CONCEPT 9-3 195
See how serious the habitat fragmentation
problem is for elephants, tigers, and rhinos at CengageNOW.■ CASE STUDY
A Disturbing Message from the Birds
Approximately 70% of the world’s nearly 10,000
known bird species are declining in numbers, and
roughly one of every eight (12%) of these bird species
is threatened with extinction, mostly because of habi-
tat loss, degradation, and fragmentation. About three-
fourths of the threatened bird species live in forests,
many of which are being cleared at a rapid rate, espe-
cially in the tropical areas in Asia and Latin America
(Figure 9-12).
Some 40% of Indonesia’s moist, tropical forests,
particularly in Borneo and Sumatra, has been cleared
for lumber and palm plantations. The harvested palm
oil is used as biofuel, mostly in European nations. As
a result, 75% of the bird species in Sumatra’s lowland
forests are on the verge of extinction.
In Brazil, 115 bird species are threatened, mostly
because of the burning and clearing of Amazon forests
for farms and ranches. Other threats to Brazil’s bird
species are the loss of 93% of Brazil’s Atlantic coastal
rain forest and, most recently, the clearing of the coun-
try’s savannah-like cerrado area to establish soybean
plantations.
A 2007 joint study by the National Audubon Society
and the American Bird Conservancy found that 30% ofSCIENCE FOCUS
Studying the Effects of Forest Fragmentation
on Old-Growth TreesSuch painstaking research reveals that
within 100 meters (330 feet) of the edge of
a forest fragment, typically up to 36% of the
biomass of old-growth trees is lost within
10-17 years after fragmentation. Plots in a
fragment’s interior show little loss of their
tree biomass. Scientists can use such data to
estimate how large a fragment must be in
order to prevent the loss of rare trees within
its protected core habitat. For more details
on this research see The Habitable Planet,
Video 9, at http://www.learner.org/resources/
series209.html.Critical Thinking
What are two ways to reduce the fragmenta-
tion of tropical rain forests?ropical rain forests typically consist of
large numbers of different tree spe-
cies with only a few members of each species
in an area. Thus, most of the old-growth tree
species in an area are rare and vulnerable to
local or regional extinction when the forest is
disturbed.
Tropical biologist Bill Laurance and his
colleagues have been studying the nature of
topical rain forests and how they are affected
by human activities for over 25 years. One of
his research interests is the effect of increas-
ing fragmentation of tropical rain forests as
people establish more roads, crop plantations,
settlements, and cattle grazing areas.
The edges of forest fragments are often
invaded by sun-loving species such as vines,
which can gradually take over and cause theT
loss of a fragment’s rare old-growth trees.
Laurance is trying to determine how large the
undisturbed inner core of a fragment must
be to afford protection to its rare old-growth
tree species.
His research team studies this by look-designated plots near the edge of a forest
fragment and in the fragment’s interior. In
this example of muddy-boots ecology, they
identify the tree species present in each plot.
Then they measure the height and diameter
of each tree to calculate its biomass and thus
the total biomass of the trees in each plot.
Such measurements are repeated every two
years for two decades or more to determine
changes in the species composition of the
study plots.609Number of
bird species4002001Figure 9-12 Distribution of bird species in North America and Latin
America. Question: Why do you think more bird species are found
in Latin America than in North America? (Data from The Nature
Conservancy, Conservation International, World Wildlife Fund, and
Environment Canada).Copyright 2009 Cengage Learning, Inc. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part.