For years, ecologists have theorized that establishing landscape corridors to connect otherwise isolated plant and animal habitats would encourage biological diversity. Now researchers working in South Carolina have demonstrated it, at least with plants.

The researchers, who report their findings in the current issue of the journal Science, surveyed dozens of test plots in forested areas of the Savannah River Site, a 310-square-mile swath of southeastern South Carolina originally set aside to produce nuclear weapons for the military. The plots are now managed by the federal Forest Service for pine production.

The researchers surveyed their sites regularly starting in 2000 and found that, over time, there was more plant diversity in patches connected by corridors than in other patches, even if they had the same total area or the same amount of “edge” space between cleared and wooded areas.

Patches connected by landscape corridors “had 20 percent more species of plants than unconnected patches,” said Ellen Damschen, the lead author of the report and a postdoctoral fellow at the University of California, Santa Barbara.

The finding is important, ecologists say, because the fragmentation of wild land by human activities is one of the most important threats to biodiversity. More and more, landscape managers are incorporating corridors into their plans, but there is relatively little data on effectiveness.

“People have done corridor experiments with fruit flies in bottles, but that is hardly the sort of thing that is going to be very compelling to a wildlife manager,” said Stuart L. Pimm, a professor of conservation ecology at Duke University, who is familiar with the new study.

“Were the results surprising? No,” he said. “But it s the kind of example that s going to go into a textbook because this shows that corridors work instead of us just thinking that they work.” Wildlife corridors have been established in areas like the Rocky Mountains, but researchers there are still studying whether the ones linking protected areas from the Yukon to Yellowstone actually improve wildlife diversity.

“It is surprising that we would see such a dramatic change over a short time scale,” Dr. Damschen said. But the research, also carried out by scientists from several other universities, shows that “plants can change relatively quickly through their interactions with the landscape and the animals that interact with them,” like birds and rodents that disperse seeds or insects that act as pollinators.

In part because the corridor-connected patches have more varieties of birds, insects and animals like mice, she said, “the number of seeds that reach a patch that s connected by a corridor is higher.”

Some ecologists had feared that the landscape corridors might also help spread invasive species, but that did not seem to happen on the test plots, the researchers wrote. They said that areas connected by corridors “retain more native species than do isolated patches, that this difference increases over time, and that corridors do not promote invasion by exotic species.”

That may be, Dr. Damschen suggested in an interview, because invasive species “are really good at moving and don t need corridors.”
(Por Cornelia Dean,The N.Y.Times, 06/09/2006)