CHICAGO, Illinois, 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
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
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who created coffee plantations which have been replaced by an ever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
"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."