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Species spillover: Broadening benefits of habitat corridors

pine,trees,savannas,biodiversity,corridorsAnimals are born to roam. So when they find themselves living on small patches of land surrounded by housing developments or cornfields, their movement is unnaturally confined. They may never find that other patch a mile down the road that is full of food, nesting grounds, even mates with differing genes (a very good thing for the health of a species.) What’s more, the plant seeds and pollen that naturally hitchhike with them are also stuck.

But, as conservationists discovered more than 40 years ago, if you connect these fragments with skinny strips of natural land, called “corridors,” plants and animals can more naturally spread. Now, results published online last week in the Proceedings of the National Academy of Sciences suggest the strategy’s benefits for biodiversity may even extend beyond the borders of these linked patches of land.

“The spillover effect with corridors gives a larger conservation bang for the buck,” said study co-author Nick Haddad, associate professor of biology at North Carolina State University, in a statement. His team found that adding habitat corridors more than doubled the resulting area of improved plant biodiversity.

As human populations grow, so do the spatial and social roadblocks to establishing new conservation areas. That leaves creating pathways between currently safeguarded spaces especially valuable. While only about 10 percent of land around the world is protected, says the study’s lead author, Lars Brudvig, a post-doctoral student at Washington University in St. Louis, “this gives hope for the remaining 90 percent that is not afforded formal protection.”

The researchers borrowed the idea from marine fisheries management. Banning fishing in over-exploited areas allows populations to recover, increasing their density to the point that they spill over into surrounding, fishable waters. As a result, says Brudvig, marine protected areas “support higher fish catches overall compared to where fishing is allowed everywhere.”

In the world’s largest corridor experiment, Brudvig, Haddad and colleagues translated this technique from the marine into the terrestrial, and beyond a small subset of species to an entire ecosystem. Within each of eight experimental pine plantation forests, they manipulated five fragments of land opened for the regrowth of native species: two they connected with corridors, the other three they left alone.

For connected fragments, increases in native plant biodiversity extended for about 30 percent of the width of the original one hectare (one percent of a square kilometer). These results may not apply to fragments of all shapes and sizes, but the “vast majority of protected areas across the world are not large at all,” says Brudvig. “Our findings may translate directly to smaller reserves.”

And within this study’s South Carolinian site, the effects could be significant. Before humans began converting land into plantations, longleaf pine savannas thrived in the southeastern United States. What’s left of these native landscapes remain “hotspots of biodiversity” and “host many species not found anywhere else in the world,” says Brudvig. “By promoting them, we are - in some cases - staving off extinctions.”

Image ©iStockphoto.com/Maliketh

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