grassland

    156 Chapter 6 Biomes

    Figure 17 Herbivores of thesavanna reduce their competition forfood by feeding on vegetation locatedat different heights. Elephants feed ontree leaves, while impala graze ongrasses.

    Temperate Grassland(Wichita, Kansas)

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    Figure 18 Temperate grasslandsare characterized by small amountsof rainfall, periodic droughts, andhigh temperatures in the summer.

    GeofactDeep Soil Gravel or sand becomesfertile soil when decomposersslowly break down organic mattersuch as dead leaves. Decomposerswork most effectively in hot, wetweather. As a result, the worldsdeepest soil is in grasslands. Ingrassland biomes, winters are coldand summers are dry, which causesleaves to break down slowly. So,organic matter builds up over time.Some North American prairies hadmore than 2 m of topsoil when thefirst farmers arrived.

    Copyright by Holt, Rinehart and Winston. All rights reserved.

  • Temperate grasslands are located on the interiors of continentswhere too little rain falls for trees to grow. Grassland biomesinclude the prairies of North America, the steppes of Russia andUkraine, and the pampas of South America, as shown in Figure 19.Mountains often play a crucial role in maintaining grasslands. Forexample, in North America, rain clouds from the west are blockedby the Rocky Mountains, so the shortgrass prairie east of the moun-tains receives only about 25 cm of rain a year. Rainfall increases asyou move eastward, so taller grasses and some shrubs can grow inareas where more rain falls. Heavy precipitation is rare in the grass-lands, so sizzling temperatures in the summer make the grasslandssusceptible to fires, which are common in grassland biomes.

    Plants of Temperate Grasslands Prairie grasses and wildflowersare perennials, plants that survive from year to year. The root sys-tems of prairie grasses form dense layers that survive drought andfire as well as hold the soil in place. The amount of rainfall in anarea determines the types of plants that will grow in that area.Figure 20 shows how root depth and grass height vary dependingon the amount of rainfall. Few trees survive on the grasslandsbecause of the lack of rainfall, fire, and the constant winds.

    Section 3 Grassland, Desert, and Tundra Biomes 157

    Figure 19 Temperate grasslandscan be named according to the vege-tation that grows there. Steppes (left),have shorter grasses and are located inEurope and Asia. Pampas (right), aremade up of clusters of feathery grassesand are located in South America.

    HistoryConnection to

    The State of Bison More than60 million bison once roamed thetemperate grasslands of NorthAmerica. But these large grass-eating mammals were almostbrought to extinction by the late1800s because of hunting bywestern settlers. By 1889, fewerthan 1,100 bison remained inNorth America! The first bill tosave the bison was introduced byCongress in 1874. In 1903,President Theodore Rooseveltstarted the National WildlifeRefuge System to provide pro-tected areas for bison and otheranimals. Today, North Americahas more than 200,000 bison.

    Shortgrass prairie(about 25 cm rain per year)

    Mixed or middlegrass prairie

    (about 50 cm rain per year)

    Tallgrass prairie(up to 88 cm rain per year)

    Figure 20 The height of grasslandplants and the depth of their rootsdepend on the amount of rainfallthat the grasslands receive.

    Copyright by Holt, Rinehart and Winston. All rights reserved.

  • Animals of Temperate Grasslands Grazing animals, such aspronghorn antelope and bison, have large, flat back teeth forchewing the coarse prairie grasses. Other grassland animals, suchas badgers, prairie dogs, and owls, live protected in undergroundburrows as shown in Figure 21. The burrows shield the animalsfrom fire and weather and protect them from predators on theopen grasslands.

    Threats to Temperate Grasslands Farming and overgrazing havechanged the grasslands. Grain crops cannot hold the soil in placeas well as native grasses can because the roots of crops are shal-low, so soil erosion eventually occurs. Erosion is also caused byovergrazing. When grasses are constantly eaten and trampled, thegrasses cannot regenerate or hold the soil. This constant use canchange fruitful grasslands into less productive, desertlike biomes.

    ChaparralPlants that have leathery leaves are commonly found in temperatewoodland biomes. Temperate woodland biomes have fairly dryclimates but receive enough rainfall to support more plants thana desert does. Temperate woodlands consist of scattered treecommunities made up of coniferous trees such as pion pines andjunipers, as shown in Figure 22.

    is a type of temperate woodland biome that is dominated by more broad-leafed evergreen shrubs than by ever-green trees. Look at the famous white letters that spell Hollywood

    Chaparral

    158 Chapter 6 Biomes

    Figure 21 Prairie dogs, such asthose shown here, live in temperategrasslands. Prairie dogs live incolonies and burrow in the groundto build mounds, holes, and tunnels.

    Figure 22 Temperate woodlandsare usually too dry to support a for-est, but they receive sufficient pre-cipitation to support vegetation thatgrows in bunches, such as the pionand juniper trees shown here.

    QuickLABSponging It UpProcedure1. Completely saturate two small

    sponges with water and allowthe excess water to drain off.

    2. Measure each sponges mass byusing an electr