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Habitat Corridors Increase Plant Diversity Over Decades

Researchers discuss their field work within the Savannah River Site Corridor Experiment. | Brad Herring

Reconnecting isolated fragments of once continuous habitats may be a powerful tool in restoring and preserving plant biodiversity worldwide, according to a new study published in the September 27 issue of Science.

According to the study results, the establishment of habitat corridors reduced the likelihood of plant extinctions by nearly 2% per year, while increasing the chances of colonization by new species by almost 5% per year. What's more, the positive effects continued to accrue over the entire duration of the study — a span of nearly 20 years — resulting in 14% more species in connected habitats compared to their isolated counterparts.

"We expected that the benefits might plateau, or even decrease, but we did not expect them to continue to accrue," said Ellen Damschen, the study's lead author and University of Wisconsin-Madison biologist. "After nearly 20 years, the positive impact of corridors on biodiversity has not slowed down."

The findings of the long-term study highlight the importance of habitat connectivity on plant colonization, survival and species richness by showing that restoration of habitat connectivity significantly increases plant species richness both annually and over decades. During a time of unprecedented global change and biodiversity loss, the results may provide an important silver lining in current conservation efforts focused on creating and maintaining habitat corridors.

Habitat fragmentation is most often a direct result of human activity. In many places across the globe, lands cleared for agricultural development or the building of cities and infrastructure are often stripped bare of the native flora and fauna. As a result, vast and contiguous habitats have been carved into smaller pieces, leaving many species marooned on isolated, island-like fragments separated by seas of farmland and concrete. Currently, 70% of Earth's forested area lies within a mile from a habitat's edge.

Habitat loss through fragmentation is among the greatest threats to biodiversity in ecosystems. This is particularly true for plants and other organisms that lack the mobility to colonize new areas or respond quickly to rapid ecological changes. As a result, very minor fluctuations in climate, for example, can be catastrophic — and a key driver for extinction — among these vulnerable species.

In light of this, efforts to restore habitat connectivity have become key in conservation strategies designed to minimize biodiversity loss and protect against species extinction. While ecological theory predicts the importance of connectivity in preserving and increasing species richness, the large-scale and long-term studies required to adequately understand habitat connectivity's role in shaping biodiversity are lacking.

Damschen and her colleagues manipulated connectivity by creating habitat corridors between otherwise isolated habitat fragments at the Savannah River Site in South Carolina, a threatened ecosystem within a global biodiversity hotspot, and closely monitored the corridors' impact on plant communities continuously for 18 years.

According to Damschen, the landscape-scale experiment allowed the researchers to untangle the effects of habitat reconnection from other factors such as habitat size or shape.

Typical studies of one to five years in length likely underestimate the impacts of long-term connectivity restoration, and their compounding benefits, on plant communities over several decades, the researchers said.

"In a world where so much habitat has been lost, corridors are a feasible, intuitive first step to conserve biodiversity," said Nick Haddad, co-author of the study.

Many habitat corridor like-features, such as urban greenways or forest buffers along rivers, are already being created without the benefits to biodiversity in mind. According to Haddad, conserving corridors can be a "win-win" for both people and nature.

While the study focuses on plants, Damschen, Haddad and their colleagues' research shows that corridors also impact other animal species, particularly pollinators like butterflies and bees, which could help explain why plants do better in connected patches, said Damschen.

"Conservation investments have trade-offs and our study suggests the time to start connecting habitat is now as it will pay off down the road," said Damschen. "Just like investing money in the bank with an annual, positive interest rate."