SECTION 2 Forest Biomes
SECTION 2Forest BiomesObjectives왘 List three characteristics of tropicalrain forests.왘 Name and describe the mainlayers of a tropical rain forest.왘 Describe one plant in a temperatedeciduous forest and an adaptation that helps the plant survive.왘 Describe one adaptation that mayhelp an animal survive in the taiga.왘 Name two threats to the world’sforest biomes.Key Termstropical rain forestemergent layercanopyepiphyteunderstorytemperate rain foresttemperate deciduous foresttaigaThe air is hot and heavy with humidity. You walk through theshade of the tropical rain forest, step carefully over tangles ofroots and vines, and brush past enormous leaves. Life is allaround you, but you see little vegetation on the forest floor. Birdscall, and monkeys chatter from above.Tropical Rain ForestsOf all the biomes in the world, forest biomes are the most widespread and the most diverse. The large trees of forests need a lot ofwater, so forests exist where temperatures are mild to hot andwhere rainfall is plentiful. Tropical, temperate, and coniferousforests are the three main forest biomes of the world.Tropical rain forests are located in a belt around the Earthnear the equator, as shown in Figure 5. They help regulate worldclimate and play vital roles in the nitrogen, oxygen, and carboncycles. Tropical rain forests are always humid and warm and getabout 200 to 450 cm of rain a year. Because they are near theequator, tropical rain forests get strong sunlight year-round andmaintain a relatively constant temperature year-round. This climateis ideal for a wide variety of plants and animals, as shown inFigure 6. The warm, wet conditions also nourish more species ofplants than any other biome does. While one hectare (10,000 m2)of temperate forest usually contains a few species of trees, the samearea of tropical rain forest may contain more than 100 species.왘 Glasswing butterflies live in therain forests of Costa Rica.왘 The Rafflessia keithii flowergrows in the rain forestsof Borneo.146Copyright by Holt, Rinehart and Winston. All rights reserved.
Nutrients in Tropical Rain Forests You might think that thediverse plant life grows on rich soil, but it does not. Most nutrients are within plants, not within soil. Rapid decay of plants andanimals occurs with the help of decomposers, organisms thatbreak down dead organisms. Decomposers on the rain-forestfloor break down dead organisms and return nutrients to thesoil, but plants quickly absorb the nutrients. Some trees in thetropical rain forest support fungi that feed on dead organic matter on the rain-forest floor. In this relationship, fungi transfer thenutrients from the dead organic matter directly to the tree.Nutrients from dead organic matter are removed so efficientlythat runoff from rain forests is often as pure as distilled water.Most tropical soils that are cleared of plants for agriculture lacknutrients and cannot support crops for more than a few years.Many of the trees form above-ground roots called buttresses orbraces that grow sideways from the trees and provide extra support to the tree in the thin 405–50Temperature ( C)Precipitation (cm)Tropical Rain Forest(Limon, Costa Rica)–600J F MAM J J A S ONDMonthsFigure 5 왘 The world’s tropicalrain forests have heavy, year-roundrainfall and fairly constant, warmtemperatures.Figure 6 왘 Species of Tropical왘 The rain forests that blanket the Andes Mountainsof Ecuador are always humid and warm.Rain Forests왘 These mountain gorillas live in therain forests of Rwanda.왘 Scarlet macaws live in the trees of rain forests of Peru.Copyright by Holt, Rinehart and Winston. All rights reserved.Section 2 Forest Biomes 147
wercanopyUnderstoryDenseshadeFigure 7 왘 The plants in tropical rainforests form distinct layers. Theplants in each layer are adapted to aparticular level of light. The tallertrees absorb the most light, while theplants near the forest floor areadapted to growing in the shade.Connection toChemistryMedicines from Plants Manyof the medicines we use comefrom plants native to tropical rainforests. Chemists extract and testchemicals found in plants to determine if the chemicals can cure orfight diseases. Rosy periwinkle, aplant that grows in the tropicalrain forests of Madagascar, is thesource of two medicines, vinblastine and vincristine. Vinblastine isused to treat Hodgkin’s disease, atype of cancer, and vincristine isused to treat childhood leukemia.148 Chapter 6 BiomesLayers of the Rain Forest In tropical rain forests, different typesof plants grow in different layers, as shown in Figure 7. The fourmain layers above the forest floor are the emergent layer, theupper canopy, the lower canopy, and the understory. The top layeris called the emergent layer. This layer consists of the tallest trees,which reach heights of 60 to 70 m. The trunks of trees this tallcan measure up to 5 m around. Trees in the emergent layer growand emerge into direct sunlight. Animals such as eagles, bats,monkeys, and snakes live in the emergent layer.The next layer, considered the primary layer of the rain forest,is called the canopy. Trees in the canopy can grow more than30 m tall. The tall trees form a dense layer that absorbs up to95 percent of the sunlight. The canopy can be split into an uppercanopy and a lower canopy. The lower canopy receives less lightthan the upper canopy does. Plants called epiphytes, such as theorchid in Figure 8, use the entire surface of a tree as a place tolive. Epiphytes grow on tall trees for support and grow high in thecanopy, where their leaves can reach the sunlight needed for photosynthesis. Growing on tall trees also allows them to absorb thewater and nutrients that run down the tree after it rains. Mostanimals that live in the rain forest live in the canopy because theydepend on the abundant flowers and fruits that grow there.Below the canopy, very little light reaches the next layer,called the understory. Trees and shrubs adapted to shade grow inthe understory. Most plants in the understory do not grow morethan 3.5 m tall. Herbs with large, flat leaves that grow on theforest floor capture the small amount of sunlight that penetratesthe understory. These plants must be able to grow in the darkerspots. When fallen trees create an opening in the canopy, treeseedlings that are adapted to grow quickly compete with otherseedlings on the forest floor for sunlight.Copyright by Holt, Rinehart and Winston. All rights reserved.
Species Diversity in Rain Forests The tropical rain forest is thebiome with the greatest amount of species diversity. The diversityof rain-forest vegetation has led to the evolution of a diverse community of animals. Most rain-forest animals are specialists that usespecific resources in particular ways to avoid competition. Somerain-forest animals have amazing adaptations for capturing prey,and other animals have adaptations that they use to escape predators. For example, the collared anteater in Figure 8 uses its longtongue to reach insects in small cracks and holes where other animals cannot reach. The wreathed hornbill (shown below) uses itsstrong, curved beak to crack open nutshells. Insects, such as theCosta Rican mantis in Figure 8, use camouflage to avoid predatorsand may be shaped like leaves or twigs.EcofactA Little Land, A Lot of SpeciesTropical rain forests cover less than7 percent of Earth’s land surfacebut contain at least 50 percent ofall the plant and animal species inthe world.Figure 8 왘 Examples of plantand animal adaptations in thetropical rain forest includethelong tongue of a collared anteater,the strong, curved beak of awreathed hornbill,the shape of aCosta Rican mantis, andan orchidattached to a tall tree.Copyright by Holt, Rinehart and Winston. All rights reserved.149
www.scilinks.orgTopic: Threats toRain ForestsSciLinks code: HE4112Threats to Rain Forests Tropical rain forests once covered about20 percent of Earth’s surface. Today, they cover only about 7 percent. Every minute of every day, 100 acres of tropical rain forestare cleared for logging operations, agriculture, or oil exploration.Habitat destruction occurs when land inhabited by an organismis destroyed or altered. If the habitat that an organism dependson is destroyed, the organism is at risk of disappearing.Animals and plants are not the only organisms that live in rainforests. An estimated 50 million native peoples live in tropicalrain forests. These native peoples are also threatened by habitatdestruction. Because they obtain nearly everything they need fromthe forest, the loss of their habitat could be devastating. This lossof habitat may force them to leave their homes and move intocities. This drastic change of lifestyle may also cause the nativepeoples to lose their culture and traditions along the way.Plants and animals that live in rain forests are also threatenedby trading. Many plant species found only in tropical rain forestsare valuable and marketable to industries. Animals are threatenedby exotic-pet trading. Some exotic-pet traders illegally trap animals, such as parrots, and sell them in pet stores at high prices.Deforestation,Climate, and FloodsA plant absorbs water from the soilthrough its roots and transports thewater to its stems and leaves. Waterthen evaporates from pores in plantleaves into the atmosphere througha process called transpiration. Alarge tree may transpire as much asfive tons of water on a hot day.Water absorbs heat when it evaporates. Therefore, the temperature ismuch cooler under a tree on a hotday than under a wood or brickshelter. Trees that provide shadearound homes keep homes muchcooler in the summer.When rain falls on a forest, muchof the rain is absorbed by plant rootsand transpired into the air as watervapor. Water vapor forms rain clouds.Much of this water will fall as rainsomewhere downwind from the forest. Because of the role trees play in150 Chapter 6 Biomestranspiration, deforestation, the clearing of trees, can change the climate.If a forest is cut down or replaced bysmaller plants, much of the rainfall isnot absorbed by plants. Instead, therain runs off the soil and causesflooding as well as soil erosion. So,the climate downwind from the forest becomes drier.Deforestation led to the disastrous flooding of the Yangtze Riverin China in 1998. More than 2,000people died in the floods, and atleast 13 million people had to leavetheir homes. When the YangtzeRiver flooded, the water pouredinto a flood plain where over 400million people lived. It is estimatedthat 85 percent of the forest in theYangtze River basin has been cutdown. The millions of tons of waterthat these trees once absorbed now왘 A man makes his way past floodedbuildings in his street on a makeshiftraft after the Yangtze River floodedin July 1998. Water of the YangtzeRiver reached record-high levels.flows freely down the river andspreads across fields and into townsduring the seasonal monsoon rains.Deforestation has also causedterrible floods in places such asBangladesh. The Ganges River riseshigh in the Himalaya Mountainsand flows through Bangladesh.Deforestation of the HimalayaCopyright by Holt, Rinehart and Winston. All rights reserved.
Temperate ForestsTemperate rain forest occurs in North America, Australia, andNew Zealand. Temperate rain forests have large amounts of precipitation, high humidity, and moderate temperatures. The PacificNorthwest shown in Figure 9, houses North America’s only temperate rain forest, where tree branches are draped with mossesand tree trunks are covered in lichens. The forest floor is blanketed with lush ferns. Evergreen trees that are 90 m tall, such asthe Sitka spruce and the Douglas fir, dominate the forest. Otherlarge trees, such as western hemlock, Pacific silver fir, and redwood, can also be found in temperate rain forests.Even though the temperate rain forest of the PacificNorthwest is located north of most other rain forests, it stillmaintains a moderate temperature year-round. The temperaterain forest also rarely freezes because the nearby Pacific Oceanwaters keep temperatures mild by blowing cool ocean wind overthe forest. As this ocean wind meets the coastal OlympicMountains, a large amount of rainfall is produced. This rainfallkeeps the temperate rain forest cool and moist.Figure 9 왘 The only temperate rainforest in North America is located inthe Pacific Northwest, as shownabove in Olympic National Park inWashington State.never been flooded before. Thetownspeople claimed that authoritieshad permitted developers to coverthe hills with homes. These developers cut down most of the trees andcovered much of the land withasphalt. After heavy rains, the waterwas no longer absorbed by trees andsoil, so the water flowed down thehills and flooded the town.CRITICAL THINKING왘 Deforestation reduces the amount of water that is absorbed by plantsafter it rains. The more trees that are cleared from a forest, the more likelya flood will occur in that area.Mountains left few trees to stop thewater flowing down the mountain.So, most of the water flows into theriver when it rains. Heavy rains haveeroded and carried away so muchsoil from the slopes of the mountains that the soil has formed a newisland in the Bay of Bengal, which isoff the coast of Bangladesh.People are beginning to understand the connection between deforestation and floods. People heldprotests in northern Italy in 2000after floods covered a town that hadCopyright by Holt, Rinehart and Winston. All rights reserved.1. Identifying RelationshipsHow might the floods in China andother countries affect the overallclimate of the Earth?2. Analyzing a ViewpointImagine that you are a city councilmember and must vote on whetherto clear a forest so that a mall canbe built. List the pros and cons ofeach viewpoint. After reviewingyour list, how would you vote?Explain your answer.Section 2 Forest Biomes 151
�500Temperature ( C)Precipitation (cm)Temperate Deciduous Forest(Stuttgart, Germany)–60J F MAM J J A S ONDMonthsFigure 10 왘 The difference betweensummer and winter temperaturesin temperate deciduous forests isextreme.www.scilinks.orgTopic: TemperateDeciduous ForestsSciLinks code: HE4110Figure 11 왘 The change of seasonsin a temperate deciduous forest inMichigan is shown below.152Temperate Deciduous ForestsIf you walk through a North American deciduous forest in thefall, you will immerse yourself in color. Leaves in every shade oforange, red, and yellow crackle beneath your feet. Most birdshave flown south. The forest is quieter than it was in the summer.You see mostly chipmunks and squirrels gathering and storing thefood they will need during the long, cold winter.In temperate deciduous forests, trees drop their broad, flatleaves each fall. These forests once dominated vast regions of theEarth, including parts of North America, Europe, and Asia.Today, temperate deciduous forests are generally located between30 and 50 north latitude, as shown in Figure 10. The range oftemperatures in a temperate deciduous forest can be extreme, andthe growing season lasts for only four to six months. Summertemperatures can soar to 35 C. Winter temperatures often fallbelow freezing, so little water is available for plants. Temperatures vary due to a change of seasons, as shown in Figure 11.Temperate deciduous forests are moist. They receive 75 to 125 cmof precipitation annually. The rain and snow help decomposedead organic matter, such as fallen leaves, which in turn contributes to the rich, deep soils of temperate deciduous forests.Plants of Temperate Deciduous Forests Like the plants of tropical rain forests, the plants in deciduous forests grow in layers.Tall trees, such as maple, oak, and birch, dominate the forestcanopy. Small trees and shrubs cover the understory. Because theforest floor in a deciduous forest gets more light than that of arain forest does, more plants such as ferns, herbs, and mossesgrow in a deciduous forest.Copyright by Holt, Rinehartand Winston. All rights reserved.
Temperate-forest plants are adapted to survive seasonalchanges. In the fall, most deciduous trees begin to shed theirleaves. In the winter, moisture in the soil changes to ice, whichcauses the remaining leaves to fall to the ground. Also, herbseeds, bulbs, and rhizomes, which are underground stems,become dormant in the ground and are insulated by the soil,leaf litter, and snow. In the spring, when sunlight increasesand temperatures rise, trees grow new leaves, seeds germinate, and rhizomes and roots grow new shoots and stems.Animals of Temperate Deciduous Forests The animals oftemperate deciduous forests are adapted to use the forestplants for food and shelter. Squirrels eat the nuts, seeds,and fruits in the treetops. Bears feast on the leaves andberries of forest plants. Grasshoppers, such as the oneshown in Figure 12, eat almost all types of vegetationfound throughout the forest, while deer and other herbivores nibble leaves from trees and shrubs.Many birds nest in the relative safety of the canopy.Most of these birds are migratory. Because the birds cannot survive the harsh winters, each fall they fly south forwarmer weather and for more available food. Eachspring, they return north to nest and feed. Animals thatdo not migrate use various strategies for surviving thewinter. For example, mammals and insects reduce theiractivity so that they do not need as much food for energy.Figure 12 왘 Grasshoppers, wood-peckers, and deer are among manyanimals that live in the temperatedeciduous forest.TaigaFigure 13 왘 The taiga has long, coldwinters and small amounts of precipitation, as shown in the 15–3010–405–500Temperature ( C)Taiga(Edmonton, Canada)Precipitation (cm)The taiga is the northern coniferous forest that stretches in a broadband across the Northern Hemisphere just below the Arctic Circle.As shown in Figure 13, winters are long (6 to 10 months) and haveaverage temperatures that are below freezing and that often fall to–20 C. In the taiga, the forest floor is dark and has little vegetation.Many trees seem like straight, dead shafts of bark and wood—untilyou look up and see their green tops. The growing season in thetaiga may be as short as 50 days depending on latitude. Plantgrowth is most abundant during the summer months because ofnearly constant daylight and larger amounts of precipitation.–60J F MAM J J A S ONDMonthsCopyright by Holt, Rinehart and Winston. All rights reserved.Section 2 Forest Biomes 153
Plants of the Taiga A conifer is a tree that has seeds thatdevelop in cones. Most conifers do not shed their needle-shapedleaves, which help them survive harsh winters. The leaves’ narrow shape and waxy coating retain water for the tree when themoisture in the ground is frozen. As shown in Figure 14, aconifer’s pointed shape also helps the tree shed snow to the groundso that it does not become weighed down.Conifer needles contain substances that make the soil acidicwhen the needles fall to the ground. Most plants cannot grow inacidic soil, which is one reason the forest floor of thetaiga has few plants. In addition, soil forms slowlyin the taiga because the climate and acidity of thefallen leaves slow decomposition.Figure 14 왘 The taiga has cold winter temperatures, a small amount ofannual precipitation, and coniferoustrees. The seeds of conifers are protected inside tough cones like theone above. Also, the narrow shapeand waxy coating of conifer needleshelp the tree retain water.Animals of the Taiga The taiga has many lakesand swamps that in summer attract birds thatfeed on insects, fish, or other aquatic organisms.Many birds migrate south to avoid winter in thetaiga. Some year-round residents, such as shrews androdents, may burrow underground during the winter, becausethe deep snow cover insulates the ground. Moose and snowshoehares eat any vegetation they can find. As shown in Figure 15, someanimals, such as snowshoe hares, have adapted to avoid predationby lynxes, wolves, and foxes by shedding their brown summer furand growing white fur that camouflages them in the winter snow.Figure 15 왘 In the taiga, a snowshoehare’s fur changes color according tothe seasons to help camouflage theanimal from predators.SECTION 2Review1. List three characteristics of tropical rain forests.CRITICAL THINKING2. Name the main layers of a tropical rain forest. Whatkinds of plants grow in each layer?5. Evaluating Information Which would be bettersuited for agricultural development: the soil of a tropical rain forest or the soil of a temperate deciduousforest? Explain your answer.3. Describe two ways in which the forest biomes of theworld are being threatened.4. Describe how a plant survives the change of seasons in a temperate deciduous forest. Write a shortparagraph to explain your answer. WRITING SKILLS154 Chapter 6 Biomes6. Identifying Relationships How does a snowshoehare avoid predation by other animals during thewinter in a taiga biome? How might this affect theanimal that depends on the snowshoe hare for food?Copyright by Holt, Rinehart and Winston. All rights reserved.
biome with the greatest amount of species diversity. The diversity of rain-forest vegetation has led to the evolution of a diverse com-munity of animals. Most rain-forest animals are specialists that use specific resources in particular ways to avoid competition. Some rain-forest animals have
There are many different biomes on Earth. The figure below shows a map of the major land biomes. Land biomes are biomes that are found on land. This map shows some of the major land biomes on Earth. BEFORE YOU READ National Science Education Standards LS 1a, 3a, 3c, 3d, 4b, 4c, 4d, 5a, 5b ST
Equatorial and tropical forest biome 4. Midlatitude broadleaf and mixed forest biome 5. Needleleaf and montane forest biome . FOREST (mainly trees) GRASSLAND (mainly grasses) . (dry conditions, leathery scrub vegetation) Types of terrestrial biomes: Global terrestrial biomes. Source: Christopherson, 2012, p. 596-657. Global terrestrial
4.4 Biomes . BiomesLesson Overview The Major Biomes What abiotic and biotic factors characterize biomes? Biomes are described in terms of abiotic factors like climate and soil type, and biotic factors like plant and animal life. BiomesLesson Overview The Major Biomes
(A) boreal forest º temperate forest º tropical rain forest º tundra (B) boreal forest º temperate forest º tundra º tropical rain forest (C) tundra º boreal forest º temperate forest º tropical rain forest (D) tundra º boreal forest º tropical rain forest º temperate forest 22. Based on the
Chapter 4: Ecosystems & Communities Section 4: Biomes Biomes}Biome: large region characterized by a specific type of climate and certain types of plants and communities. Biomes are described in terms of abiotic factors like climate and soil type, and biotic factors like plant and animal life Terrestrial Biomes Tropical Rain Forest (Page 112)
Biomes Section 1 Biomes and Vegetation Biomes are described by their vegetation because plants that grow in an area determine the other organisms that can live there. Plants in a particular biome have characteristics, specialized structures, or adaptations that allow the plants to survive in that biome.
biomes are determined mainly by climate. Terrestrial biomes include tundras, temperate forests and grasslands, chaparral, temperate and tropical deserts, and tropical forests and grasslands. Terrestrial Biomes and Climate Climate is the average weather in an area over a long period of time. Weather refers to the conditions of the
12. What is a biome? Answer: A biome is a large community of plants and animals that occupies a distinct region. Biomes on the land are defined by their climate and dominant vegetation. The two biomes in the virtual field trip are desert and temperate rainforest but other biomes include grasslands, tropical
