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The number of insect species in tropical rain forests is not known, but has been estimated to be in the millions. These in turn feed many bird species, which feed other animals. Although tropical rain forests cover only a small part of the planet, they probably contain more species of plants and animals than all the other land biomes combined. Temperate Rain Forests The land along the northwestern coast of the United States resembles a tropical rain forest in some ways. This region receives more than 300 centimeters of rain a year. Huge trees grow there, including cedars, redwoods, and Douglas firs. However, it is difficult to classify this region. It is too far north and too cool to be a tropical rain forest. Instead many ecologists refer to this ecosystem as a temperate rain forest. The term temperate means having moderate temperatures. Desert Biomes Figure 17 Desert organisms have adaptations that enable them to live in the harsh conditions of their biome. For example, this shovelsnouted lizard "dances" to avoid burning its feet on the hot sand dunes of the Namib Desert in Africa. Making Generalizations Describe the climate conditions of a typical desert. The next stop on your expedition is a desert. It couldn't be more different from the tropical rain forest you just left. You step off the bus into the searing summer heat. At midday, you cannot even walk into the desert-the sand feels as hot as the hot water that comes from your bathroom faucet at home. A desert is an area that receives less than 25 centimeters of rain per year. The amount of evaporation in a desert is greater than the amount of precipitation. Some of the driest deserts may not receive any rain at all in a year! Deserts often also 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, even experiencing freezing temperatures in the winter. The organisms that live in the desert are adapted to the lack of rain and to the extreme temperatures. For example, the trunk of a saguaro cactus has folds that work like the pleats in an accordion. The trunk of the cactus expands to hold more water when it is raining. Many desert animals are most active at night when the temperatures are cooler. A gila monster, for instance, spends much of its time in a cool underground burrow. It may go for weeks without coming up to the surface of the desert. wf e~ What are some adaptations that help an organism to live in the desert? Grassland Biomes The next stop on the expedition is a grassland called a prairie. The temperature here is much more comfortable than that in the desert. The breeze carries the scent of soil warmed by the sun. This rich soil supports grass as tall as you and your classmates. Sparrows flit among the grass stems, looking for their next meal. Startled by your approach, a rabbit quickly bounds away. Like other grasslands located in the middle latitudes, this prairie receives more rain than deserts, but not enough for many trees to grow. A grassland receives between 25 and 75 centimeters of rain each year, and is typically populated by grasses and other nonwoody plants. Grasslands that are located closer to the equator than prairies, called savannas, receive as much as 120 centimeteFS of Til • -.s Desert Survival gUsea Uhand lens to carefully observe a small potted cactus. Be careful of the spines! With a pair of scissors, carefully snip a small piece from the tip of the cactus. Observe the inside of the plant. Note any characteristics that seem different from those of other plants. Observing How is the inside of the cactus different from the outside? Suggest how the features you observe might be related to its desert habitat. Figure 18 Migrating wildebeest make their way across a vast Kenyan savanna. Chapter 2 E. 65 Forest Biomes • Deciduous forest • Boreal forest Figure 19 This Michigan forest in autumn is a beautiful example of a deciduous forest. The closeup shows a red fox, a common resident of North American deciduous forests. Comparing and Contrasting How do deciduous forests differ from rain forests? 66+E rain each year. Scattered shrubs and small trees grow on savannas along with the grass. Grasslands are home to many of the largest animals on Earth-herbivores such as bison, antelopes, zebras, rhinoceros, giraffes, and kangaroos. Grazing by these large herbivores helps to maintain the grasslands. They keep young trees and bushes from sprouting and competing with the grass for water and sunlight. Deciduous Forest Biomes Your trip to the next biome takes you to another forest. It is now late summer. Cool mornings here give way to warm days. Several members of the expedition are busy recording the numerous plant species. Others are looking through their binoculars, trying to identify the songbirds in the trees. You step carefully to avoid a small salamander on the forest floor. Chipmunks chatter at all the disturbance. You are now visiting the deciduous forest biome. The trees found in this forest, called deciduous trees (dee SIJ 00 us), shed their leaves and grow new ones each year. Oaks and maples are examples of d~iduous trees. Deciduous forests receive enough rain to support the growth of trees and other plants, at least 50 centimeters per year. Temperatures vary during the year. The growing season usually lasts five to six months. As in the rain forest, different plants grow to different heights, ranging from a canopy of tall trees to small ferns and mosses on the forest floor. The variety of plants in the forest creates many different habitats. You and your classmates note that different species of birds live at each level, eating the insects and fruits that live and grow there. You observe opossums, mice, and a skunk looking for food in the thick layer of damp leaves on the ground. Other common North 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 would not see much of the wildlife you are now observing. One reason is that many of the bird species migrate to warmer areas. Some of the mammals enter a low-energy state similar to sleep called hibernation. During hibernation an animal relies on fat it has stored in its body. wf e~ Inferring Observe the map on the facing page showing the locations of deciduous and boreal forests. How do they compare? Can you suggest a reason why no boreal forests are shown in the Southern Hemisphere? What are deciduous trees? Boreal Forest Biomes Now the expedition heads north into a colder climate. The expedition leaders claim they can identify the next biome, a boreal forest, by its smell. When you arrive, you catch a whiff of the spruce and fir trees that blanket the hillsides. Feeling the chilly early fall air, you pull a jacket and hat out of your bag. This forest contains coniferous trees (koh NIF ur us), that produce their seeds in cones and have leaves shaped like needles. The boreal forest is sometimes referred to by its Russian name, the taiga (TY guh). Winters in these forests are very cold. The yearly Figure 20 Common organisms of the boreal forest include moose like this one in Alaska's Denali National Park, and porcupines.