Biological Diversity under Attack

                                           vymazat čísla

To date, biologists have described fewer than 1 million of the earth's natural species.  There is
no certainty about how many species exist, although scientific estimates range from a conservative
3 million to 30 million. However, despite disagreement about the total number of species, there is
general consensus among scientists that at least half of the world's species live in the rain
forests of the earth's tropical regions. To appreciate the immense biodiversity in these forests,
consider the following figures: There are approximately thirty-two native species of trees in the
United Kingdom today. However, in each of two small plots of rain forest in

Peru (roughly one-millionth the area of the United Kingdom), a U.S. researcher identified
approximately three hundred tree species.^s

For some years, however, the moist forests of the earth's tropical regions have been the scene of
massive destruction as humans cut down or burn the trees to provide hardwood or land for
agriculture and settlement. By 1990, for example, the total deforestation in Brazil's Amazon region
amounted to 41.5 million hectares, the equivalent of an area as large as Sweden. Elsewhere in the
1980s, Malaysia destroyed an estimated 2.7 million hectares of its tropical forests at an annual
rate of 1.3 percent. During the same decade, Indonesia lost 10 million hectares of rain forests an
area larger than Portugal or the state of Indiana. Today the tropical rain forests of Southeast
Asia and South America continue to retreat at a rate in excess of ninety thousand square kilometers
a year.'

For tropical species, such massive deforestation means equally massive habitat destruction, which
in turn is causing the extinction of species on a scale unprecedented in human history. A 1989
study, which assumed a conservative total of 2 million species living exclusively in the tropical
rain forests, estimated that between four thousand and six thousand species a year are currently
being driven to extinction. Even these conservative estimates, the study points out, represent a
rate of extinction approximately ten thousand times greater than the extinction rate that existed
prior to the appearance of humans on the earth. Other studies suggest that the extinction rate
could rise to between seven thousand and twenty-seven thousand species a year.^l1

For a number of reasons, the threatened species of the rain forests are an immense and
irreplaceable resource. First, because of their genetic diversity, they are a source of genetic
material that can be utilized to support or replace domesticated varieties that become susceptible
to pests or disease. For example, the wild American oil palm has a natural resistance to spear rot,
a disease that is destroying the domesticated African oil palm. Researchers are using genes from
the American plant to develop resistance to the disease in its African cousin.

Second, tropical species are a potentially vast source of tree and plant species that could be
domesticated for human use. Twenty-four crop species have been domesticated in the Amazon region
alone, and countless numbers remain. Caryocar villosum is a tree that produces fruit valued highly
by Amazonian peoples. The Copaifera tree species produce substances that can substitute for diesel
fuel.

As a potential source of medicinal drugs, tropical species are irreplaceable. Wilson cites the
example of Catharanthus roseus, a small plant native to Madagascar. It produces two substances,
vinblastine and vincristine, which are extremely effective in the treatment of two forms of cancer.
The income from these two substances exceeds $100 million a year. None of the five other species of
Catharanthus has been carefully studied. One of the five is close to extinction because its habitat
is threatened by deforestation.

What can be done to preserve the biological diversity of the tropical rain forests, with its wealth
of scientific information and its unrealized potential as a source of material benefits? The
prospects are poor that the extinctions can be completely halted.^ls However, many experts are
cautiously optimistic that today's rate of extinction can be slowed if we address both the
immediate and the root causes of the crisis.

Establishing forest reserves-areas where all economic exploitation of the forest is forbidden –
will protect tropical species by preserving their habitats. Conservation measures such as these are
necessary in the fight against deforestation, the immediate cause of biodiversity loss; by
themselves, however, they are insufficient responses to the problem.

A second essential step is to address the root cause of the problem-the economic pressures that
cause people to destroy the forests for short-term gain. Accomplishing this, however, will be a
major challenge for the international community because it will involve tackling the complex and
related problems of poverty, overpopulation, and unsustainable development.

At the same time, we need to accelerate the pace of scientific research into the species of the
tropical rain forests. Such research is our only means of identifying areas that should be given
priority in conservation decisions. It will also provide necessary information about the value of
as yet unstudied species. This information will help reduce human ignorance about our dependence on
the natural world and will clearly be needed if we are eventually to convince people that the
biological resources of the rain forests are worth preserving.




Pakenham, J. Making Connections, CUP, 1998