Lemurs Called Key to Madagascar Forest Survival
8/2/99
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Title: Lemurs Called Key to Madagascar Forest Survival
Source: Environmental News Network
Status: Copyright 1999, contact source for permission to reprint
Date: August 2, 1999
In most tropical rainforests up to 90 percent of all tree species
rely on animals for the dispersal of their seeds.
The dry forests of western Madagascar are unusual because they have
the greatest diversity of trees in the world yet they are home to the
lowest diversity of animals that disperse tree seeds. Ganzhorn's
research shows that these forests fail to regenerate completely on
their own without help from the brown lemur.
"This is a unique result. In other forests, the guild of seed
dispersers is redundant. If one group drops out - or is shot out -
there are others that can fill in," said Ganzhorn.
Lemurs are among Madagascar's most endangered species. Madagascar's
once-rich array of wildlife has been decimated by habitat destruction
and by its growing human population's need for usable land and
forest products. Much of the land is under constant pressure from
illegal logging, burning and over-farming. The problem is critical
for lemurs, because they are native.
Since people arrived in Madagascar some 2,000 years ago, an estimated
97 percent of the island's dry deciduous western forests have been
destroyed and those that remain are extremely fragmented. Restoring
these forests is one of the highest conservation priorities
worldwide, according to a 1995 United Nation's Development Program.
Ganzhorn and his colleagues studied regeneration in both contiguous
and fragmented primary forest. The fragments ranged from about seven
to 1,500 acres. The researchers found 177 tree species at study sites
and determined that 20 trees or about 10 percent of the trees were
dispersed largely or entirely by lemurs.
Fecal analysis showed that these 20 tree species are dispersed
primarily by the brown lemur. Of the eight lemur species living in
these forests, the brown lemur is the only one that ingests and
excretes intact seeds larger than half an inch. Seven of the 20 tree
species have seeds this size or bigger.
Ganzhorn and his colleagues compared regeneration in forest fragments
with and without brown lemurs and found that without lemurs there was
significantly less regeneration of the 20 lemur-dispersed trees. In
contrast, there was no difference in regeneration for the 157 tree
species that do not depend solely on lemurs for dispersal.
"Our study presents evidence that the demise of a specific group of
dispersers has resulted in changed and impoverished tree regeneration
of a whole forest eco-system," the researchers wrote.
"It is insufficient to leave a forest alone to regenerate if lemurs
have been eliminated from it," said Ganzhorn. "We should reintroduce
lemurs, increase connectivity and especially stop fragmentation of
whatever is left."