Page 349 - Environment: The Science Behind the Stories

THE SCIENCE BEHIND THE STORY

Forest Fragmentation as island biogeography theory predicts.
in the Amazon To slow down species loss by 10 times,
researchers found that a fragment needs
to be 1000 times bigger. Even 100-ha
What happens to animals, plants, and
ecosystems when we fragment a for- fragments were not large enough for
est? A massive experiment smack in some animals, and lost half their species
the middle of the Amazon rainforest is in less than 15 years. Monkeys died out
helping scientists learn the answers. because they need large ranges. So did
Stretching across 1000 km Dr. Thomas Lovejoy, founder of the colonies of army ants and the birds that
2
(386 mi ), the Biological Dynamics of BDFFP follow them to eat insects scared up as
2
Forest Fragments Project (BDFFP) is the ants swarm across the forest floor.
the world’s largest and longest-running established within the large expanses Fragments distant from continu-
experiment on forest fragmentation. For of continuous forest still surrounding ous forest lost more species, but data
over 30 years, hundreds of researchers the pastures, to serve as control plots revealed that even very small openings
have muddied their boots in the rainfor- against which the fragments could be can stop organisms adapted to deep
est here, publishing over 700 scientific compared. interior forest from dispersing to recolo-
research papers, graduate theses, and Besides comparing treatments nize fragments. Many understory birds
books. (fragments) and controls (continu- would not traverse cleared areas of only
The story starts in the 1970s as ous forest), the project also surveyed 30–80 m (100–260 ft). Distances of just
conservation biologists debated how to populations in fragments before and 15–100 m (50–330 ft) were insurmount-
apply island biogeography theory to for- after they were isolated. These data on able for some bees, beetles, and tree-
ested landscapes being fragmented by trees, birds, mammals, amphibians, dwelling mammals.
development. Biologist Thomas Lovejoy and invertebrates showed declines in Soon, a complication ensued:
decided some good hard data were the diversity of most groups (FIGURE 2). Ranchers abandoned many of the
needed. He conceived a huge experi- As researchers studied the plots pastures because the soil was unpro-
mental project to test ideas about forest over the years, they found that small ductive, and these areas began filling
fragmentation and established it in the fragments lost more species, and lost in with secondary forest. As this young
heart of the biggest primary rainforest them faster, than large fragments—just forest grew, it made the fragments
on the planet—South America’s Ama-
zon rainforest.
Farmers, ranchers, loggers, and BDFFP
miners were streaming into the Amazon Manaus
then, and deforestation was rife. If sci-
entists could learn how large fragments Amazon
had to be to retain their species, it rainforest
would help them work with policymak- Brazil
ers to preserve forests in the face of
development pressures.
Lovejoy’s team of Brazilians and
Americans worked out a deal with
Brazil’s government: Ranchers could
clear some forest within the study area
if they left square plots of forest stand-
ing as fragments within those clearings.
By this process, 11 fragments of three
sizes (1 ha [2.5 acres], 10 ha [25 acres],
and 100 ha [250 acres]) were left
standing, isolated as “islands” of forest,
surrounded by “seas” of cattle pasture
(FIGURE 1). Each fragment was fenced
to keep cattle out. Then, 12 study FIGURE 1 Experimental forest fragments of 1, 10, and 100 ha were created in the
plots (of 1, 10, 100, and 1000 ha) were BDFFP.

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