Landscape corridors promote plant diversity

Landscape corridors thin strips of habitat that connect isolated patches of habitat are lifelines for native plants that live in the connected patches and therefore are a useful tool for conserving biodiversity.

That's the result of the first replicated, large-scale study of plants and how they survive in both connected patches of habitat those utilizing landscape corridors and unconnected patches. Scientists at North Carolina State University and collaborators at other U.S. universities conducted the study.

Patches of habitat connected by corridors contained 20 percent more plant species than unconnected patches at the end of the five-year study, says Dr. Ellen Damschen, the study's lead author and a postdoctoral researcher at the University of California, Santa Barbara. Damschen completed her Ph.D. in the lab of Dr. Nick Haddad, associate professor of zoology at NC State and a co-author of the paper describing the research.

The research appears in the Sept. 1 edition of the journal Science.

The loss and fragmentation of habitat is the largest threat to biodiversity globally, Damschen and Haddad say. In an effort to prevent species losses, conservation efforts have intuitively relied on corridors, which have become a dominant feature of conservation plans. However, there has been little scientific evidence showing that corridors do, in fact, preserve biodiversity.

To perform the research, the scientists collaborated with the U.S. Forest Service at the Savannah River Site National Environmental Research Park, a federally protected area on the South Carolina-Georgia border. Most of the Savannah River Site is covered with pine plantations. The U.S. Forest Service created eight identical sites, each with five openings, or patches, by clearing the pine forest. A central patch was connected to one other patch by a 150-meter-long, 25-meter-wide corridor, while three other patches were isolated from the central patch and each other by the surrounding forest. The patches are home to many species of plants and animals that prefer open habitats, many which are native to the historical longleaf pine savannas of this region.

The researchers surveyed all plant species inside connected and unconnected patches from 2000 to 2005; nearly 300 species of plants were found. When the study began, there was no difference in the number of species between connected and unconnected patches, the scientists say. After five years, however, patches with a corridor retained high numbers of species, while those without a corridor lost species.

Corridors provided the largest benefit to native species while having no effect on the number of invasive plant species. Invasive species seem to already be everywhere, not needing corridors for their spread, or remain where they originated, Damschen says. These results indicate that using corridors in conservation should provide benefits to native species that outweigh the risk of furthering the spread of exotic species.

Damschen says that a number of factors likely contributed to the difference in plant diversity. Seeds dispersed by animals are more likely to be deposited in patches with corridors; flowers are more likely to be pollinated because corridors increase the movement of insects; and animals that eat seeds like ants and mice can eat the seeds of more common species in connected patches and give rare seeds an advantage.

While the researchers predicted that corridors would be beneficial to increasing plant richness, "It's surprising that we would see such a dramatic change over a short time scale," Damschen says. "Plants are thought to be relatively sedentary organisms that are heavily influenced by their environmental surroundings. This study indicates that plants can change relatively quickly through their interactions with the landscape and the animals that interact with them, such as seed dispersers, pollinators and predators."

The next step in their studies of corridors is to make predictions for how corridors affect plants based on plant characteristics, Damschen and Haddad say. The researchers will study the specific effects of pollination and seed dispersal by wind and animals on plants in both connected and unconnected patches of habitat, for example.

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The study which included assistance from scientists at Iowa State University, the University of Washington, the University of Florida, and the University of California-Santa Barbara was funded by the National Science Foundation and by the Department of Energy-Savannah River Operations Office through the U.S. Forest Service Savannah River Institute. The U.S. Forest Service-Savannah River Site provided critical assistance with the creation and maintenance of the experimental landscapes.

Note to editors: An abstract of the paper follows.

"Corridors Increase Plant Species Richness at Large Scales"

Authors: Ellen I. Damschen, University of California, Santa Barbara and North Carolina State University; Nick M. Haddad, North Carolina State University; John L. Orrock, University of California, Santa Barbara; Joshua J. Tewksbury, University of Washington; Douglas J. Levey, University of Florida

Published: Sept. 1, 2006, in Science

Abstract: Habitat fragmentation is one of the largest threats to biodiversity. Landscape corridors, which are hypothesized to reduce the negative consequences of fragmentation, have become common features of ecological management plans worldwide. Despite their popularity, there is little evidence documenting the effectiveness of corridors at preserving biodiversity at large scales. Using a large-scale replicated experiment, we showed that habitat patches connected by corridors retain more native plant species than do isolated patches, that this difference increases over time, and that corridors do not promote invasion by exotic species. Our results support the use of corridors in biodiversity conservation.


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