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Terrestrial Biomes
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C ONCEPT
Concept 1. Terrestrial Biomes
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Terrestrial Biomes
Lesson Objectives
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State how terrestrial biomes are classified and distributed around the globe.
Outline abiotic and biotic factors in tundra and boreal forest biomes.
Describe climatic factors and organisms of temperate zone biomes.
List abiotic factors in deserts and adaptations of desert organisms.
Identify abiotic factors and organisms in tropical biomes.
Introduction
Terrestrial biomes include all land areas on Earth where organisms live. The major biomes cover large regions and
are found on more than one continent. They are generally classified on the basis of climatic factors and the types of
plants that are the primary producers.
Classification of Terrestrial Biomes
Scientists have created several different systems for classifying terrestrial biomes. Biomes in most classification
systems include tundra, boreal forest, temperate forest, temperate grassland, chaparral, tropical forest, tropical
grassland, and desert. The worldwide distribution of these biomes is shown in Figure 1.
FIGURE 1.1
Distribution of Earth’s major terrestrial
biomes.
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The distribution of biomes shown in Figure 1 reflects global patterns of temperature and moisture. It also reflects
conditions in earlier times. Many areas have been disturbed by human actions, some more so than others. For
example, most tundra biomes have been changed very little by human actions, but many forests have been completely
cleared. Some biomes, including tropical rainforests, cannot be replaced once they have been destroyed. Figure 2
summarizes important features of most of the biomes shown in Figure 1. Refer to both figures as you read about
these terrestrial biomes throughout this lesson.
FIGURE 1.2
These biomes are described more fully in
the text. Refer to Figure 1 to see where
each biome is found.
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Concept 1. Terrestrial Biomes
Arctic and Subarctic Biomes
Artic and subarctic biomes are found near the north and south poles or at high altitudes in other climate zones. The
biomes include tundra and boreal forests. Both have cold, dry climates and poor soil. They can support only limited
plant growth and have low biodiversity.
Tundra
Tundra is an arctic biome where it is too cold for trees to grow. Outside of the polar ice caps, tundra has the coldest
temperatures on Earth. There are two types of tundra: arctic tundra, which is also found in Antarctica, and alpine
tundra, which is found only at high altitudes.
• Arctic tundra occurs north of the arctic circle and south of the antarctic circle. It covers much of Alaska and
vast areas of northern Canada and Russia. It is also found along the northern coast of Antarctica.
• Alpine tundra occurs in mountains around the world at any latitude, but only above the tree line. The tree
line is the edge of the zone at which trees are able to survive. Alpine tundra is found in the Rocky Mountains
in the United States and in several other mountain ranges around the world.
Both types of tundra receive very low precipitation, but little of it evaporates because of the cold. Arctic tundra has
permafrost, which is soil that is frozen year-round. The top layer of soil thaws in the summer, but deeper layers do
not. As a result, water cannot soak into the ground. This leaves the soil soggy and creates many bogs, lakes, and
streams. Alpine tundra does not have permafrost, except at very high altitudes. Therefore, alpine tundra soil tends
to be dry rather than soggy.
Global warming poses a serious threat to Arctic tundra biomes because it is causing the permafrost to melt. When
permafrost melts, it not only changes the tundra. It also releases large amounts of methane and carbon dioxide into
the atmosphere. Both are greenhouse gases, which contribute to greater global warming.
The most common vegetation in tundra is mosses and lichens. They can grow in very little soil and become dormant
during the winter. Tundra is too cold for amphibians or reptiles, which cannot regulate their own body heat. Insects
such as mosquitoes can survive the winter as pupae and are very numerous in summer. In addition, many species of
birds and large herds of caribou migrate to arctic tundra each summer. However, few birds and mammals live there
year-round. Those that remain have adapted to the extreme cold. Polar bears are an example. They have very thick
fur to insulate them from the cold. In alpine tundra, animals must adapt to rugged terrain as well as to cold. Alpine
animals include mountain goats, which not only have wool to keep them warm but are also sure-footed and agile.
Boreal Forests
A boreal forest is a subarctic biome covered with conifers. Conifers are cone-bearing, needle-leaved evergreen trees
such as spruces. Boreal forests are found only in the northern hemisphere. They occur just south of the arctic circle
in Alaska, Canada, northern Europe, and Russia (where they are called taiga). They also occur in extreme northern
regions of Minnesota, New York State, New Hampshire, and Maine.
Boreal forests have harsh continental climates, with very cold winters and relatively warm summers. The growing
season is also short. Precipitation is quite low, but there is little evaporation. Most of the precipitation falls in the
summer when plants are growing, so there is enough moisture for dense plant growth. A thick carpet of evergreen
needles on the forest floor causes the soil to be too acidic for most other plants.
Conifers have adapted to the difficult conditions in several ways. They have shallow roots that suit them for the thin
soil. They have needles instead of leaves, which reduce water loss during the long, dry winters. The needles are
also very dark green in color, which maximizes absorption of sunlight for photosynthesis. Although boreal forests
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are dense with conifers, there are only a few different species of trees. Vegetation on the forest floor consists mostly
of mosses and lichens. Animals found in boreal forests include insects, birds, and mammals such as rabbits, foxes,
and brown bears. Caribou also spend their winters there. Like tundra, the boreal forest is too cold for amphibians or
reptiles.
Temperate Biomes
Temperate biomes cover most of the continental United States and Europe. They also cover large parts of Asia.
Types of temperate biomes include forests, grasslands, and chaparral.
Temperate Forests
There are two types of temperate forests: temperate deciduous forests and temperate rainforests. Both types have
a temperate climate and good soil. A temperate climate is a moderate climate that is neither extremely hot nor
extremely cold. A temperate climate can be either continental or coastal. Continental temperate climates are found
inland, and they tend to have cold winters, hot summers, and moderate precipitation. Coastal temperate climates are
found near the ocean, and they tend to have mild winters, cool summers, and high precipitation.
• Temperate deciduous forests are found in areas with continental temperate climates, such as the eastern
United States and Canada and throughout much of Europe. These forests consist mainly of deciduous trees,
such as maples and oaks, which lose their leaves in the fall. There are many other species of plants as well.
Animals include insects, amphibians, reptiles, and birds. Mammals are also common, including rabbits and
wolves.
• Temperate rainforests are found in areas with coastal temperate climates, such as the northwestern coast
of North America and certain coastal regions of other continents. These forests consist mainly of evergreen
trees, such as hemlocks and firs. Mosses, lichens, and ferns grow on the forest floor. There are also many
epiphytic plants. Animals include insects, amphibians, reptiles, and birds. There are also many mammals,
such as squirrels and deer.
Epiphytes are plants that grow on other plants. They use the other plants for support, not nutrients, and generally
do not harm the plants they grow on. They grow high in the branches of trees where there is more sunlight available
for photosynthesis.
Temperate Grasslands
Temperate grasslands are temperate biomes that consist mainly of grasses. They are found in the midwestern
region of North America and in inland areas of most other continents. The climate is continental, and precipitation
is relatively low. However, the majority of the precipitation falls during the growing season when plants need it the
most.
Biomes are often referred to by local names. For example, a temperate grassland biome is known as prairie in North
America, outback in Australia, pampa in South America, and steppe in central Asia. Can you find each of these
temperate grasslands on the map in Figure 1?
The soil of temperate grasslands is the richest, deepest soil on Earth. It is densely covered with thick grasses that
decompose to add large amounts of organic matter and nutrients to the soil. Grasses also have thick mats of roots
that hold the soil in place and prevent erosion. The low rainfall does not leach many nutrients from the soil, but it
does lead to frequent fires. The fires help prevent woody vegetation from moving in if a grassland is disturbed. This
is because grasses can grow back after a fire, whereas most woody plants cannot.
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Concept 1. Terrestrial Biomes
The rich, deep soil supports high productivity. This is why the temperate grassland of the US midwest is known as the
Breadbasket of America. Grass plants are closely spaced and can support many herbivore consumers. These range
from grasshoppers to deer. Many worms and other invertebrates (animals without a backbone) consume organic
matter in the soil. Grassland animals also include carnivores such as foxes and coyotes.
Chaparral
Chaparral is a shrub forest biome dominated by densely-growing evergreen shrubs or small trees, such as scrub
oak. There are few other species of plants. Chaparral is found mainly in central and southern California and around
the Mediterranean Sea. The climate, called a Mediterranean climate, has mild wet winters and hot dry summers.
Fires are frequent because of the summer dryness, and the soil is relatively poor.
The majority of chaparral trees and plants are adapted to the dry summers. For example:
• Trees are short, which reduces their need for water.
• Many plants are dormant during the dry season, which also reduces water needs.
• The leaves of some plants have waxy coatings, which reduce water loss.
Most chaparral plants are adapted to frequent fires, as well. For example:
• Many plants can grow back quickly from the roots after burning to the ground.
• Some plants produce seeds that need fire in order to germinate.
• Many plants have thick underground stems that can survive fires.
The densely growing trees make it difficult for very large animals to penetrate the chaparral, so most chaparral
animals are small. They include insects, birds, reptiles, and rodents. The largest animals are deer, which browse on
the leaves of chaparral trees.
Deserts
A desert is a biome that receives no more than 25 centimeters (10 inches) of precipitation per year. Deserts are
found in both temperate and tropical areas. The largest deserts are found at about 30° north or south latitude due
to the dry air masses over these latitudes. Deserts also occur in rain shadows. A rain shadow is a dry region on the
leeward side of a mountain range (see Lesson 16.1). Examples of rain shadow deserts include Death Valley and the
Mojave Desert, both partly in California. The dry air in deserts leads to extreme temperature variations from day to
night. Without water vapor in the air, there are no clouds to block sunlight during the day or hold in heat at night.
Desert soil is usually very poor. They tend to be sandy or rocky and lack organic content. Because of the low
precipitation, minerals are not leached out and may become too concentrated for plants to tolerate. Plant cover is
very sparse, so most of the soil is exposed and easily eroded by wind. The occasional rain tends to be brief but heavy,
causing runoff and more erosion.
Most desert plants have evolved adaptations to the extreme dryness. For example:
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Many plants have special water-storing tissues in leaves, stems, or roots.
Some plants have very long taproots that can reach down to the water table.
Some plants have wide-spreading roots that can absorb water over a large area.
Plants may have small, spiny leaves that help reduce water loss.
Most desert animals have adaptations to the extreme heat and bright sunlight. For example:
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• Many small animals stay underground in burrows during the day and come out only at night.
• Most animals that are active in daytime spend as much time as possible in the shade of rocks or plants.
• Some animals have very large ears or other appendages, which help them lose heat to the environment, keeping
them cooler.
• Many animals are light in color, which helps them reflect sunlight and stay cooler.
Tropical Biomes
Tropical biomes receive more sunlight than any other biomes on Earth. They also have high temperatures year-round.
In addition to deserts, tropical biomes include forests and grasslands.
Tropical Forests
There are two types of tropical forests: tropical rainforests and tropical dry forests. Both occur near the equator,
so they have plenty of sunlight and warmth year-round. However, they differ in the amount and timing of the
precipitation they receive.
• Tropical rainforests receive more precipitation than any other biome. They are found near the equator in
Central and South America and Africa. The soil is thin and poor, partly because the lush plant growth uses up
nutrients before they can accumulate in the soil. Biodiversity of animals as well as plants is greater than in all
other biomes combined. Most plants are tall, broadleaf evergreen trees. They form a dense canopy over the
forest, so little sunlight reaches the forest floor. The many vines and epiphytes reach sunlight by growing on
trees. Numerous animal species also live in trees, including monkeys, sloths, and leopards.
• Tropical dry forests occur in tropical areas where most of the precipitation falls during a single wet season.
As a result, there is a pronounced dry season. Tropical dry forests are found in parts of Central and South
America, Africa, and India. Trees and other plants are widely spaced because there is not enough water for
denser growth. The plants also have adaptations to help them cope with seasonal drought. For example, many
go dormant during the dry season, which reduces their need for water. Animals that live in tropical dry forests
include arboreal animals such as monkeys and ground-dwelling animals such as rodents.
Tropical Grasslands
Tropical grasslands are tropical biomes with relatively low rainfall where the primary producers are grasses.
Tropical grasslands are found mainly in Africa, where they are called savannas. They have high temperatures
year-round, but relatively low precipitation. Moreover, most of the precipitation falls during a single wet season,
leaving the rest of the year very dry. The soil is also poor.
In addition to grasses, there are scattered clumps of trees in most tropical grasslands. The trees are drought-adapted
species such as acacia, which have narrow leaves that reduce water loss. Acacia trees also have thorns that discourage
browsing by herbivores. Africa savannas are well known for their huge herds of herbivores, including zebra, giraffe,
and wildebeest. They are also well known for their large carnivores—such as lions, cheetahs, and hyenas—that prey
on the herbivores.
Lesson Summary
The concept map below shows how the terrestrial biomes described in this lesson are related.
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Concept 1. Terrestrial Biomes
FIGURE 1.3
Review Questions
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4.
Identify the two types of tundra and where they are found.
Name two temperate biomes and the main type of plant found in each biome.
In which biome are you most likely to find grasses, zebras, and lions?
Assume a new species of lizard has been discovered in the northern hemisphere. It lives in an area of dense
evergreen forest, where mosses and lichens grow on the forest floor. Identify the biome in which the lizard
was found and explain your answer.
5. If you were to design a well-adapted desert animal, what traits would you give it to help it survive in its desert
environment?
6. Compare and contrast two types of temperate forests.
7. If the tropics receive more sunlight year-round than any other biome, why are some plants in tropical rainforests adapted to low levels of sunlight?
Further Reading / Supplemental Links
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Michael Allaby, Grasslands. Chelsea House Publications, 2006.
Michael Allaby, Temperate Forests. Chelsea House Publications, 2006.
Michael Allaby, Tropical Rain Forests. Chelsea House Publications, 2006.
Trevor Day, Taiga. Chelsea House Publications, 2006.
Peter D. Moore, Tundra. Chelsea House Publications, 2006.
Susan L. Woodward, Biomes of Earth: Terrestrial, Aquatic, and Human-Dominated. Greenwood Press, 2003.
http://ag.arizona.edu/OALS/watershed/highlands/chaparral/chsoils.html
http://environment.newscientist.com/article/mg18725124.500.html
http://estrellamountain.edu/faculty/farabee/biobk/BioBookcommecosys.html
http://ridge.icu.ac.jp/gen-ed/biomes.html
http://www.nationalgeographic.com/wildworld/profiles/terrestrial/nt/nt0115.html
http://earthobservatory.nasa.gov/Laboratory/Biome/
http://www.thewildclassroom.com/biomes/index.html
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/B/Biomes.html
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Vocabulary
alpine tundra Tundra biome that occurs in mountains around the world at any latitude, but only above the tree
line.
arctic tundra Tundra biome that occurs north of the arctic circle and south of the antarctic circle.
boreal forest Subarctic biome covered with conifers.
chaparral Temperate biome with a Mediterranean climate that consists mainly of densely-growing evergreen
shrubs such as scrub oak.
desert Temperate or tropical biome that receives no more than 25 centimeters of precipitation per year.
epiphyte Type of plant that grows on other plants for support.
permafrost Frozen soil year-round.
temperate deciduous forest Temperate biome that receives moderate rainfall and consists mainly of deciduous
trees such as maples.
temperate grassland Temperate biome that receives relatively low precipitation and consists mainly of grasses.
temperate rainforest Temperate biome that receives heavy rainfall and consists mainly of evergreen trees such as
hemlocks.
tree line Edge of the zone at which trees are able to survive.
tropical dry forest Tropical biome that receives relatively low rainfall, has a dry season, and consists mainly of
widely spaced, drought-adapted trees.
tropical grassland Tropical biome that receives relatively low rainfall, has a dry season, and consists mainly of
grasses.
tropical rainforest Tropical biome that receives heavy rainfall and consists mainly of tall, broadleaf evergreen
trees.
tundra Arctic biome where it is too cold for trees to grow.
Points to Consider
The land areas where terrestrial biomes are found cover only 30 percent of Earth’s surface. The rest of the surface is
covered by water.
• What types of biomes do you think occur in water?
• How do you think water biomes might be classified?
• What do you think are some of the organisms that live in water biomes?
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