Slash-and-burn agriculture in the rainforest of Borneo. Click image for more pictures. (Photo by R. Butler)
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LOSS OF SPECIES FOR FOREST REGENERATION
By Rhett Butler | Last updated July 22, 2012
A fully functioning forest has a great capacity to regenerate. But exhaustive hunting of tropical rainforest wildlife
can reduce those species necessary to forest continuance and regeneration. For example, in Central Africa, the
loss of species like gorillas, chimps, and elephants undercuts the 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, humans are encountering 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 epidemic 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 proliferation
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 less so 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 — which is estimated to infect 300 million people a year worldwide, killing 1-2 million — is a major threat to forest-dwelling indigenous peoples who have developed little or no (in the case of uncontacted tribes) resistance to the disease and lack access to antimalarial drugs. Malaria in the 1990s was cited for killing an estimated 20 percent of the Yanomani in Brazil and Venezuela. Drug-resistant forms of malaria means the disease is again becoming a threat in places where it was thought to be under control. Models suggest that climate change could expand the distribution of malaria-carrying mosquitos.
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,
a 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 among the city's large population 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. 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?
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