1. Biodiversity
Finz 2012

2. A World Rich in Biodiversity
Biodiversity, short for biological diversity, is the variety of organisms in a given area, the genetic variation within a population, the variety of species in a community, or the variety of communities in an ecosystem.
Certain areas of the planet, such as tropical rainforests, contain an extraordinary variety of species.
Humans need to understand and preserve biodiversity for our own survival.

3. Unknown Diversity
The study of biodiversity starts with the unfinished task of cataloging all the species that exist on Earth.
The number of species known to science is about 1.7 million, most of which are insects. However, the actual number of species on Earth is unknown.
Scientists accept an estimate of greater than 10 million for the total number of species.

4. Unknown Diversity

5. Unknown Diversity
New species are considered known when they are collected and described scientifically.
Unknown species exist in remote wilderness, deep oceans, and even in cities.
Some types of species are harder to study and receive less attention than large, familiar species.

6. Levels of Diversity
Biodiversity can be studied and described at three levels: species diversity, ecosystem diversity, and genetic diversity.
Species diversity refers to all the differences between populations of species, as well as between different species.
Ecosystem diversity refers to the variety of habitats, communities, and ecological processes within and between ecosystems.

7. Levels of Diversity
Genetic diversity refers to all the different genes contained within all members of a population.
A gene is a segment of DNA that is located in a chromosome and that codes for a specific hereditary trait.

8. Benefits of Biodiversity
Biodiversity can affect the stability of ecosystems and the sustainability of populations.
We depend on healthy ecosystems to ensure a healthy biosphere that has balanced cycles of energy and nutrients.
Species are part of these cycles.

9. Species Are Connected to Ecosystems
When scientists study any species closely, they find that it plays an important role in an ecosystem.
Every species is probably either dependent on or depended upon by at least one other species in ways that are not always obvious.
When one species disappears from an ecosystem, a strand in a food web is removed.

10. Species Are Connected to Ecosystems
Some species are clearly critical to the functioning of an ecosystem.
A keystone species is a species that is critical to the functioning of the ecosystem in which it lives because it affects the survival and abundance of many other species in its community.
An example is the sea otter. The loss of the sea otter populations led to an unchecked sea urchin population, which ate all the kelp leading to the loss of kelp beds along the U.S. Pacific Coast.

11. Species and Population Survival
The level of genetic diversity within populations is a critical factor in species survival.
Genetic variation increases the chances that some members of the population may survive environmental pressures or changes.
Small and isolated populations are less likely to survive such pressures.

12. Species and Population Survival
When a population shrinks, its genetic diversity decreases as though it is passing through a bottleneck.
Even if such a population is able to increase again, there will be inbreeding within a smaller variety of genes.
The members of the population may then become more likely to inherit genetic diseases.

13. Species and Population Survival

14. Medical and Industrial Uses
About one quarter of the drugs prescribed in the United Sates are derived from plants, and almost all of the antibiotics are derived from chemicals found in fungi.
New chemicals and industrial materials may be developed from chemicals discovered in all kinds of species.
The scientific community continues to find new uses for biological material and genetic diversity.

15. Medical Uses

16. Agricultural Uses
Most of the crops produced around the world originated from a few areas of high biodiversity.
Most new crop varieties are hybrids, or crops developed by combining genetic material from other populations.
History has shown that depending on too few plants for food is risky. Famines have resulted when an important crop was wiped out by disease. But some crops have been saved by crossbreeding them with wild plant relatives.

17. Agricultural Uses

18. Ethics, Aesthetics, and Recreation
Some people believe that we should preserve biodiversity for ethical reasons. They believe that species and ecosystems have a right to exist whether or not they have any other value.
People also value biodiversity for aesthetic or personal enjoyment such as keeping pets, camping, picking flowers, or watching wildlife.
Ecotourism is a form of tourism that supports the conservation and sustainable development of ecologically unique areas.

19. Biodiversity at Risk
The extinction of many species in a relatively short period of time is called a mass extinction
Earth has experienced several mass extinctions, each probably caused by a global change in climate.
It takes millions of years for biodiversity to rebound after a mass extinction.

20. Biodiversity at Risk

21. Current Extinctions
Scientists are warning that we are in the midst of another mass extinction.
The rate of extinctions is estimated to have increased by a multiple of 50 since 1800, with up to 25 percent of all species on Earth becoming extinct between 1800 and 2100.
The current mass extinction is different from those of the past because humans are the primary cause of the extinctions.

22. Species Prone to Extinction
Large populations that adapt easily to many habitats are not likely to become extinct.
However, small populations in limited areas can easily become extinct.
Species that are especially at risk of extinction are those that migrate, those that need large or special habitats, and those that are exploited by humans.

23. Species Prone to Extinction
An endangered species is a species that has been identified to be in danger of extinction throughout all or a significant part of its range, and that is thus under protection by regulations or conservation measures.
A threatened species is a species that has been identified to be likely to become endangered in the foreseeable future.

24. How Do Humans Cause Extinctions?
In the past 2 centuries, human population growth has accelerated and so has the rate of extinctions.
The numbers of worldwide species known to be threatened, endangered, or recently extinct are listed on the next slide.
The major causes of extinction today are the destruction of habitats, the introduction of nonnative species, pollution, and the overharvesting of species.

25. How Do Humans Cause Extinctions?

26. Habitat Destruction and Fragmentation
As human populations grow, we use more land to build homes and harvest resources.
In the process, we destroy and fragment the habitats of other species.
It is estimated that habitat loss causes almost 75 percent of the extinctions now occurring.

27. Habitat Destruction and Fragmentation
For example, cougars, including the Florida Panther, require expansive ranges of forest and large amount of prey.
Today, much of the cougars’ habitat has been destroyed or broken up by roads, canals, and fences.
In 2001, fewer than 80 Florida panthers made up the only remaining wild cougar population east of the Mississippi River.

28. Invasive Exotic Species
An exotic species is a species that is not native to a particular region.
Even familiar organisms such as cats and rats are considered to be exotic species when they are brought to regions where they never lived before.
Exotic species can threaten native species that have no natural defenses against them.

29. Harvesting, Hunting, and Poaching
Excessive hunting can also lead to extinction as seen in the 1800s and 1900s when 2 billion passenger pigeons were hunted to extinction.
Thousands of rare species worldwide are harvested and sold for use as pets, houseplants, wood, food, or herbal medicine.
Poaching is is the illegal harvesting of fish, game, or other species.

30. Pollution
Pesticides, cleaning agents, drugs, and other chemicals used by humans are making their way into food webs around the globe.
The long term effects of chemicals may not be clear until after many years.
The bald eagle was endangered because of a pesticide known as DDT. Although DDT is now illegal to use in the United States, it is still manufactured here and used around the world.

31. Areas of Critical Biodiversity
An important feature of areas of the world that contain greater diversity of species is that they have a large portion of endemic species.
An endemic species is a species that is native to a particular place and that is found only there.
Ecologists often use the numbers of endemic species of plants as an indicator of overall biodiversity because plants form the basis of ecosystems on land.

32. Tropical Rain Forests
Biologist estimate that over half of the world’s species live in these forests even though they cover only 7 percent of the Earth’s land surface.
Most of the species have never been described. Unknown numbers of these species are disappearing as tropical forests are cleared for farming or cattle grazing.
Tropical forests are also among the few places where some native people maintain traditional lifestyles.

33. Coral Reefs and Coastal Ecosystem
Reefs provide millions of people with food, tourism revenue, coastal protection, and sources of new chemicals, but are poorly studied and not as well protected by laws as terrestrial areas are.
Nearly 60 percent of Earth’s coral reefs are threatened by human activities, such as pollution, development along waterways, and overfishing.
Similar threats affect coastal ecosystems, such as swamps, marshes, shores, and kelp beds.

34. Islands
When an island rises from the sea, it is colonized by a limited number of species from the mainland. These colonizing species may then evolve into several new species.
Thus, islands often hold a very distinct but limited set of species.
Many island species, such as the Hawaiian honeycreeper, are endangered because of invasive exotic species.

35. Biodiversity Hotspots
The most threatened areas of high species diversity on Earth have been labeled biodiversity hotspots and include mostly tropical rainforests, coastal areas, and islands.
The hotspot label was developed by an ecologist in the late 1980s to identify areas that have high numbers of endemic species but that are also threatened by human activities.
Most of these hotspots have lost at least 70 percent of their original natural vegetation.

36. Biodiversity Hotspots

37. Biodiversity in the United States
The United States includes a wide variety of unique ecosystems, including the Florida Everglades, the California coastal region, Hawaii, the Midwestern prairies, and the forests of the Pacific Northwest.
The United States holds unusually high numbers of species of freshwater fishes, mussels, snails, and crayfish. Diversity is also high among groups of the land plants such as pine trees and sunflowers.

38. Biodiversity in the United States
The California Floristic Province, a biodiversity hotspot, is home to 3,488 native plant species.
Of these species, 2,124 are endemic and 565 are threatened or endangered.
The threats to this area include the use of land for agriculture and housing, dam construction, overuse of water, destructive recreation, and mining. All of which stem from local human population growth.

39. Saving Species One at a Time
When a species is clearly on the verge of extinction, concerned people sometimes make extraordinary efforts to save the last few individuals.
These people hope that a stable population may be restored someday.
Methods to preserve individual species often involve keeping and breeding the species in captivity.

40. Captive-Breeding Programs
Wildlife experts may attempt to restore the population of a species through captive-breeding programs.
These programs involve breeding species in captivity, with the hopes of reintroducing populations to their natural habitats.
This type of program has been used successfully with the Californian condor, for example. But the question remains whether or not these restored populations will ever reproduce in the wild.

41. Preserving Genetic Material
One way to save the essence of a species is by preserving its genetic material.
Germ plasm is hereditary material (chromosomes and genes) that is usually contained in the protoplasm of germ cells and may be stored as seeds, sperm, eggs, or pure DNA.
Germ-plasm banks store germ plasm in controlled environments for future use in research or species-recovery efforts.

42. Zoos, Aquariums, Parks, & Gardens
In some cases, zoos now house the few remaining members of a species and are perhaps the species’ last hope for survival.
Zoos, wildlife parks, aquariums, and botanical gardens, are living museums of the world’s biodiversity.
But, these kinds of facilities rarely have enough resources or knowledge to preserve more than a fraction of the world’s rare and threatened species.

43. More Study Needed
Ultimately, saving a few individuals does little to preserve a species as captive species may not reproduce or survive again in the wild.
Also, small populations are vulnerable to infectious diseases and genetic disorders caused by inbreeding.
Conservationists hope that these strategies are a last resort to save species.

44. Preserving Habitats and Ecosystems
The most effective way to save species is to protect their habitats.
Small plots of land for a single population is usually not enough because a species confined to a small area could be wiped out by a single natural disaster. While other species require a large range to find adequate food.
Therefore, protecting the habitats of endangered and threatened species often means preserving or managing large areas.

45. Conservation Strategies
Most conservationists now give priority to protecting entire ecosystems rather than individual species.
By doing this, we may be able to save most of the species in an ecosystem instead of only the ones that have been identified as endangered.
The general public has now begun to understand that Earth’s biosphere depends on all its connected ecosystems.

46. Conservation Strategies
While conservationists focus on the hotspots discussed earlier to protect biodiversity worldwide, they also support additional strategies.
One strategy is to identify areas of native habitat that can be preserved, restored, and linked into large networks.
Another promising strategy is to promote products that have been harvested with sustainable practices.

47. More Study Needed
Conservationists emphasize the urgent need for more serious study of the workings of species and ecosystems.
Only in recent decades has there been research into basic questions as, How much fragmentation can a particular ecosystem tolerate?
The answers to questions asked now may be years or decades away, but decisions affecting biodiversity continue to be made based on available information.

48. Legal Protection for Species
Many nations have laws and regulations designed to prevent the extinction of species, and those in the United States are among the strongest.
For example, in 1973, the U.S. Congress pass the Endangered Species Act.
The Endangered Species Act is designed to protect any plant or animal species in danger of extinction.

49. U.S. Laws
Under the first provision of the Endangered Species Act, the U.S. Fish and Wildlife Service (USFWS) must compile a list of all endangered and threatened species in the United States. As of 2002, 983 species of plants and animals were listed.
The second main provision of the act protects listed species from human harm.
The third provision prevents the federal government from carrying out any project that jeopardizes a listed species.

50. U.S. Laws

51. Recovery Plans
Under the fourth main provision of the Endangered Species Act, the USFWS must prepare a species recovery plan for each listed species. These plans often propose to protect or restore habitat for each species.
However, attempts to restrict human uses of land can be controversial. Real-estate developers may be prohibited from building in certain areas, and people may lose income and may object when their interests are placed below those of another species.

52. Habitat Conservation Plans
Battles between environmentalists and developers are widely publicized, and in most cases, compromises are eventually worked out. One form of compromise is a habitat conservation plan.
A habitat conservation plan is a land-use plan that attempts to protect threatened or endangered species across a given area by allowing some tradeoffs between harm to the species and additional conservation commitments among cooperating parties.

53. International Cooperation
At the global level, the International Union for the Conservation of Nature and Natural Resources (IUCN) facilitates efforts to protect species and habitats.
The IUCN publishes Red Lists of species in danger of extinction around the world, advises governments on ways to manage their natural resources, and works with groups like the World Wildlife Fund to sponsor projects such as attempting to stop poaching in Uganda.

54. International Trade and Poaching
One product of the IUCN has been an international treaty called CITES (the Convention on International Trade in Endangered Species).
The CITES treaty was the first effective effort to stop the slaughter of African elephants being killed by poachers who would then sell the ivory tusks.
In 1989, the members of CITES proposed a total worldwide ban on all sales, imports, and exports of ivory, hoping to put a stop the problem.

55. International Trade and Poaching
Some people worried that making ivory illegal might increase the rate of poaching instead of decrease it.
They argued that illegal ivory, like illegal drugs, might sell for a higher price.
But after the ban was enacted, the price of ivory dropped, and elephant poaching declined dramatically.

56. The Biodiversity Treaty
One of the most ambitious efforts to tackle environmental issues on a worldwide scale was the United Nations Conference on Environment and Development, also known as the first Earth Summit. An important result of the Earth Summit was the Biodiversity Treaty.
The Biodiversity Treaty is an international agreement aimed at strengthening national control and preservation of biological resources.

57. The Biodiversity Treaty
The treaty’s goal is to preserve biodiversity and ensure the sustainable and fair use of genetic resources in all countries.
However, the treaty took several years to be adopted into law by the U.S. government.
Some political groups objected to the treaty, especially to the suggestion that economic and trade agreements should take into account any impacts on biodiversity that might result from the agreements.

58. Private Conservation Efforts
Many private organizations work to protect species worldwide, often more effectively than government agencies.
For example, the World Wildlife Fund encourages the sustainable use of resources and supports wildlife protection. The Nature Conservancy has helped purchase millions of hectares of habitat preserves in 29 countries. Conservation International helps identify biodiversity hotspots. And, Greenpeace International organizes direct and sometimes confrontational actions.

59. Balancing Human Needs
Attempts to protect species often come into conflict with the interests of the world’s human inhabitants.
An endangered species might represent a source of food or income. Or a given species may not seem valuable to those who do not understand the species’ role in an ecosystem.
Many conservationists feel than an important part of protecting species is making the value of biodiversity understood by more people.

60. Graphic Organizer

61. Food and Agriculture
Finz 2012

62. Land Use and Land Cover
We use land for many purposes, including farming, mining, building cities and highways, and recreation.
Land cover is what you find on a patch of land, and it often depends on how the land is used. For example, land cover might be a forest, a field of grain, or a parking lot.
There are different types of land cover and different human uses for each cover type.

63. Land Use and Land Cover

64. Land Use and Land Cover
Urban describes an area that contains a city, or an area that contains 2,500 or more people and usually has a governing body, such as a city council.
Rural describes an area of open land that is often used for farming, or any population not classified as urban.
Most land provides one or more resources that humans consume. These resources include wood in forests, crops in farmland, and mineral resources.

65. Where We Live Until about 1850, most people lived in rural areas.
Many of them were farmers, who grew crops and raised livestock. Others managed the forests, worked in local mines or mills, or manufactured the necessities of life for the town.
The Industrial Revolution changed this pattern as machinery made it possible for fewer people to operate a farm or grain mill and better transportation allowed manufacturers to be located farther from their customers.

66. Where We Live
Thousands of rural jobs were eliminated, and many people had to move to cities to find jobs.
As a result, urban areas grew rapidly during the 20th century and spread over more land.
The movement of people from rural to urban areas happened in developed countries between about 1880 and Now, this movement is occurring rapidly in developing countries.

67. Where We Live
Today, most people throughout the world live in urban areas.

68. The Urban-Rural Connection
Whether people live in cities or in the countryside, people are dependent on resources produced in rural areas.
These resources include clean drinking water, fertile soil and land for crops, trees for wood and paper, and much of the oxygen we breath, which is produced by plants.
An ecosystem service is the role that organisms play in creating a healthful environment for humans.

69. The Urban-Rural Connection

70. Supporting Urban Areas
The area of rural land needed to support one person depends on many factors, such as the climate, the standard of living, and how efficiently resources are used.
Each person in a developed country uses the ecosystem services provided by about 8 hectares of land. But, many people in developing countries do not have access to all the resources for a healthy life, and may use ecosystem services from less than a hectare of land per person.

71. Urbanization
Urbanization is an increase in the ratio or density of people living in urban areas rather than in rural areas. People usually leave rural areas for more plentiful and better paying jobs in towns and cities.
In developed countries, urbanization slowed in the second half of the 20th century.
As urban populations have grown, many small towns have grown together and formed large urban areas called metropolitan areas. An example would be Washington D.C.-Baltimore.

72. Urbanization
Urban areas that have grown slowly are often relatively pleasant places to live, in part because roads and public transportation have been built to handle the growth allowing traffic to flow freely.
Buildings, roads, and parking lots are mixed with green spaces that provide these urban areas with much needed ecosystem services such as moderation of temperature, infiltration of rainwater runoff, and aesthetic value.

73. The Urban Crisis
A rapidly growing population, however, can overwhelm the infrastructure, leading to traffic jams, substandard housing, and polluted air and water.
Infrastructure is the basic facilities of a country or region, such as roads, bridges, sewers, and railroads.
When more people live in a city than its infrastructure can support, the living conditions deteriorate. This growth problem has become so widespread throughout the world that the term urban crisis was coined to describe it.

74. Urban Sprawl
Urban sprawl is the rapid spread of a city into adjoining suburbs and rural areas.
Much of this growth results in the building of suburbs, or housing and associated commercial buildings on the boundary of a larger town.
Many of these suburbs are built on land that was previously used for food production. In fact, each year suburbs spread over another 1 million hectares (2.5 million acres) of land in the United States.

75. Development on Marginal Lands
Many cities were first built where there was little room for expansion. As the cities grew, suburbs were often built on marginal land, or land that is poorly suited for building.
For example, Los Angeles was built in a basin, and has expanded onto slopes that are prone to landslides.
Structures built on marginal land can become difficult or impossible to repair and can be expensive to insure.

76. Other Impacts of Urbanization
Environmental conditions in the center of a city are different from those of the surrounding countryside, as cities both generate and trap more heat.
Heat island is an area in which the air temperature is generally higher than the temperature of surrounding rural areas.
Heat is generated by the infrastructure that makes a city run. Roads and buildings absorb and retain heat longer then vegetation does.

77. Other Impacts of Urbanization
Scientists are beginning to see that heat islands can affect local weather patterns. Hot air rises over a city, cooling as it rises, and eventually produces rain clouds.
In Atlanta, Georgia, and many other cities, increased rainfall is a side effect of the heat island effect.
The heat-island effect may be moderated by planting trees for shade and by installing rooftops that reflect rather than retain heat.

78. Urban Planning
Land-use planning is a set of policies and activities related to potential uses of land that is put in place before an area is developed.
The federal government requires developers to prepare detailed reports assessing the environmental impact of many projects, and the public has a right to comment on these reports.
Developers, city governments, local businesses, and citizens often disagree about land-use plans.

79. Intelligent Design
Land-use planners have sophisticated methods and tools available to them today.
The most important technological tools for land-use planning involve using the geographic information system.
A geographical information system (GIS) is an automated system for capturing, storing, retrieving, analyzing, manipulating, and displaying geographic data.

80. Intelligent Design
GIS software allows a user to enter different types of data about an area, such as the locations of sewer lines, roads, and parks, and then create maps with the data.
Each image corresponds to a different combination of information.
The power of GIS is that it allows a user to display layers of information about an area and to overlay these layers, like overhead transparencies, on top of one another.

81. Transportation
Most cities in the United States are difficult to travel in without a car.
Most cities in the United States were constructed after the invention of the automobile. In addition, availability of land was not a limiting issue, so many American cities sprawl over large areas.
By contrast, most cities in Europe were built before cars, and are compact with narrow roads.

82. Transportation
In many cities, mass transit systems were constructed in order to get people where they wanted to go. Mass transit systems use buses and trains to move many people at one time.
Mass transit systems save energy, limit the loss of land to roadways and parking lots, reduce highway congestion, and reduce air pollution.
Where the construction of mass transit systems is not reasonable, carpooling is an important alternative.

83. Open Space
Open space is land within urban areas that is set aside for scenic and recreational enjoyment. It also has many environmental benefits and provides valuable functions.
Open spaces include parks, public gardens, and bicycle and hiking trails.
Open spaces left in their natural conditions are often called greenbelts. These greenbelts provide important ecological services.

84. Open Space
The plants in open spaces absorb carbon dioxide, produce oxygen, filter out pollutants from air and water, and help keep a city cooler in the summer.
Open spaces, especially those with vegetation, also reduce drainage problems by absorbing more of the rainwater runoff from building roofs, asphalt, and concrete resulting in less flooding.
These open spaces also proved urban dwellers with much-needed places for exercise and relaxation.

85. GIS Views of Seattle, Washington

86. Land Management
The main categories of rural land are farmland, rangeland, forest land, national and state parks, and wilderness.
We have sometimes managed these lands sustainably so that they will provide resources indefinitely. We have also sometimes reduced their productivity by overusing or polluting them.
The condition of rural land is important because of the ecological services that it provides.

87. Farmlands
Farmland is land that is used to grow crops and fruit. The U.S. contains more than 100 million hectares of prime farmland.
However, in some places, urban development threatens some of the most productive farmland.
In 1996, the U.S. government established a national Farmland Protection Program to help state, county, and local governments protect farmland in danger of being paved over or otherwise developed.

88. Rangelands
Land that supports different vegetation types like grasslands, shrublands, and deserts and that is not used for farming or timber production is called rangeland.
Rangelands can be arid, like the rangelands in the desert Southwest, or relatively wet, like the rangelands of Florida.
The most common human use of rangeland is for the grazing of livestock.

89. Rangelands
Cattle, sheep, and goats are common livestock on the rangeland, which are valued for their meat, milk, wool, and hides.
Native wildlife also graze these lands.
Like farmland, rangeland is essential for maintaining the world’s food supply. World population growth may require a 40 percent increase in the food production of rangeland from 1977 to 2030.

90. Problems on the Range
Overgrazing is the depletion of vegetation due to the continuous feeding of too many animals.
Overgrazing often results in changes in the plant community. Less desirable plants may invade the area and replace more-desirable plant species.
In cases of severe overgrazing, all the vegetation that covers the land is eaten. Once the plants are gone, there is nothing to keep the soil from eroding.

91. Maintaining the Range
Much of the rangeland in the U.S. is public land managed by the federal government, which leases the rangeland to ranchers. However, much of the rangeland in the U.S. is degraded.
The Public Rangelands Improvement Act of 1978 was enacted to reverse this trend and improve land management practices.
Sustaining the productivity of rangeland generally means reducing overgrazing by limiting herds to sizes that do not degrade the land.

92. Maintaining the Range
Improving rangeland that has been degraded by overgrazing often includes methods such as killing invasive plants, planting native vegetation, and fencing areas to let them recover to the state they were in before they were overgrazed.
Ranchers also control grazing by digging many small water holes so that the vegetation around a single water hole is not overgrazed.
Rangeland can also be left unused for periods of time so that the vegetation can recover.

93. Forest Lands
Trees are harvested to provide products we use everyday, such as paper, furniture, and lumber and plywood for our homes.
In addition to wood and paper, we also value forest products such as maple syrup and turpentine.
There are many ecosystem services provided by forests. However, one of the most important is the removal of CO2 from the air.

94. Harvesting Trees People use enormous amounts of wood.
The worldwide average is 1,800 cm3 of wood used per person each day.
However, on average, each person in the United states uses about 3.5 times this amount.
About 1.5 billion people in developing countries depend on firewood as their main source of fuel.

95. Harvesting Trees
The timber industry classifies forest lands into three categories:
Virgin forests: forests that have never been cut.
Native forests: forests that are planted and managed.
Tree farms: areas where trees are planted in rows and harvested like other crops.
The two most widely used methods of harvesting trees are clear-cutting and selective cutting.

96. Harvesting Trees
Clear-cutting is the process of removing all of the trees from and area of land. Clear-cutting large areas destroys wildlife habitat and causes soil erosion.
Selective cutting is the process of cutting and removing only middle-aged or mature trees. It is more expensive than clear-cutting, but is usually much less destructive. It is usually practiced on smaller areas owned by individuals.

97. Harvesting Trees

98. Deforestation Deforestation is the process of clearing forests.
Most countries become severely deforested as populations expand and the demand for forest products increases.
Forests are cleared to convert the land into farmland, and to make space for roads, homes, factories, and office buildings.
Deforestation reduces wildlife habitat, but it has other impacts, too.

99. Deforestation
For example, when forests are cleared from hillsides, soil erosion usually results if the area is not quickly planted with a cover crop. Without tree roots to hold the soil in place, it is easily washed or blown away into the valley below.
The rate of deforestation is especially high in tropical rain forests, where the soil is relatively thin. Farmers who clear forests in these areas must always move from one plot of land to another, clearing more forest land each time.

100. Reforestation
Reforestation is the reestablishment and development of trees in a forest land.
In some places, reforestation is happening faster than trees are being cut down.
The price of deforestation, which causes soil erosion, landslides, and flooding, is sometimes too high, so in some areas the forest has been allowed to regenerate or has been replanted.

101. Reforestation
Some governments require reforestation after timber has been harvested from public land. However, worldwide, more than 90 percent of all timber comes from forests that are not managed by an agency that monitors the health of forest ecosystems.
Many governments are currently working to improve reforestation efforts and to promote less destructive methods. Private organizations have established tree-planting programs on roadsides and in cities.

102. Parks and Preserves
In the 1870s, a group of explorers approached Congress with news of a magnificent expanse of land in Wyoming and Montana they believed would be damaged by the development that had changed the northeastern United States.
Congress agreed to protect this land by setting it aside for the public to use and enjoy, and the first national park, Yellowstone, was created.
Today, the U.S. has about 50 national parks.

103. Parks and Preserves

104. Parks and Preserves
Most public lands are not as protected as the national parks are.
Some public lands are leased to private companies for logging, mining, and ranching. Others are maintained for hunting, fishing, wild-life refuges, or to protect endangered species.
International efforts include the Biosphere Program that has set up several hundred preserves, called biosphere reserves, that include people in the management plan of the reserves.

105. Parks and Preserves

106. Wilderness
The U.S. Wilderness Act, passed in 1964, designated certain lands as wilderness areas.
Wilderness is a region that is not cultivated and that is not inhabited by humans.
So far, 474 regions covering 32 million acres have been designated as wilderness in the United States. These areas are open to hiking, fishing, and camping. Building roads or structures and using motorized equipment is not allowed in wilderness areas.

107. Benefits of Protected Areas
Protected areas often provide the only place where unspoiled forests, deserts, or prairies remain. Without these areas, the plants and animals that can survive only in these ecosystems would disappear.
Wilderness areas serve as outdoor classrooms and research labs where people can learn more about the natural world.
These protected areas also provide recreation, such as hiking and camping, for many people.

108. Threats to Protects Areas
Around the world, more people visit national parks and wilderness areas each year and leave their mark on the land. Litter and traffic jams now plague many of our national parks.
Rangelands, mining and logging sites, oil and gas operations, power plants, and urban areas are often close enough to affect the parks.
In addition, preserved areas are affected by climate change and by air and water pollution, as are most other parts of the world.

109. Threats to Protect Areas
In attempts to protect wilderness from damage, limits have been set in some areas on the number of people permitted in the area at any given time.
Some areas are completely closed to visitors to allow wild animals to breed.
In addition, volunteer programs are now active in many wilderness areas. Volunteers help pick up trash, build trails, control invading or exotic species, and help educate the visiting public.

110. Quick LAB