Habitats
From expansive agricultural land and lush rain forests to rugged mountains and turbulent seas, explore the myriad landscapes that collectively cloak Earth and shelter life on it
Sustainable Agriculture
Sustainable agriculture takes many forms, but at its core is a rejection of the industrial approach to food production developed during the 20th century.
This system, with its reliance on monoculture, mechanization, chemical pesticides and fertilizers, biotechnology, and government subsidies, has made food abundant and affordable. However, the ecological and social price has been steep: erosion; depleted and contaminated soil and water resources; loss of biodiversity; deforestation; labor abuses; and the decline of the family farm.
The concept of sustainable agriculture embraces a wide range of techniques, including organic, free-range, low-input, holistic, and biodynamic.
The common thread among these methods is an embrace of farming practices that mimic natural ecological processes. Farmers minimize tilling and water use; encourage healthy soil by planting fields with different crops year after year and integrating croplands with livestock grazing; and avoid pesticide use by nurturing the presence of organisms that control crop-destroying pests.
Beyond growing food, the philosophy of sustainability also espouses broader principles that support the just treatment of farm workers and food pricing that provides the farmer with a livable income.
Critics of sustainable agriculture claim, among other things, that its methods result in lower crop yields and higher land use. They add that a wholesale commitment to its practices will mean inevitable food shortages for a world population expected to exceed 8 billion by the year 2030. There's recent evidence, though, suggesting that over time, sustainably farmed lands can be as productive as conventional industrial farms.
This system, with its reliance on monoculture, mechanization, chemical pesticides and fertilizers, biotechnology, and government subsidies, has made food abundant and affordable. However, the ecological and social price has been steep: erosion; depleted and contaminated soil and water resources; loss of biodiversity; deforestation; labor abuses; and the decline of the family farm.
The concept of sustainable agriculture embraces a wide range of techniques, including organic, free-range, low-input, holistic, and biodynamic.
The common thread among these methods is an embrace of farming practices that mimic natural ecological processes. Farmers minimize tilling and water use; encourage healthy soil by planting fields with different crops year after year and integrating croplands with livestock grazing; and avoid pesticide use by nurturing the presence of organisms that control crop-destroying pests.
Beyond growing food, the philosophy of sustainability also espouses broader principles that support the just treatment of farm workers and food pricing that provides the farmer with a livable income.
Critics of sustainable agriculture claim, among other things, that its methods result in lower crop yields and higher land use. They add that a wholesale commitment to its practices will mean inevitable food shortages for a world population expected to exceed 8 billion by the year 2030. There's recent evidence, though, suggesting that over time, sustainably farmed lands can be as productive as conventional industrial farms.
Deserts
Far from being barren wastelands, deserts are biologically rich habitats with a vast array of animals and plants that have adapted to the harsh conditions there. Some deserts are among the planet's last remaining areas of total wilderness. Yet more than one billion people, one-sixth of the Earth's population, actually live in desert regions.
Deserts cover more than one fifth of the Earth's land, and they are found on every continent. A place that receives less than 10 inches (25 centimeters) of rain per year is considered a desert. Deserts are part of a wider classification of regions called "drylands." These areas exist under a moisture deficit, which means they can frequently lose more moisture through evaporation than they receive from annual precipitation.
And despite the common conceptions of deserts as dry and hot, there are cold deserts as well. The largest hot desert in the world, northern Africa's Sahara, reaches temperatures of up to 122 degrees Fahrenheit (50 degrees Celsius) during the day. But some deserts are always cold, like the Gobi desert in Asia and the desert on the continent of Antarctica. Others are mountainous. Only about 10 percent of deserts are covered by sand dunes. The driest deserts get less than half an inch (one centimeter) of precipitation each year, and that is from condensed fog not rain.
Desert animals have adapted ways to help them keep cool and use less water. Camels, for example, can go for days without food and water. Many desert animals are nocturnal, coming out only when the brutal sun has descended to hunt. Some animals, like the desert tortoise in the southwestern United States, spend much of their time underground. Most desert birds are nomadic, crisscrossing the skies in search of food. Because of their very special adaptations, desert animals are extremely vulnerable to introduced predators and changes to their habitat.
Desert plants may have to go without fresh water for years at a time. Some plants have adapted to the arid climate by growing long roots that tap water from deep underground. Other plants, such as cacti, have special means of storing and conserving water. Many desert plants can live to be hundreds of years old.
Some of the world's semi-arid regions are turning into desert at an alarming rate. This process, known as "desertification," is not caused by drought, but usually arises from the demands of human populations that settle on the semi-arid lands to grow crops and graze animals. The pounding of the soil by the hooves of livestock may degrade the soil and encourage erosion by wind and water.
Global warming also threatens to change the ecology of desert. Higher temperatures may produce an increasing number of wildfires that alter desert landscapes by eliminating slow-growing trees and shrubs and replacing them with fast-growing grasses
Deserts cover more than one fifth of the Earth's land, and they are found on every continent. A place that receives less than 10 inches (25 centimeters) of rain per year is considered a desert. Deserts are part of a wider classification of regions called "drylands." These areas exist under a moisture deficit, which means they can frequently lose more moisture through evaporation than they receive from annual precipitation.
And despite the common conceptions of deserts as dry and hot, there are cold deserts as well. The largest hot desert in the world, northern Africa's Sahara, reaches temperatures of up to 122 degrees Fahrenheit (50 degrees Celsius) during the day. But some deserts are always cold, like the Gobi desert in Asia and the desert on the continent of Antarctica. Others are mountainous. Only about 10 percent of deserts are covered by sand dunes. The driest deserts get less than half an inch (one centimeter) of precipitation each year, and that is from condensed fog not rain.
Desert animals have adapted ways to help them keep cool and use less water. Camels, for example, can go for days without food and water. Many desert animals are nocturnal, coming out only when the brutal sun has descended to hunt. Some animals, like the desert tortoise in the southwestern United States, spend much of their time underground. Most desert birds are nomadic, crisscrossing the skies in search of food. Because of their very special adaptations, desert animals are extremely vulnerable to introduced predators and changes to their habitat.
Desert plants may have to go without fresh water for years at a time. Some plants have adapted to the arid climate by growing long roots that tap water from deep underground. Other plants, such as cacti, have special means of storing and conserving water. Many desert plants can live to be hundreds of years old.
Some of the world's semi-arid regions are turning into desert at an alarming rate. This process, known as "desertification," is not caused by drought, but usually arises from the demands of human populations that settle on the semi-arid lands to grow crops and graze animals. The pounding of the soil by the hooves of livestock may degrade the soil and encourage erosion by wind and water.
Global warming also threatens to change the ecology of desert. Higher temperatures may produce an increasing number of wildfires that alter desert landscapes by eliminating slow-growing trees and shrubs and replacing them with fast-growing grasses
Restoring Rivers
Rivers and their tributaries are the veins of the planet, pumping freshwater to wetlands and lakes and out to sea. They flush nutrients through aquatic ecosystems, keeping thousands of species alive, and help sustain fisheries worth billions of dollars.
Rivers are also the lifeblood of human civilizations. They supply water to cities, farms, and factories. Rivers carve shipping routes around the globe, and provide us with food, recreation, and energy. Hydroelectric plants built from bank to bank harness the power of water and convert it to electricity.
But rivers are also often the endpoint for much of our industrial and urban pollution and runoff. When it rains, chemical fertilizer and animal waste peppering residential areas and agricultural lands is swept into local streams, rivers, and other bodies of water. The result: polluted drinking water sources and the decline of aquatic species, in addition to coastal dead zones caused by fertilizer and sewage overload.
Over the course of human history, waterways have been manipulated for irrigation, urban development, navigation, and energy. Dams and levees now alter their flow, interrupting natural fluctuations and the breeding and feeding patterns of fish and other river creatures. Technology and engineering have changed the course of nature, and now we are looking for ways to restore flow and function to the planet’s circulatory system.
The Colorado River provides an excellent example of what happens when demand for river water—for cities, industry, energy production, and agriculture—threatens to outpace supply.
River Facts
Rivers are also the lifeblood of human civilizations. They supply water to cities, farms, and factories. Rivers carve shipping routes around the globe, and provide us with food, recreation, and energy. Hydroelectric plants built from bank to bank harness the power of water and convert it to electricity.
But rivers are also often the endpoint for much of our industrial and urban pollution and runoff. When it rains, chemical fertilizer and animal waste peppering residential areas and agricultural lands is swept into local streams, rivers, and other bodies of water. The result: polluted drinking water sources and the decline of aquatic species, in addition to coastal dead zones caused by fertilizer and sewage overload.
Over the course of human history, waterways have been manipulated for irrigation, urban development, navigation, and energy. Dams and levees now alter their flow, interrupting natural fluctuations and the breeding and feeding patterns of fish and other river creatures. Technology and engineering have changed the course of nature, and now we are looking for ways to restore flow and function to the planet’s circulatory system.
The Colorado River provides an excellent example of what happens when demand for river water—for cities, industry, energy production, and agriculture—threatens to outpace supply.
River Facts
- An unsettling number of large rivers—including the Colorado, Rio Grande, Yellow, Indus, Ganges, Amu Darya, Murray, and Nile—are now so overtapped that they discharge little or no water to the sea for months at a time.
- China is proceeding with a massive $60 billion project to transfer water from the Yangtze River Basin in the south to the water-short north. If completed it would be the largest construction project on Earth and would transfer 1.5 trillion cubic feet (41.3 billion cubic meters) of water per year—a volume equal to half that of the Nile River.
- After enduring 19 flood episodes between 1961 and 1997, Napa, California, opted to restore the Napa River floodplain for $366 million, instead of the more conventional flood-control strategy of channelizing and building levees.
Grasslands
Grasslands go by many names. In the U.S. Midwest, they're known as prairies. In South America, they're called pampas. Central Eurasian grasslands are referred to as steppes, while in Africa they're named savannas. What they all have in common is grass as their naturally dominant vegetation. Grasslands are found where there is not enough regular rainfall to support the growth of a forest, but not so little as to form a desert.
In fact, most grasslands are located between forests and deserts. About one quarter of the Earth's land is covered with grasslands, but many of these lands have been turned into farms. Grasslands are generally open and fairly flat, and they exist on every continent except Antarctica. Most lie in the drier portions of a continent's interior.
There are two different kinds of grasslands: tropical and temperate. Grasslands in the southern hemisphere tend to get more precipitation than those in the northern hemisphere. Some grasses grow more than 7 feet (2 meters), and have roots extending several feet into the soil.
Tropical grasslands are warm year round, but usually have a dry and a rainy season. One such tropical grassland, the African savanna, is home to some of the world’s most recognizable species, including elephants, giraffes, rhinos, zebras, lions, hyenas, and warthogs.
Temperate grasslands, which average between 10 and 30 inches (25 and 75 centimeters) of rain per year, have shorter grasses, sometimes just a few millimeters. These areas have two seasons: a growing season and a dormant season. During the dormant season, no grass can grow because it is too cold.
The animals that live in temperate grasslands have adapted to the dry, windy conditions. There are grazing animals like gazelle and deer; burrowing animals such as mice and jack rabbits; and predators such as snakes and coyotes. The North American grasslands were once home to millions of bison, before most of them were slaughtered by humans.
When rainy season arrives, many grasslands become coated with flowers, some of which can survive well into winter with the help of underground storage organs and thick stem bases.
No other habitat is as agriculturally useful to humans as grasslands. Soils tend to be deep and fertile, perfect for cropland or pastures. Much of the North American prairielands have been converted into one of the richest agricultural regions on Earth.
Fires, both natural and human-caused, are important in maintaining grasslands. Ancient hunting peoples set regular fires to maintain and extend grasslands, and prevent fire-intolerant trees and shrubs from taking over. Grasses are able to survive fires because they grow from the bottom instead of the top.
In fact, most grasslands are located between forests and deserts. About one quarter of the Earth's land is covered with grasslands, but many of these lands have been turned into farms. Grasslands are generally open and fairly flat, and they exist on every continent except Antarctica. Most lie in the drier portions of a continent's interior.
There are two different kinds of grasslands: tropical and temperate. Grasslands in the southern hemisphere tend to get more precipitation than those in the northern hemisphere. Some grasses grow more than 7 feet (2 meters), and have roots extending several feet into the soil.
Tropical grasslands are warm year round, but usually have a dry and a rainy season. One such tropical grassland, the African savanna, is home to some of the world’s most recognizable species, including elephants, giraffes, rhinos, zebras, lions, hyenas, and warthogs.
Temperate grasslands, which average between 10 and 30 inches (25 and 75 centimeters) of rain per year, have shorter grasses, sometimes just a few millimeters. These areas have two seasons: a growing season and a dormant season. During the dormant season, no grass can grow because it is too cold.
The animals that live in temperate grasslands have adapted to the dry, windy conditions. There are grazing animals like gazelle and deer; burrowing animals such as mice and jack rabbits; and predators such as snakes and coyotes. The North American grasslands were once home to millions of bison, before most of them were slaughtered by humans.
When rainy season arrives, many grasslands become coated with flowers, some of which can survive well into winter with the help of underground storage organs and thick stem bases.
No other habitat is as agriculturally useful to humans as grasslands. Soils tend to be deep and fertile, perfect for cropland or pastures. Much of the North American prairielands have been converted into one of the richest agricultural regions on Earth.
Fires, both natural and human-caused, are important in maintaining grasslands. Ancient hunting peoples set regular fires to maintain and extend grasslands, and prevent fire-intolerant trees and shrubs from taking over. Grasses are able to survive fires because they grow from the bottom instead of the top.
Rain Forest
Incubators of Life
In Brazil, which houses 30 percent of the remaining tropical rain forest on Earth, more than 50,000 square miles of rain forest were lost to deforestation between 2000 and 2005. Biologists worry about the long-term consequences. Drought may be one. Some rain forests, including the Amazon, began experiencing drought in the 1990s, possibly due to deforestation and global warming.
Efforts to discourage deforestation, mainly through sustainable-logging initiatives, are underway on a very limited basis but have had a negligible impact so far.
The rain forest is nearly self-watering. Plants release water into the atmosphere through a process called transpiration. In the tropics, each canopy tree can release about 200 gallons (760 liters) of water each year. The moisture helps create the thick cloud cover that hangs over most rain forests. Even when not raining, these clouds keep the rain forest humid and warm.
Plants in the rain forest grow very close together and contend with the constant threat of insect predators. They have adapted by making chemicals that researchers have found useful as medicines. Bioprospecting, or going into the rain forest in search of plants that can be used in foods, cosmetics, and medicines, has become big business during the past decade, and the amount that native communities are compensated for this varies from almost nothing to a share in later profits.
The National Cancer Institute (NCI) estimates that 70 percent of the anti-cancer plants identified so far are rain forest plants. A new drug under development by a private pharmaceutical company, possibly for treating HIV, is Calanolide A, which is derived from a tree discovered on Borneo, according to NCI.
Many trees and plants, like orchids, have been removed from the rain forest and cultivated. Brazil nut trees are one valuable tree that refuses to grow anywhere but in undisturbed sections of the Amazon rain forest. There, it is pollinated by bees that also visit orchids, and its seeds are spread by the agouti, a small tree mammal.
Efforts to discourage deforestation, mainly through sustainable-logging initiatives, are underway on a very limited basis but have had a negligible impact so far.
The rain forest is nearly self-watering. Plants release water into the atmosphere through a process called transpiration. In the tropics, each canopy tree can release about 200 gallons (760 liters) of water each year. The moisture helps create the thick cloud cover that hangs over most rain forests. Even when not raining, these clouds keep the rain forest humid and warm.
Plants in the rain forest grow very close together and contend with the constant threat of insect predators. They have adapted by making chemicals that researchers have found useful as medicines. Bioprospecting, or going into the rain forest in search of plants that can be used in foods, cosmetics, and medicines, has become big business during the past decade, and the amount that native communities are compensated for this varies from almost nothing to a share in later profits.
The National Cancer Institute (NCI) estimates that 70 percent of the anti-cancer plants identified so far are rain forest plants. A new drug under development by a private pharmaceutical company, possibly for treating HIV, is Calanolide A, which is derived from a tree discovered on Borneo, according to NCI.
Many trees and plants, like orchids, have been removed from the rain forest and cultivated. Brazil nut trees are one valuable tree that refuses to grow anywhere but in undisturbed sections of the Amazon rain forest. There, it is pollinated by bees that also visit orchids, and its seeds are spread by the agouti, a small tree mammal.
Tundra
Tundras are among Earth's coldest, harshest biomes. Tundra ecosystems are treeless regions found in the Arctic and on the tops of mountains, where the climate is cold and windy and rainfall is scant. Tundra lands are snow-covered for much of the year, until summer brings a burst of wildflowers.
Mountain goats, sheep, marmots, and birds live in mountain, or alpine, tundra and feed on the low-lying plants and insects. Hardy flora like cushion plants survive on these mountain plains by growing in rock depressions where it is warmer and they are sheltered from the wind.
The Arctic tundra, where the average temperature is 10 to 20 degrees Fahrenheit (-12 to -6 degrees Celsius), supports a variety of animal species, including Arctic foxes, polar bears, gray wolves, caribou, snow geese and musk-oxen. The summer growing season is just 50 to 60 days, when the sun shines 24 hours a day.
The few plants and animals that live in the harsh conditions of the tundra are essentially clinging to life. They are highly vulnerable to environmental stresses like reduced snow cover and warmer temperatures brought on by global warming.
The Arctic tundra is changing dramatically due to global warming. Already, more southern animals like the red fox have moved onto the tundra. The red fox is now competing with the Arctic fox for food and territory, and the long-term impact on the sensitive Arctic fox is unknown.
It is the Arctic's permafrost that is the foundation for much of the region's unique ecosystem, and it is the permafrost that is deteriorating with the warmer global climate. Permafrost is a layer of frozen soil and dead plants that extends some 1,476 feet (450 meters) under the surface. In much of the Arctic it is frozen year round. In the southern regions of the Arctic, the surface layer above the permafrost melts during the summer and this forms bogs and shallow lakes that invite an explosion of animal life. Insects swarm around the bogs, and millions of migrating birds come to feed on them.
With global warming, the fall freeze comes later and more of the permafrost is melting in the southern Arctic. Shrubs and spruce that previously couldn't take root on the permafrost now dot the landscape, potentially altering the habitat of the native animals.
Another major concern is that the melting of the permafrost is contributing to global warming. Estimates suggest that about 14 percent of the Earth’s carbon is tied up in the permafrost. Until recently, the tundra acted as a carbon sink and captured huge amounts of carbon dioxide from the atmosphere as part of photosynthesis. This process helped keep the amount of this greenhouse gas from accumulating in the atmosphere.
Today, however, as the permafrost melts and dead plant material decomposes and releases CO2, the tundra has flipped from a carbon sink to a carbon
Mountain goats, sheep, marmots, and birds live in mountain, or alpine, tundra and feed on the low-lying plants and insects. Hardy flora like cushion plants survive on these mountain plains by growing in rock depressions where it is warmer and they are sheltered from the wind.
The Arctic tundra, where the average temperature is 10 to 20 degrees Fahrenheit (-12 to -6 degrees Celsius), supports a variety of animal species, including Arctic foxes, polar bears, gray wolves, caribou, snow geese and musk-oxen. The summer growing season is just 50 to 60 days, when the sun shines 24 hours a day.
The few plants and animals that live in the harsh conditions of the tundra are essentially clinging to life. They are highly vulnerable to environmental stresses like reduced snow cover and warmer temperatures brought on by global warming.
The Arctic tundra is changing dramatically due to global warming. Already, more southern animals like the red fox have moved onto the tundra. The red fox is now competing with the Arctic fox for food and territory, and the long-term impact on the sensitive Arctic fox is unknown.
It is the Arctic's permafrost that is the foundation for much of the region's unique ecosystem, and it is the permafrost that is deteriorating with the warmer global climate. Permafrost is a layer of frozen soil and dead plants that extends some 1,476 feet (450 meters) under the surface. In much of the Arctic it is frozen year round. In the southern regions of the Arctic, the surface layer above the permafrost melts during the summer and this forms bogs and shallow lakes that invite an explosion of animal life. Insects swarm around the bogs, and millions of migrating birds come to feed on them.
With global warming, the fall freeze comes later and more of the permafrost is melting in the southern Arctic. Shrubs and spruce that previously couldn't take root on the permafrost now dot the landscape, potentially altering the habitat of the native animals.
Another major concern is that the melting of the permafrost is contributing to global warming. Estimates suggest that about 14 percent of the Earth’s carbon is tied up in the permafrost. Until recently, the tundra acted as a carbon sink and captured huge amounts of carbon dioxide from the atmosphere as part of photosynthesis. This process helped keep the amount of this greenhouse gas from accumulating in the atmosphere.
Today, however, as the permafrost melts and dead plant material decomposes and releases CO2, the tundra has flipped from a carbon sink to a carbon
Urban
Cities have existed for thousands of years and can be traced back to the river valley civilizations of Mesopotamia (present-day Iraq), Egypt, India, and China. At first, these settlements depended largely on agriculture and domestic cattle, but as they grew in size they became centers for merchants and traders.
Urban growth, also known as urbanization, accelerated dramatically with the advent of industrialization some 200 years ago. At that time, large numbers of people moved to cities in search of jobs, mostly in factories. But the most rapid growth has taken place over the past 50 years. While less than one-third of the world's population lived in cities in 1950, about two thirds of humanity is expected to live in urban areas by 2030. Most of that urbanization is taking place in Asia, Africa, and Latin America.
Urban is defined as "that which is characteristic of a city." But what exactly is a city? In the past, walls may have defined a city. But today's city boundaries are often blurred. Are suburbs, which are often called metropolitan areas, part of cities? Depending on the boundaries used, Tokyo can have a population of anywhere between 8 and 40 million people.
Cities make a lot of sense for humans. People are concentrated in a small space rather than being spread out over a large territory. This allows the government and others to provide more service such as water, electricity, and transportation to a larger number of people. Schools and shops are more easily accessible than in rural areas.
Cities have always been at the center of economic growth and technological advances. The promise of jobs and prosperity pulls people to cities. But their rapid growth has also brought with it many negative things: violence, poverty, overcrowding, health problems, and pollution. Many cities in developing countries in particular are growing too rapidly for their own good, with many residents unable to find jobs and forced to live in slums.
Urban expansion is also encroaching on wildlife habitats everywhere. Increasingly people live and work in close proximity to wild animals whose native habitats have been lost or broken up. Many animals—from mice and cockroaches to pigeons and squirrels—have adapted to city life, taking advantage of abundant food and warmer temperatures.
Urban growth, also known as urbanization, accelerated dramatically with the advent of industrialization some 200 years ago. At that time, large numbers of people moved to cities in search of jobs, mostly in factories. But the most rapid growth has taken place over the past 50 years. While less than one-third of the world's population lived in cities in 1950, about two thirds of humanity is expected to live in urban areas by 2030. Most of that urbanization is taking place in Asia, Africa, and Latin America.
Urban is defined as "that which is characteristic of a city." But what exactly is a city? In the past, walls may have defined a city. But today's city boundaries are often blurred. Are suburbs, which are often called metropolitan areas, part of cities? Depending on the boundaries used, Tokyo can have a population of anywhere between 8 and 40 million people.
Cities make a lot of sense for humans. People are concentrated in a small space rather than being spread out over a large territory. This allows the government and others to provide more service such as water, electricity, and transportation to a larger number of people. Schools and shops are more easily accessible than in rural areas.
Cities have always been at the center of economic growth and technological advances. The promise of jobs and prosperity pulls people to cities. But their rapid growth has also brought with it many negative things: violence, poverty, overcrowding, health problems, and pollution. Many cities in developing countries in particular are growing too rapidly for their own good, with many residents unable to find jobs and forced to live in slums.
Urban expansion is also encroaching on wildlife habitats everywhere. Increasingly people live and work in close proximity to wild animals whose native habitats have been lost or broken up. Many animals—from mice and cockroaches to pigeons and squirrels—have adapted to city life, taking advantage of abundant food and warmer temperatures.