November 10, 2003 (ENS): Fragmenting long established
land parcels can leave a damaged environment, new research
conducted in Tanzania by two University of Illinois-Chicago
biologists has documented. Habitat fragmentation in
the Tanzania's East Usambara Mountains was shown to
have broken a mutual relationship between a tree species
and the birds that distribute its seed.
University of Illinois-Chicago professor of biological
sciences Henry Howe, and doctoral candidate Norbert
Cordeiro focused their study on the Leptonychia tree,
Leptonychia usambarensis, called the "zonozono"
locally in the Swahili language. The tree is endemic
to the Eastern Arc biodiversity hotspot of Kenya and
The bird-tree dependency that evolved in this ancient
forest, isolated from other rainforests for 10 million
years, was broken by human development over the past
100 years, jeopardizing the leptonychia tree's survival.
Major funding for the study came from the Wildlife
Conservation Society and the National Science Foundation.
The research report was published today in the "Proceedings
of the National Academy of Sciences."
The study began in 2000 and is ongoing, in collaboration
with a team of Tanzanian researchers. While many studies
on the effects of fragmentation have been done in the
Americas, Cordeiro and Howe's study is one of few that
have been done in Africa.
Cordeiro, who is also a research associate with the
Tanzania Wildlife Research Institute, chose this critically
threatened location to compare how the trees fared in
larger continuous tracts of virgin forest with those
still growing in smaller parcels fragmented by farming
and old former colonial plantations.
The forests were first fragmented by the early German
colonists who created coffee plantations which have
been replaced by an ever expanding tea industry. Lowland
forests have been replaced with plantations of exotic
tree species and sisal.
The leptonychia tree's survival depends on certain
bird species to eat and disperse seed. But in the broken
parcels with few trees left, the birds were rare or
absent. Seed fell to the ground but did not regenerate
as well as in continuous forest tracts.
"It's been shown that land fragmentation has had
impacts on animal species, but there's been little study
to see if relationships between plants and animals are
affected too," said Cordeiro.
"We've shown here that's precisely the case. And
if other animals that depend on certain trees for food
are affected by habitat fragmentation, you could end
up with a cascading effect of extinction of trees and
seed dispersers, such as mammals and birds," he
Howe warns that findings such as this sound an alarm
about the consequences of rapid habitat fragmentation.
"We showed that a very common tree can be adversely
affected," he said, "which is a reason why
we suggest severing these relationships can accelerate
extinction, even of common species."
In the wake of the Industrial Revolution, the spread
of intensive agriculture and the fragmentation and elimination
of forests could set off a series of extinctions in
a couple of centuries, in which many of the world's
plants and animals are lost, the scientists warned.
"Some believe that as habitat patches get smaller
and smaller, the extinction of species is random,"
Howe said. "But this study shows it is not at all
random. It can be highly dependent and much more rapid
than random extinction. In fact, forest fragmentation
may even accelerate extinction of common species."
All of these species potentially are of use to people,
the researchers pointed out in a plea for attention
to the losses triggered by fragmentation. They help
stabilize the natural environment, the climate, retain
water and soil.
"The focus in Africa has been on preservation
of larger, charismatic mammals like elephants and rhinos,"
said Cordeiro. "But small birds and trees are rarely
studied in Africa."
"We can guess that their loss will be felt,"
Howe warned. "Ultimately, human actions may be
causing the equivalent of a large meteorite impact."