Figure 17 Desert organisms haveadaptations that enable them to livein the harsh conditions of theirbiome. For example, this shovel-snouted lizard "dances" to avoidburning its feet on the hot sanddunes of the Namib Desert in Africa.Making Generalizations Describe theclimate conditions of a typical desert.

The number of insect species in tropical rain forests is not known,but has been estimated to be in the millions. These in turn feedmany bird species, which feed other animals. Although tropicalrain forests cover only a small part of the planet, they probablycontain more species of plants and animals than all the other landbiomes combined.

Temperate Rain Forests The land along the northwesterncoast of the United States resembles a tropical rain forest in someways. This region receives more than 300 centimeters of rain ayear. Huge trees grow there, including cedars, redwoods, andDouglas firs. However, it is difficult to classify this region. It is toofar north and too cool to be a tropical rain forest. Instead manyecologists refer to this ecosystem as a temperate rain forest. Theterm temperate means having moderate temperatures.

Desert BiomesThe next stop on your expedition is a desert. It couldn't be moredifferent from the tropical rain forest you just left.You step off thebus into the searing summer heat. At midday, you cannot evenwalk into the desert-the sand feels as hot as the hot water thatcomes from your bathroom faucet at home.

A desert is an area that receives less than 25 centimeters ofrain per year. The amount of evaporation in a desert is greaterthan the amount of precipitation. Some of the driest deserts

may not receive any rain at all in a year! Deserts oftenalso undergo large shifts in temperature during the

course of a day. A scorching hot desert like the

Namib Desert cools rapidly each night when the sun goes down.Other deserts, such as the Gobi in central Asia, are cooler, evenexperiencing freezing temperatures in the winter.

The organisms that live in the desert are adapted to the lackof rain and to the extreme temperatures. For example, thetrunk of a saguaro cactus has folds that work like the pleats inan accordion. The trunk of the cactus expands to hold morewater when it is raining. Many desert animals are most activeat night when the temperatures are cooler. A gila monster, forinstance, spends much of its time in a cool undergroundburrow. It may go for weeks without coming up to the surfaceof the desert.

wfe~ What are some adaptations that help an organismto live in the desert?

Grassland BiomesThe next stop on the expedition is a grassland called a prairie. Thetemperature here is much more comfortable than that in thedesert. The breeze carries the scent of soil warmed by the sun. Thisrich soil supports grass as tall as you and your classmates. Sparrowsflit among the grass stems, looking for their next meal. Startled byyour approach, a rabbit quickly bounds away.

Like other grasslands located in the middle latitudes, this prairiereceives more rain than deserts, but not enough for many trees togrow. A grassland receives between 25 and 75 centimeters of raineach year, and is typically populated by grasses and other non-woody plants. Grasslands that are located closer to the equator thanprairies, called savannas, receive as much as 120 centimeteFS of

-Til • .sDesert SurvivalgUseaUhand lensto carefully observe a smallpotted cactus. Be careful of thespines! With a pair of scissors,carefully snip a small piecefrom the tip of the cactus.Observe the inside of theplant. Note any characteristicsthat seem different from thoseof other plants.Observing How is the insideof the cactus different fromthe outside? Suggest how thefeatures you observe might berelated to its desert habitat.

Figure 18 Migratingwildebeest make theirway across a vastKenyan savanna.

Chapter 2 E. 65

Forest Biomes

• Deciduous forest • Boreal forest

Figure 19 This Michigan forestin autumn is a beautiful exampleof a deciduous forest. Thecloseup shows a red fox, acommon resident of NorthAmerican deciduous forests.Comparing and Contrasting Howdo deciduous forests differ from rainforests?

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rain each year. Scattered shrubs and small trees grow on savannasalong with the grass.

Grasslands are home to many of the largest animals onEarth-herbivores such as bison, antelopes, zebras, rhinoceros,giraffes, and kangaroos. Grazing by these large herbivores helps tomaintain the grasslands. They keep young trees and bushes fromsprouting and competing with the grass for water and sunlight.

Deciduous Forest BiomesYour trip to the next biome takes you to another forest. It is nowlate summer. Cool mornings here giveway to warm days. Severalmembers of the expedition are busy recording the numerous plantspecies. Others are looking through their binoculars, trying toidentify the songbirds in the trees. You step carefully to avoid asmall salamander on the forest floor. Chipmunks chatter at allthe disturbance.

You are now visiting the deciduous forest biome. The treesfound in this forest, called deciduous trees (dee SIJ 00 us), shedtheir leaves and grow new ones each year. Oaks and maples areexamples of d~iduous trees. Deciduous forests receive enoughrain to support the growth of trees and other plants, at least 50centimeters per year. Temperatures vary during the year. Thegrowing season usually lasts five to six months. As in the rainforest, different plants grow to different heights, ranging from acanopy of tall trees to small ferns and mosses on the forest floor.

The variety of plants in the forest creates many different habi-tats. You and your classmates note that different species of birdslive at each level, eating the insects and fruits that live and growthere. You observe opossums, mice, and a skunk looking for foodin the thick layer of damp leaves on the ground. Other commonNorth American deciduous forest species include wood thrushes,white-tailed deer, and black bears.

If you were to return to this biome in the winter, you wouldnot see much of the wildlife you are now observing. One reasonis that many of the bird species migrate to warmer areas. Some ofthe mammals enter a low-energy state similar to sleep calledhibernation. During hibernation an animal relies on fat it hasstored in its body.

wfe~ What are deciduous trees?

Boreal Forest BiomesNow the expedition heads north into a colder climate. The expe-dition leaders claim they can identify the next biome, a borealforest, by its smell. When you arrive, you catch a whiff of thespruce and fir trees that blanket the hillsides. Feeling the chillyearly fall air, you pull a jacket and hat out of your bag.

This forest contains coniferous trees (koh NIF ur us), that pro-duce their seeds in cones and have leaves shaped like needles. Theboreal forest is sometimes referred to by its Russian name, thetaiga (TY guh). Winters in these forests are very cold. The yearly

InferringObserve themap on the facing pageshowing the locations ofdeciduous and boreal forests.How do they compare? Canyou suggest a reason why noboreal forests are shown in theSouthern Hemisphere?

Figure 20 Common organisms ofthe boreal forest include moose likethis one in Alaska's Denali NationalPark, and porcupines.