Endangered Plants and Ecosystems - Endangered Forests

species tropical habitat percent

Forests perform a wide variety of social and ecological functions. They provide homes and sustenance for forest dwellers, protect and enrich soils, affect local and regional climate through the evaporation and storage of water, and help stabilize the global climate by processing carbon dioxide.

Forests are broadly classified by latitude as either tropical, temperate, or boreal. Tropical forests, or rainforests, are predominantly evergreen and occur close to the equator, in areas with plentiful rain and little temperature variation year-round. There are tropical forests in Central and South America, Africa, South and Southeast Asia, and Australia. Tropical forests are characterized by the greatest diversity of biological species. For example, as many as one hundred distinct tree species may inhabit a square kilometer. Vegetation is often so dense in tropical forests that very little light FIGURE 4.4
Present and historic distribution of Mead's milkweed by county
penetrates to the ground. Temperate forests are found in areas with distinct warm and cold seasons, including North America, northern Asia, and western and central Europe. Many temperate forests are made up of deciduous trees—species that shed their leaves during winter. Plant diversity is not as great in temperate forests as in rainforests. There are perhaps three or four tree species per square kilometer. Boreal forests, also known as taiga, are found at high latitudes in extremely cold climates where the growing season is short. Precipitation generally falls as snow rather than rain. Boreal forest flora includes evergreen trees and lichen ground cover. Boreal forests are present in Siberia, Scandinavia, Alaska, and Canada.


Deforestation refers to the destruction of forests through the removal of trees, most often by clear-cutting or burning. It results in habitat loss for countless species of plants as well as animals. Deforestation is occurring globally, but is proceeding at a particularly alarming rate in the world's tropical rainforests, which comprise the most diverse ecosystems in the world. Deforestation is one of the most pressing environmental issues today.

In addition to destruction of habitat for numerous plant and animal species, the loss of forests has other effects as well. For example, forests play a crucial role in the global cycling of carbon—vegetation stores two trillion tons of carbon worldwide, roughly triple the amount stored in the atmosphere. When forest trees are cleared, the carbon they contain FIGURE 4.5
Coast redwood trees in Redwood National Park, California. Redwoods are found only on the West Coast of North America and are the tallest trees on earth. (National Park Service)
is oxidized and released to the air, adding to the carbon dioxide in the atmosphere. The burning of the Amazon rainforests and other forests thus has a two-fold effect—the release of large amounts of carbon dioxide into the atmosphere and the loss of the trees that help absorb carbon dioxide.

Furthermore, deforestation also results in forest fragmentation, which is itself detrimental for several reasons. First, forest fragmentation creates more "edge" habitats and destroys habitat for deep-forest creatures. Second, fragmentation isolates plant and animal populations, making them more vulnerable to local extinction. Third, some non-native species thrive in edge habitats, and are able to invade and displace native species in a fragmented habitat. In North America, for example, songbirds like the wood thrush and the promontory warbler are declining due to increasing numbers of blue jays and parasitic brown-headed cowbirds, both of which flourish at forest edges. Finally, most trees are more susceptible to weather at forest edges.


Tropical forests are the world's most biologically rich habitats. These storehouses of biological diversity cover less

Mead's milkweed: Threats and recommended recovery actions

Listing factor Threat Recovery criteria Task
A Elimination of tallgrass prairie habitat due to urban development, agricultural expansion and detrimental agricultural practices 1, 2, 3 Identify and control threats to extant populations and available habitat, seek legal protection of sites, encourage landowners and agencies to manage habitat, survey for new populations or available habitat, and promote public understanding
C Infestation of beetle larvae (Curculionidae) and other pathogens 1, 2, 3 Conduct research on management of herbivores and pathogens that may reduce reproduction and maintain conservation populations
D The state of Kansas does not have specific legislation or rules to protect rare plants 1, 2 Protect habitat by landowner participation, seek legal dedication of habitat, acquirement of land by conservation organizations, maintain conservation populations, and promote public understanding
D The majority of known populations are on private property and are unprotected. 2 Protect habitat by landowner participation, seek legal dedication of habitat, acquirement of land by conservation organizations, and promote public understanding
E Lack of pollinators 1, 2, 3 Determine what species are pollinators
E Fluctuation of flowering plants and population numbers 3 Increase number of sites managed or owned by conservation organizations, manage habitat and conduct research on restoration, management and introduction techniques
Listing factors:
A = The present or threatened destruction, modification, curtailment of its habitat or range
B = Overutilization for commercial, recreational, scientific, educational purposes (not a factor)
C = Disease or predation
D = The inadequacy of existing regulatory mechanisms;
E = Other natural or manmade factors affecting its continued existence
Recovery criteria:
1. Twenty-one populations are distributed across plant communities and physiographic regions within the historic range of the species.
2. Each of these 21 populations is highly viable. A highly viable population is defined as follows: more than 50 mature plants; seed production is occurring and the population is increasing in size and maturity; the population is genetically diverse with more than 50 genotypes; the available habitat size is at least 125 acres (50 hectares); the habitat is in a late-successional stage; the site is protected through long-term conservation easements, legal dedication as nature preserves, or other means; and the site is managed by fire in order to maintain a late-successional graminoid-vegetation structure free of woody vegetation.
3. Monitoring data indicates that these populations have had a stable or increasing trend for 15 years.
SOURCE: "Appendix 7. Summary of Threats and Recommended Recovery Actions," in Mead's Milkweed (Asclepias meadii) Recovery Plan, U.S. Fish and Wildlife Service, Great Lakes-Big Rivers Region (Region 3), Fort Snelling, MN, September 2003

than 1 percent of the earth, but are home to 50 to 90 percent of the world's species. Many rainforest species have yet to be discovered and described by humans. In May 2002 for example, ornithologists announced the discovery of a new species of parrot, described as possessing green feathers, a hooked neck like a vulture, and a bald orange head. If new discoveries are being made even among well-studied groups such as birds, one can only imagine the untold number of insects or plants that remain to be studied.

Tropical forests are also the most critically endangered of habitats and are shrinking faster than ever—about 42 million acres a year are lost, or 80 acres each minute. The primary threats to rainforests are logging and clearing for farms and ranches. Satellite photographs show that as much as 10 percent of the Amazon rainforest has been destroyed, mainly through "slash and burn" clearing for agricultural use. Conservative estimates suggest rates of decline as high as 6.5 percent per year for rainforests in the Cote d'Ivoire in Africa, and an average of 0.6 percent per year for all tropical forests. At this pace, all rainforests will be cleared within 177 years. Given the growth in human population and economic activity in developing countries, the rate of deforestation is more likely to increase than to stabilize. Losses have been greatest so far in West Africa, Brazil, Central America, Mexico, Southeast Asia, and Madagascar.

The major underlying causes of tropical deforestation are underdevelopment, unemployment, and poverty among the growing populations of tropical countries. Unrestricted by enforceable regulations, farmers clear forests to create meager cropland that is often useless three years after its conversion—this is because tropical forest soils are poor, because almost all available nutrients are locked up in the trees and other biomatter. Logging and the conversion of forestland to unsustainable, short-term agricultural use have resulted in the destruction of habitats, declining fisheries, erosion, and flooding. Forest loss also disrupts regional weather patterns and contributes to global climate change. Finally, it eliminates plant and animal species that may serve important medical, industrial, and agricultural purposes. However, arguments for protective measures that might not pay off for many decades are often of little interest to farmers with families to feed. Developing countries frequently voice resentment over what they see as the hypocrisy of industrialized nations, which invariably engaged in similarly destructive practices to build their own economies.

Conservation of tropical forests presents a considerable challenge. The creation of "protected areas" alone has often proven ineffectual, mostly because the people who exploit forests are given no other options for meeting their economic needs. Many conservationists have started

Change in wetland area for selected wetland and deepwater categories, 1986–97
The coefficient of variation (CV) for each entry (expressed as a percentage) is given in parentheses.

Area in thousands of acres
Wetland/Deepwater Category Estimated area, 1986 Estimated area, 1997 Change, 1986–97 Change (in percent)
Marine Intertidal 133.1
Estuarine Intertidal Non-vegetated1 580.4
Estuarine Intertidal Vegetated2 4,623.1
All Intertidal Wetlands 5,336.6
Freshwater Non-vegetated3 5,251.0
Freshwater Vegetated4 95,548.1
Freshwater Emergent 26,383.3
Freshwater Forested 51,929.6
Freshwater Shrub 17,235.2
All Freshwater Wetlands 100,799.1
All Wetlands 106,135.7
Deepwater Habitats
Lacustrine5 14,608.9
Riverine 6,291.1
Estuarine Subtidal 17,637.6
All Deepwater Habitats 38,537.6
All Wetlands and Deepwater Habitats1,2 144,673.3
*Statistically unreliable
1Includes the categories: Estuarine Intertidal Aquatic Bed and Estuarine Intertidal Unconsolidated Shore.
2Includes the categories: Estuarine Intertidal Emergent and Estuarine Intertidal Shrub.
3Includes the categories: Paustrine Aquatic Bed, Palustrine Unconsolidated Bottom and Palustrine Unconsolidated Shore.
4Includes the categories: Palustrine Emergent, Palustrine Forested and Palustrine Shrub.
5Does not include the Great Lakes.
SOURCE: Thomas E. Dahl, "Table 2. Change in Wetland Area for Selected Wetland and Deepwater Categories, 1986 to 1997," in Status and Trends of Wetlands in the Conterminous United States 1986 to 1997, U.S. Fish and Wildlife Service, Washington, DC, 2000

to focus on the promotion of sustainable development within rainforests. Agroforestry describes an agricultural strategy that involves the maintenance of diversity within developed tropical forest areas. This includes planting many different types of crops in patches that are mixed in among grazing lands and intact forest. Agroforestry often focuses on crops that produce goods for an indefinite period of time, including citrus fruits, bananas, cacao, coffee, and rubber.

Agroforestry can help to maintain soil quality as well as tropical biodiversity, allowing for a sustained productivity that makes it unnecessary to clear more and more areas of forest. In addition, rainforest conservationists have promoted the harvest of sustainable rainforest products, rather than unsustainable products such as timber. Sustainable harvests include those of medicines, food, and rubber.

Finally, a recent trend is certification of tropical timber. It is estimated that as much as 70 percent of tropical timber available for sale in the United States represents "stolen timber" obtained through illegal logging. The Forest Stewardship Council, based in Oaxaca, Mexico, runs a program that certifies timber obtained from forests managed as sustainable environments. Large wood suppliers, such as Home Depot in 1999, opted to give preference to certified wood by 2002 following extensive picketing by protesters at several stores.

North American Forests

In 2003, the U.S. Forest Service reported that the United States has a total of 747 million acres of forestland. Of these, 20 percent belong to the National Forests, 13 percent are controlled by other federal agencies, 8 percent are owned by states, 49 percent are held by nonindustrial landowners, and 10 percent are held by industrial landowners.

Average annual net wetland loss for the conterminous United States, 1950s–1990s

Many U.S. forests are highly imperiled. One of the greatest threats to forests is deforestation via clear cutting, a method of logging in which all the trees in an area are cut. Serious damage to the old-growth forests of the Pacific Northwest, for example, is visible from National Aeronautics and Space Administration (NASA) satellite photos. Old-growth forests harbor many unique species, including numerous species that are threatened or endangered. An alternative to clear-cutting is selective management, in which only some trees are removed from an area. Even selective management practices, however, frequently deplete forests more quickly than they are able to recover. The lumber industry continues to battle with environmentalists and the U.S. Forest Service over the right to log National Forest lands, including the unique redwood forests of the West Coast. (See Figure 4.5.)

Huge forest fires raged through the western United States in 2000 and 2002. The Forest Service reported that these were two of the worst fire seasons in over fifty years. In 2002 forest fires scorched over 7 million acres and caused over $1.7 billion in damages. The fires were partly the result of long decades of fire suppression. In response, President Bush announced the "Healthy Forest Initiative" in 2002. This initiative was immediately attacked by conservationists, who claimed that its only aim was to roll back federal regulations on logging, and that it was intended to benefit logging companies rather than to protect people or wildlife. Conservationists further argued that the Bush Administration was merely using the forest fires as an excuse for forwarding its pro-business/anti-environment agenda.

Change in wetlands converted to various land uses, 1986–97

In addition to logging and fire risk, the Forest Service highlighted several other major threats to forests in its 2003 forest health update. These include:

  • Invasive insects and pathogens. Sudden Oak Death, caused by a new, unidentified pathogen, has killed thousands of oak and other species in coastal forests, mixed evergreen forests, and urban-wildland interfaces in California and southern Oregon. White Pine Blister Rust is a non-native fungus from Asia that has killed white pine trees in the western United States and Canada. The gypsy moth, first introduced from native habitats in Europe and Asia in the 1800s, continues to damage eastern U.S. forests. The hemlock woolly adelgid, native to Asia and introduced in the 1920s, continues to kill hemlock trees in the eastern United States.
  • Invasive plants. About 1,400 species of non-native plants are recognized as pest species that threaten forests and grasslands. Invasive plant species currently affect over 100 million acres of U.S. forestland. The Forest Service spends about $16 million annually in preventing the spread of invasive plants such as the "mile a minute" weed, which infests northeastern forests, and leafy spurge, which affects ecosystems in southern Canada and the northern United States.
  • Outbreaks of native insects. Certain native insects, including bark beetles, mountain pine beetles, and southern pine beetles, can also lay waste to native forests when they occur in large outbreaks.


During the first millennium A.D., an expanse of ancient forest flourished along the entire western coast of the United States and Canada. Today, a portion of this habitat, a 500-mile expanse along the southeastern coast of Alaska, has been preserved as FIGURE 4.8
Ecoregions of the United States
Tongass National Forest. Tongass National Forest represents an unblemished stretch of trees and other wildlife that has existed as a completely intact ecosystem for over a thousand years. It includes 17 million acres of pristine woodland and has never experienced an extinction in modern times. The Tongass preserve comprises 26 percent of the world's temperate rainforest and is the largest on earth.

In the mid-twentieth century, however, the federal government began to negotiate with logging companies to open small portions of the ancient forest for clear-cutting. This has generated ongoing debate in Congress. In the 1990s loggers appealed to the government to open more access roads to facilitate logging, whereas environmentalists fought to preserve the area from human tampering altogether. In May 2000 the National Forest Service drafted a proposal urging renewed protection of roadless areas. A lawsuit brought by the Natural Resources Defense Council in 2003 succeeded in protecting Tongass and other roadless national forests from logging. The Bush Administration exempted Tongass from these protections and is attempting to open 2.5 million acres of the forest to logging.

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