Scientists divide the world into large natural areas called biomes. Desert and rainforest biomes are two that you’ve probably heard of. Each biome is known for certain kinds of plants and animals. But what’s really at the heart of a biome is its climate. How hot or cold is it? How much rain and snow fall every year?

Climate is critical because it determines the types of plants and animals—the ecosystem—that can survive in a biome. Polar bears can’t live in the Sahara Desert. Rain forest trees won’t grow in grasslands or the arctic tundra.

Humans have invented ways to deal with extreme climates and live in every biome. We have air conditioning and water-supply systems, so that we can build cities in deserts. We have underground malls and central heating so we can live in very cold climates. However, some of our human activities are changing the world’s biomes.

Let’s say you flew in a plane from the North Pole to the South Pole, zigzagging over all the continents—and let’s say there were no clouds blocking your view. You would see lots of cities and human developments, but you would also see huge natural areas. Some biomes, such as the tundra (light purple) and taiga (dark green) cover large bands of territory that encircle the Earth and correspond to their latitude. (Designua/ Shutterstock)

The land areas of the Earth can be divided into eight major biomes: tundra, taiga, temperate deciduous forest, temperate grassland (steppe), Mediterranean (chaparral), desert, tropical savanna, and tropical rain forest. But there are no firm rules about the exact number of biomes. In fact, scientists divide the world’s biomes into anywhere from six to seventeen categories. (No one way is better than another—it’s just that some classification systems are more general and others are more specific.)

Tundra

It is crazy cold in the Arctic tundra. It’s so cold that the ground is frozen most of the year, and a deep layer of soil below the surface—called the permafrost—never melts at all. However, for two months during the summer, the temperature rises above freezing. The snow and surface soil melt, creating vast pools of water and bogs.

During this brief summer season, plants have a chance to grow. But due to the harsh conditions and high winds, tundra plants grow very low to the ground. In fact, the tundra is a treeless landscape.

Historically, the tundra covered about 15 percent of the Earth’s land surface. However, scientists estimate that the tundra has shrunk by almost 20 percent over the last 20 years due to climate change. In the southern part of the tundra, parts of the permafrost have melted. Trees now dot the landscape, and animals from warmer climates are moving in.

The tundra is a rocky landscape. Lichen—a combination of fungi and algae—grow on the rocks. Lichens are a favorite food of reindeer that migrate across the tundra in vast herds. During winter, these lichens are one of the only foods available and reindeer will dig through snow to find them. (Incredible Arctic/ Shutterstock)

The arctic fox is well-adapted to life on the tundra. During loooooong arctic winters, it sports a thick, all-white coat for camouflage and warmth. And it often follows polar bears around, eating their leftovers. During summer, the arctic fox’s coat turns brown, and it hunts for its favorite food—lemmings, which are small, furry, short-tailed rodents that also make their home in the tundra. (AdStock RF/ Shutterstock)

Taiga

The taiga is the world’s biggest biome. It covers nearly one-fifth of the Earth’s land surface and stretches across northern Canada and northern Eurasia in an almost unbroken belt for 7,000 miles. The main features of the taiga are its evergreen forests of needle-leafed trees, including pine, spruce, hemlock, and fir. Although this biome is not as harsh as the tundra, all its plants and animals have evolved to survive the taiga’s long, snowy winters.

Taiga trees have many adaptations for surviving harsh winters, a short growing season, and nutrient-poor soil. Their conical shapes allow snow to slip off easily, without weighing down and breaking branches. Their needle-shaped leaves have waxy, protective coatings to lock in moisture. Plus, the needles don’t all fall off in autumn. Keeping the leaves through the winter means taiga trees don’t need to use energy to grow an entire set of new leaves each spring and they can capture energy from the sun throughout the year. (Pi_Lens/ Shutterstock)

Brown bears are top predators of the taiga, hunting everything from deer to fish. They also like berries, nuts, roots, and other vegetation. During the summer, they eat massive amounts of food, sometimes as much as 40 pounds per day. Their bodies convert much of this extra food and store it as fat. In autumn, brown bears dig dens and begin long winter hibernations, during which they live off the stored fat. (Erik Mandre/ Shutterstock)

Tiny but fierce, the seven-inch-high saw-whet owl flies north to the taiga every spring to mate and lay eggs. About half of all North American bird species nest and raise their chicks in the taiga. (Mlorenz/ Shutterstock)

The vast forests of the taiga are being shrunk by massive logging operations. The wood is used to make paper and build houses. When trees are clearcut, the forest habitat is destroyed. Reducing the size of the world’s forests also contributes to global warming. Forests are called “carbon sinks” because they absorb carbon dioxide and help keep the world’s carbon cycle in balance. When too much carbon gas is released into the atmosphere, the climate tends to warm—and that can have serious consequences for humans and ecosystems. (Christopher Kolaczan/ Shutterstock)

Temperate Deciduous Forest

This biome is defined by its four distinct seasons and its forests of trees that drop their leaves in autumn. (The word “deciduous” [dih-SID-yoo-uhss] comes from a Latin word meaning “to fall.”) Located in the eastern United States, all over Europe, Japan, and parts of Russia and China, temperate deciduous forests are home to deer, wolves, hawks and owls, songbirds, and many other species.

Temperate deciduous forests change dramatically with the seasons. During spring, each tree produces thousands of new leaves filled with green chlorophyll. The chlorophyll traps sunlight and converts it into fuel for the tree’s growth. Unlike the trees of the taiga which are evergreens, these trees prepare for winter by breaking down the chlorophyll in their leaves, storing some of the nutrients, and then dropping their leaves. A by-product of the breakdown of the chlorophyll is the exposure of yellow, orange, and red pigments that are normally masked. That means that in fall, the trees in these forests are alight with fiery colors.

An entire tourism industry revolves around “leaf peeping.” In the United States, about $30 billion a year is spent by people traveling to see the fall colors. (Creative Travel Projects/ Shutterstock)

Deciduous forests have at least three layers. The tallest trees make up the canopy. Saplings and shrubs are found in the understory. Ferns, moss, and wildflowers grow on the forest floor. (Natalia Bratslavsky/ Shutterstock)

Although many birds of the temperate deciduous forest head south for the winter, black-capped chickadees stick around. How do they do it? They hide thousands of seeds under tree bark during the fall and eat them throughout the winter. (BGSmith/ Shutterstock)

Tropical Savanna

Tropical savannas are vast grasslands dotted with trees that spread across Africa, northern Australia, and parts of South America and India. With wide open spaces and so much grass to graze on, savannas are home to large herds of plant-eating animals (herbivores). They are also usually home to large predators that stalk the herds. In the African savanna, the plant-eaters include zebras, antelopes, wildebeest, giraffes, elephants, and rhinos. Predators include lions, leopards, cheetahs, and hyenas. In the Australian savanna, kangaroos are the primary plant-eaters.

Many of Africa’s savanna herbivores have long, powerful legs to help them travel long distances and run away from predators. Some, like the ostrich and giraffe, have VERY long legs—and they can even use them to kick predators. In the Australian savanna, kangaroos have a slightly different strategy for getting around: They don’t run, but hop—as far as 30 feet in a single leap and can speed-hop at 35 mph.

The weather in the savanna is warm year-round, and there are basically two seasons—wet and dry. To survive the dry season, many savanna animals must migrate in search of water.

These eastern gray kangaroos are just one of over 40 species of kangaroo-like animals, living in Australia’s savannas—better known as “the bush.” Want to know something strange? While kangaroos still have the hair-trigger ability to leap out of danger and escape the sharp teeth of carnivores, most of the kangaroos’ predators have gone extinct. (Robyn Butler/ Shutterstock)

Every year, 300,000 zebra and 1 million wildebeest in Africa’s Serengeti Plain embark on an extended migration. To find water and green grass, they must cross the Mara River. But the crossing is dangerous, with some animals swept away by strong currents and a few attacked by crocodiles. (GTS Production/ Shutterstock)

These African elephants are on the move in the savanna beneath Africa’s Mount Kilimanjaro. During the rainy season, elephants get about 50 percent of their diet from grasses. In the dry season, they rely more on trees and shrubs for food. (Francois Gagnon/ Shutterstock)

Temperate Grassland

Temperate grasslands include the prairie in North America and the steppes of Europe and Asia. They are characterized by vast stretches of high grasses and wildflowers. Summers are very hot and winters are very cold. These regions are subject to droughts—periods without rain—as well as regular wildfires.

The wildfires are set off by lightning strikes in the dry grasses. The fires prevent trees from growing and they also return nutrients to the soil. Because the soil below the surface doesn’t heat up much during a typical grassland fire, the mat-like roots of the grasses survive and send up shoots the following spring.

Because grasslands have amazingly rich soil, many areas that were once natural grasslands have been taken over for farming.

Before 1800, some 25 million bison roamed America’s grasslands. But the bison were so heavily hunted that by 1900, there were only a few hundred left. With the help of conservationists, bison populations have bounced back a little. Today, a few thousand wild bison live in national parks like Yellowstone. (Martha Marks/ Shutterstock)

Groups of prairie dogs live together in extensive underground burrows, called “towns.” When they come out to eat, one prairie dog stands guard and makes warning whistles if it senses danger. (Henk Bentlage/ Shutterstock)

Once the Saiga antelope roamed the Eurasian steppe in huge herds. In recent years, it has been hunted close to extinction and is now considered a critically endangered species. Its strange-looking nose is almost like a cut-off elephant’s trunk—scientists believe this special nose warms up frigid air before it reaches the Saiga’s lungs in winter and filters out dust in summer. (BBH/ Shutterstock)

Native to the steppes of Eurasia, Przewalski’s horse is the only truly wild horse. This breed has never been ridden or tamed. In the 1970s, it went extinct in the wild, but captive-bred animals were later re-introduced into the steppes. Przewalski’s horse is known for its Mohawk-style mane, short legs, and stocky body. The two horses shown here are rubbing each other’s backs—an activity that biologists call “mutual grooming.” (Anita Huszti/ Shutterstock)

Desert

The desert is the driest biome. Some deserts, such as the Sahara, get less than an inch of rainfall in an entire year. The flora and fauna that survive there have to be tough. Desert plants have evolved strategies to save water. In wet biomes, plants can have very large leaves—and they use them to catch as many rays as possible—but large leaves also lead to water loss. To conserve water, desert plants have very tiny leaves, or no leaves at all, transferring the work of photosynthesis to their trunks or stems. That’s why cacti have green “trunks.”

Desert animals also have to deal with high temperatures and minimal water supplies. Typically, they are nocturnal, hiding out in burrows during the day to beat the heat. Some animals, such as the desert tortoise, go into “estivation” in their burrows during the hottest part of the year. Estivation is the desert version of hibernation—the animal’s pulse and breathing slow down dramatically—so that they don’t need to use much water or energy.

The saguaro [suh-WAHR-oh] cactus grows in the deserts of the southwestern United States. When it rains, the trunk of the saguaro can expand to hold water. Sharp spines defend it from animals who might try to break open the saguaro and take a drink. (Nelson Sirlin/ Shutterstock)

The smallest fox in the world, the fennec fox lives in Africa’s Sahara desert. Its most obvious adaptation to desert life is its oversized ears. With blood vessels very close to the skin surface, the big ears help the fox radiate body heat and keep cool. What is unseen is the fox’s ability to conserve water—it rarely needs to take a drink. (Cat Downie/ Shutterstock)

Chameleons are famous for their ability to change color and blend in with their surroundings. The Namaqua chameleon of southwestern Africa is no exception. However, unlike other chameleons that live in trees, this desert-dwelling species digs burrows in the sand to make its home. The Namaqua chameleon uses its long, sticky tongue to nab insects and scorpions. (almondd/ Shutterstock)

Desert-adapted dromedaries (one-humped camels) were domesticated thousands of years ago. People ride them, drink their milk, and even race them. Camels can travel for 100 miles across the desert without water, and they can easily handle temperatures of 110 degrees Fahrenheit, This one is hanging out on a beach next to Dubai, waiting to take tourists for a ride. (Cherkas/ Shutterstock)

Mediterranean

This is one of the world’s smallest biomes, occurring on the west coast of the United States (particularly in California), along the coast of the Mediterranean Sea, and in coastal patches of South Africa, Australia, and Chile. Winters are mild in this biome, and what little rain there is, falls in that season. Summers are dry and hot. But it’s not a desert.

The plants of the Mediterranean biome are evergreen and shrubby, and they grow very densely.  Many have thick, leathery leaves that seal in moisture or leaves with small surface areas to limit water loss. The plants also have adapted to survive occasional wildfires. Some, such as chamise, can grow new shoots from underground roots, even though everything above ground has burned.

The Mediterranean biome is highly aromatic—with many plants emitting strong, spicy smells. Many herbs used for cooking—including rosemary, thyme, sage, and oregano—all grow wild in the coastal shrubbery surrounding the Mediterranean Sea.

Growing up to nine feet high in Southern California, this tower of flowers emerges from the low-growing plant below, which is known as Spanish bayonet (for its bladelike leaves). The gray-green color of Spanish bayonet is typical of many plants in the Mediterranean zone. The light-colored leaves reflect heat better than darker colors, and that helps plants conserve water in this dry environment. (Mariusz S. Jurgielewicz/ Shutterstock)

One of many sub-species of rattlesnake, the black diamond rattler hunts rodents in California’s chaparral at night. If disturbed or threatened, it will vibrate the rattle at the end of its tail as a warning. Its venom is extremely toxic. (Audrey Snider-Bell/ Shutterstock)

Tropical Rain Forest

Located in a belt around the equator, rain forests are a riot of life, with plants growing non-stop year-round. The hot, wet climate supports a jungle of plants and wildlife, from the towering trees that make up the canopy down to the dark forest floor where sunlight barely penetrates due to the thickness of the foliage above. Rain forests get drenched by as much as 180 inches of rain annually.

The rain forest has more species than any other biome. Trees in the rain forest grow as high as 200 feet, and each tree may be home to hundreds of species, from vines and bromeliads, to butterflies, monkeys, birds, and frogs.

Rain forests once covered about 14 percent of the Earth’s land surface, but now account for only about 6 percent. Rain forest habitats continue to be cut down for their wood products and to create land for farming. Every year about 9,000 square miles of rain forest is cut down—that’s an area about the size of New Jersey.

Howler monkeys live almost entirely in the rain forest canopy. Leaves are the main part of their diet, so they have everything they need high in the sky. Since it’s hard to see through the greenery in the canopy, animals that live there make a lot of noise to communicate. In fact, howler monkeys are thought to be the loudest animals on land. Their bloodcurdling roars can be heard for three miles. (Micha Klootwijk/ Shutterstock)

Plants grow everywhere in the rainforest—even on other plants. This tree trunk in Panama’s rain forest is home to several bromeliads. The mop-top leaves of each bromeliad form a bowl-shape that catches rainwater—and these tiny ponds in the sky are home to insects and even frogs. (Alfredo Maiquez/ Shutterstock)

Madagascar’s rain forests are filled with astonishing animals, from lemurs and aye-ayes to flying foxes and fossas. This Comet Moth, also called the Madacascan Moon Moth, is one of the largest moths in the world, with a wingspan of eight inches and a six-inch-long tail. It evolved its showy appearance to attract mates. The eyespots mimic the red eyes of lemurs—and are there to confuse predators. (Anton_Ivanov/ Shutterstock)

About 40 species of toucans live in rain forests in Central and South America. These big-billed birds nest in tree hollows and eat mostly forest fruits. The crimson-rumped toucanet—pictured here—lives in the mountain rain forests of Ecuador. (Steve Hermann)

Written by Margaret Mittelbach

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