An 18-year experiment that turned forests and farmland into a giant laboratory found that habitat corridors – thin connectors of land that link stretches of natural landscape – can significantly improve plant biodiversity and protect vulnerable species from extinction.
The evidence, described in Science, they suggest that expanding these corridors could be a useful strategy for preserving and restoring ecosystems in the country's shrinking wilderness areas.
All over the world, humans devour natural landscapes, felling trees for wood or clearing land to make way for agriculture, housing or commercial development. This habitat loss is a problem for the plants, animals and fungi that live in them, putting them at greater risk of threat and extinction. And that's bad news for everyone – including humans – because these ecosystems provide services we all need, such as water purification, carbon sequestration, and pollination of crops and other plants.
To improve the situation, humans cut much of the remaining land in isolated areas, further reducing the survival prospects of the species that live there. In southern California, for example, the highways divided the region's mountain lions into small, pure populations.
Plant species may also suffer. This is particularly true in longleaf pine savanna, an ecosystem that once covered about 92 million acres and it dominated most of the southeastern coast of Texas to Florida and to southern Virginia.
With an open cover structure, the undergrowth grasses and plants thrived alongside the trees, making the system rich in plant biodiversity. It is home to endangered species such as red-bearded woodpecker and endangered species such as gopher tortoise and the indigo snakeNot to mention many plant species unique to the ecosystem.
Native Americans have long managed the long-leaved pine savannah with periodic burns, complementing the low-intensity forest fires that were already part of and essential to ecosystem health. However, the mismanagement of European Americans – especially from the 1830s, when steam engines were extracting wood a more profitable company – finally reduced it to less than 3% of its original range.
What remains is often fragmentary. One potential solution, of course, is to expand these stretches by returning more land to nature. But this can be difficult to sell to farmers and other landowners.
Researchers have long explored another option: creating habitat corridors between these ecosystem fragments. This requires less land and still allows species to grow and spread, making it easier to resist unexpected surprises.
A long-term experiment at the Savannah River Site in South Carolina demonstrated the value of connecting isolated wilderness areas to habitat corridors. Video provided to The Times by Brad Herring.
But exactly how effective are these runners over time?
To discover, Ellen Damschen, a plant ecologist at the University of Wisconsin-Madison, and his colleagues set up a large-scale experiment at Savannah River Site in South Carolina. Historically, land was used for agriculture. Nuclear reactors were later built nearby to provide plutonium and tritium for nuclear weapons. Now a Department of Energy-owned nuclear reserve and managed by the US Forest Service, the site is slowly beginning to reforest.
In this mix of wild and abandoned land, Damschen's team set up 10 experimental long-leaf pine savanna fields, each containing four test samples measuring almost 14,000 square meters (about 3 square meters). 1/2 acres). Some patches were single rectangles, alone and without rope. Others were connected to another section by a thin corridor, 25 to 150 meters long. Other spots were still isolated, but they were half the length of a corridor on either side, like wings.
For 18 years, scientists have traveled through these sections every summer. They set up a grid in each area and counted all species in all squares of that grid. It was hard work, usually done in high humidity, while the heat index exceeded 100 degrees. For experienced biologists, surveying the 239 plant species in each area took about three hours, carrying liters of water on their backs.
"It's like an endurance sport," Damschen said. Then they used to eat ice cream.
The fine corridors between the larger spots were remarkably effective. Colonization rates – the rates at which species spread to new areas – were 5% higher in connected fragments than in non-attached fragments, and annual extinction rates were also 2% lower.
These differences may seem small, but have increased over time as interest on a savings account. After nearly two decades, there were 14% more species in the connected fragments than in the isolated ones, according to the report.
Connectivity can help for several reasons, Damschen said. With more freedom of movement, species can seek new resources, diversify their gene pool and recover if there is a local disaster in the area, to name a few benefits.
Researchers had expected biodiversity gains to level off at some point, but so far they have continued to rise.
"We were really surprised," said Damschen. "We have seen a continued positive increase in these positive runner benefits each year."
Sharon collinge, a University of Colorado Boulder ecologist who did not participate in the experiment, added that although there were other experiments involving habitat corridors, this was unique because it lasted so long and was performed on such a large scale.
"It's really an impressive long-term study that reveals something we didn't know before about how connectivity influences biodiversity," Collinge said.
Andrew Gonzalez, an ecologist at McGill University in Montreal, Canada, said the work strongly supports the creation of habitat corridors, especially in fragmented natural landscapes.
The result "is timely because the field is involved in a debate about the value of connectivity as a conservation strategy rather than simply protecting the area," said Gonzalez, who did not participate in the study. "Connectivity is a fundamental property of ecological systems and is crucial for maintaining diversity, especially in changing environments."
One of the next questions to answer is whether maintaining habitat corridors is more economical than acquiring large tracts of land, Collinge said.
"How do we use our dollars more efficiently?" She said.