Biodiversity beyond the habitat's borders

Recently, images of melting sea ice and shrinking rainforests have highlighted the world's biodiversity crisis and made us aware of the need to find a balance between preserving natural ecosystems while still having enough land for human use.

"About 10 percent of the world's land surface is afforded formal protection. We need to manage that 10 percent as best as we possibly can to preserve biodiversity but also be mindful of human needs, such as food and fiber production," said Lars A. Brudvig, Ph.D., post-doctoral researcher in biology in Arts & Sciences at Washington University in St. Louis.

"One way to do this is by managing the land in a way that promotes biodiversity beyond the habitat's borders."

One of the most popular ways to manage landscapes fragmented by humans is to connect the isolated patches of habitat with skinny strips of land called corridors.

Brudvig and Ellen I. Damschen, Ph.D., assistant professor of biology at Washington University, in collaboration with researchers at the University of Washington, North Carolina State University and University of Florida, have discovered that the biodiversity in a patch of habitat can extend outside the borders of a protected area; this effect is magnified when the habitats are connected by corridors.

Their findings provide a strategy for managing nature preserves to maximize biodiversity in the small spaces that are already formally protected.

Throughout the Southeast, most of the historically predominant ecosystem — longleaf pine Savanna — has been destroyed and converted into pine plantation forests to provide resources for human use. As a result, there is a great deal of interest in conserving the three percent of habitat that remains and in restoring additional habitat.

In order to determine what role habitat connectivity might play in habitat conservation and restoration practices, the USDA Forest Service-Savannah River created eight experimental landscapes in 2000, each with five open patches in the pine plantation forest near Aiken, S.C.

Within each landscape, two of the five patches were connected by a corridor and the remaining three were left isolated. Today, this is the location of the world's largest experimental test of corridors and one of the world's largest habitat fragmentation experiments.

"We are restoring these patches for longleaf pine savanna with prescribed fire and longleaf pine seedling transplants. We previously found that patches connected by corridors have acquired more species of plants, or higher biodiversity, than isolated patches," Brudvig explained.

In this study, published online in the Proceedings of the National Academy of Sciences the week of May 18, 2009, the researchers looked at the species of plants growing outside the protected longleaf pine savanna patches. The title of their paper is "Landscape Connectivity Promotes Plant Biodiversity Spillover Into Non-target Habitats."

In patches that were connected by corridors, more species of plants native to the pine savanna were found in the surrounding pine plantation forest, than around isolated patches.

"Because corridors promote higher levels of biodiversity in target patches, this bleeds over and elevates the biodiversity in the non-target habitat, increasing the area receiving a benefit from corridors by 160 percent," Brudvig said.

"Because of this spillover effect, the biodiversity benefit provided by corridors is more than double what we thought before," he said. "This is quite a large and pronounced effect."

The concept of spillover originates from marine fisheries management. In seas with protected areas, the total fish catch is higher than in seas where fishing is not restricted. In the protected areas, fish populations grow until the excess density spills over into the surrounding waters, where fishing is allowed.

"We borrowed a concept that focused on single or small sets of species and put it into a biodiversity context to ask questions about all species that live in one ecosystem," Brudvig said.

The research was funded by the National Science Foundation. The USDA Forest Service-Savannah River maintains the landscape with prescribed fires and other management activities.

These results apply directly to preserving biodiversity native to longleaf pine savanna.

"Throughout the Southeast, this provides a management strategy to promote a rare ecosystem and afford biodiversity benefits within a managed landscape," Brudvig said.

However, their findings have implications for habitats around the globe as well.

"We literally live in world of fragmented habitats, where the habitats that do remain are scattered around and intermixed with non-target habitats. It is entirely possible that this biodiversity spillover effect might be happening in a variety of ecosystems all over the world," Brudvig said.

"Through management activities, such as building corridors, we might be able to promote this spillover effect elsewhere."