First Evidence That Wildlife Corridors Boost Biodiversity, Study Says

John Roach
for National Geographic News
September 1, 2006
Conservation corridors are a boon for plant diversity, according to a
new study that researchers say proves a widely practiced but still
controversial theory.

The corridors are narrow strips of land that connect isolated patches of wild habitat, such as nature reserves, often trapped in seas of human developments such as farms and subdivisions.

Many experts say corridors benefit biodiversity by allowing plants and wildlife access to a wider range of resources.

For example, when food and water are scarce in one patch of habitat, they may be abundant in another. Without a corridor connecting the patches, some species would be unable to reach necessary resources.

But other scientists have said that corridors put species that use them at greater risk from dangers—such as vehicle traffic and pollutants—that lurk on either side of a narrow passage.

(Related news: "Animal Overpasses, Tunnels Offering Roadkill Remedy" [May 2004].)

Proof that the networks help preserve multiple plants and animals at large scales has remained elusive—until now.

A team of scientists led by Ellen Damschen, an ecologist at the University of California, Santa Barbara, carved up a vast swath of a South Carolina pine forest into six 5,382-square-foot (500-square-meter) experimental plots.

Over five years open patches of habitat that were connected to other patches via narrow corridors grew about 20 percent more plant species in each plot than isolated patches did.

"Corridors have a positive impact on the diversity of species," Damschen said.

She and her colleagues report the finding in this week's issue of the journal Science.

Theory in Use

According to Damschen, conservationists popularized the theory of using corridors for species preservation in the 1960s and '70s.

"In the absence of experiments or studies to give knowledge to the conservationists, they embraced the theory," she said.

More than 800 organizations in the U.S. and Canada are now using corridors to create webs of protected habitat between Yellowstone National Park and the Yukon.

In India a 37-mile-long, 6-mile-wide (60-kilometer-long, 10-kilometer-wide) corridor connects important tiger habitats in the eastern Himalaya and the Western Ghats mountain ranges.

(Related news: "Tiger Habitat Plummeted 40 Percent in 10 Years, Survey Finds" [July 2006].)

In addition, conservationists in Chile's Bío Bío region are working to connect three established nature reserves with small private properties.

Pine Patches

Without scientific evidence showing that corridors work, the skeptics' arguments remained valid.

The Science study, Damschen said, is "the piece of scientific evidence that had previously been lacking."

The land Damschen and colleagues used for their experiment contained young longleaf pines, trees native to that part of South Carolina. Dense, mature pine plantations surrounded each experimental patch.

Each landscape was about the size of 12 city blocks and included a central patch of habitat with four surrounding patches.

One of the surrounding patches was connected to the central patch via a corridor.

The three remaining patches were of different shapes but equal in area to the connected patch plus its corridor.

Between 2000 and 2005 the researchers collected data on the diversity of plants in the patches.

Over time the connected patches grew about 20 percent more nonwoody plant species than the unconnected patches. The shape of the unconnected patches had no effect on their overall species diversity.

"We show that corridors are not simply an intuitive conservation paradigm. They are a practical tool for preserving biodiversity," Damschen and colleagues conclude in Science.

Corridor Confirmation

According to the researchers, corridors helped plant diversity by enhancing seed dispersal and pollination and by altering competition between plants.

"Plants were thought to be a fairly sedentary group of species, rooted in one place," Damschen said.

"It was unclear whether we'd see a response over five years … [but] we saw a very drastic change."

Stuart Pimm is a conservation biologist at Duke University in Durham, North Carolina, and a member of the National Geographic Society's Committee for Research and Exploration (National Geographic News is part of the National Geographic Society).

(Read a first person account from 2004 of Pimm's work in Brazil.)

"Corridors allow species to slosh from bad areas to good areas when the need arises," said Pimm, who was not involved in the research.

He said the latest finding is "experimental confirmation" that corridors really do work.

"And hugely important, they've done it on a scale that makes sense to people in the [U.S.] Forest Service and other agencies that have to do this sort of thing," he said.

The land managers can look at this experiment and say, "Aha, here we have a study that says even quite narrow corridors can be effective," he added.

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