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Forest clearing in Peru. (Photo by R. Butler)
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LOSS OF SPECIES FOR FOREST REGENERATION
A fully functioning forest has a great capacity to regenerate. Exhaustive hunting of tropical rainforest species
can reduce those species necessary to forest continuance and regeneration. For example, in Central Africa, the
loss of species like gorillas, chimps, and elephants reduces the ability of seed dispersal and slows the recovery
of damaged forest. Loss of habitat in the tropics also affects the regeneration of temperate species. North American
migratory birds, important seed dispersers of temperate species, declined 1-3 percent annually from 1978-1988.
INCREASE OF TROPICAL DISEASES
The emergence of tropical diseases and outbreaks of new diseases, including nasty hemorrhagic fevers like ebola
and lassa fever, are a subtle but serious impact of deforestation. With increased human presence in the rainforest,
and exploiters pushing into deeper areas, man is encountering "new" microorganisms with behaviors unlike
those previously known. As the primary hosts of these pathogens are eliminated or reduced through forest disturbance
and degradation, disease can break out among humans. Although not unleashed yet, someday one of these microscopic
killers could lead to a massive human die-off as deadly for our species as we have been for the species of the
rainforest. Until then, local populations will continue to be menaced by mosquito-borne diseases like dengue fever,
Rift Valley fever, and malaria, and water-borne diseases like cholera.
Many emergent and resurgent diseases are directly linked to land alterations which bring humans in closer contact
with such pathogens. For example, malaria and snailborne schistosomiasis have escalated because of the creation
of artificial pools of water like dams, rice paddies, drainage ditches, irrigation canals, and puddles created
by tractor treads. Malaria is a particular problem in deforested and degraded areas, though not in forested zones where there
are few stagnant ground pools for mosquito breeding. These pools are most abundant in cleared regions and areas
where tractors tear gashes in the earth. Malaria is already a major threat to indigenous peoples who have developed
no resistance to the disease nor any access to antimalarial drugs. Malaria alone is cited as being responsible for killing
an estimated 20 percent of the Yanomani in Brazil and Venezuela. Malaria—caused by unicelluar parasites transferred in the
saliva of mosquitoes when they bite—is an especially frightening disease for its drug-resistant forms. Thanks
to poor prescribing techniques on the part of doctors, there are now strains in Southeast Asia reputed
to be resistant to more than 20 anti-malarial drugs. There is serious concern that global climate change will affect
the distribution of malaria, which currently infects roughly 270 million people worldwide and kills 1-2 million
a year— 430,000-680,000 children in sub-Saharan Africa alone.
The outbreak of disease in the tropics does not affect only the people of those countries, since virtually any
disease can be incubated for enough time to allow penetration into the temperate developed countries. For example,
any Central African doctor infected with the ebola virus from a patient can board a plane and land in London within 10
hours. The virus could quickly spread, especially if airborne, among the city's population of 8 million. Additionally,
every person at the airport who is exposed can unknowingly carry the pathogen home to their native countries around
the world.
According to the Centers for Disease Control (CDC) in Atlanta, deaths from infectious disease are on the rise.
Infectious disease is the leading cause of death worldwide and the third leading cause of death in the United States.
Though AIDS death rates are declining in wealthier countries, this infectious disease is still killing millions around the globe.
Demographers predict several African countries may achieve zero population growth within a generation partly due
to the toll from AIDS. Of even greater concern, according to the CDC, in 1994 10 percent of people who died before
50 did so suddenly and mysteriously, probably from some unidentified infection. Strangely, the U.S. invests only $42
million a year in infectious-disease surveillance, yet spends $225 million maintaining marching bands for the military
(Crenson 1997). The times may be changing, though: in the fall of 1997, Congress allocated funds for the establishment
of a world monitoring system to detect emerging infectious-disease outbreaks. Infectious disease have had a major
role in human mortality throughout history. At least one-third of human deaths during World War I came from an
infectious disease: influenza. In 1919, between 20 million and 100 million died from the flu—more than the number of total casualties
from the war.
Review questions:
- How is deforestation linked to the emergence of disease?
[print version | spanish | french | portuguese
| chinese | japanese]
Continued: Loss of Renewable Resources, Wildlife Conflict
This article was written by Rhett A. Butler [bibliographic citation for this page] and was last updated on the most recent date listed in the column on the right side.
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