Land Fragmentation Breaks African Bird-Tree Bond

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 Tanzania.

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.

Amaani Tea Factory in the East Usambara Mountains (Photo courtesy Paul Oliver's Safaris)

The forests were first fragmented by the early German colonists who created coffee plantations which have been replaced by an ever expanding tea industry.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 said.

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."