The Serengeti looks much like it did hundreds of years ago.
Lions, hyenas and other major predators still lurk herds of wildebeest over a million strong people, preventing them from eating too much vegetation. This diversity of trees and grasses supports dozens of other species, from the lively green-orange Fischer birds to the beetles. In turn, these species carry seeds or pollen through the plains, allowing the plants to reproduce. Humans are there too, but with relatively low densities. Overall, it’s an excellent example of what biologists call an ecologically intact ecosystem: a moving tangle of complex relationships that together sustain a rich diversity of life, without us.
Such places are rarely gone.
The vast majority of the Earth’s Earth (an astonishing 97 percent) no longer qualifies as ecologically intact, according to a comprehensive study of Earth’s ecosystems. Over the past 500 years, too many species have been lost or reduced in number, researchers report April 15 in Frontiers in Forests and Global Change.
Of the few fully intact ecosystems, only about 11 percent are within existing protected areas, the researchers found. Much of this virgin habitat exists in the northern latitudes, in the boreal forests of Canada, or in the tundra of Greenland, which are not full of biodiversity. But pieces of rainforests rich in species from the Amazon, Congo and Indonesia also remain intact.
Sign up to receive the latest from Science News
Headlines and summaries of the latest Science News articles, delivered in your inbox
“These are the best of the best, the last places on Earth that have not lost any species we know of,” says Oscar Venter, a conservation scientist at the University of North British Columbia in Prince George who did not participate in the study. Identifying these places is crucial, he said, especially for threatened development regions that require protection, such as the Amazon rainforest.
Conservation scientists have long tried to map how much of the planet remains undamaged by human activity. Previous estimates using satellite imagery or raw demographics found between 20 and 40 percent of the planet were free of obvious human incursions, such as roads, light pollution or the huge scars of deforestation. But an intact forest canopy can hide an emptied ecosystem beneath.
“Hunting, the impacts of invasive species, climate change, can damage ecosystems, but they cannot be easily perceived by satellite,” says conservation biologist Andrew Plumptre of Cambridge University. A Serengeti with fewer lions or hyenas (or none) may appear intact from space, but key species that help the entire ecosystem function are missing.
What exactly constitutes a fully intact and functional ecosystem is diffused and debated by environmentalists, but Plumptre and his colleagues began looking for habitats that would conserve their entire entourage of species, in their natural abundance from 1500 AD. Nature Conservation is used to assess species extinctions, although humans alter ecosystems by killing large mammals for thousands of years (SN: 26/08/15).
Large strips of land are needed to support wide-ranging species. Thus, the researchers initially considered only areas larger than 10,000 square miles, roughly the size of Puerto Rico. The team combined existing habitat intact datasets with three different assessments of where species were lost, covering some 7,500 animal species. Although 28.4 percent of land of more than 10,000 square miles is relatively free of human disturbances, only 2.9 percent has all the species it did 500 years ago. Decreasing the minimum size of the included area to 1,000 square miles increases the percentage, but barely, to 3.4.
Simply retaining species is not enough for ecological intact, as a diminished number of key players could throw the system out of the coup. Researchers have accounted for the population density of just over a dozen large mammals whose collective areas span much of the globe, including gorillas, bears and lions. Plumptre admits that this aspect is narrow, but large mammals play important ecological roles. They also have the best historical data and are often the first to be affected by human incursion. Given the declines in large mammals only slightly decreased the percentage of ecologically intact land, to 2.8 percent.
Overall, the account of ecologically intact land “was much lower than we expected,” Plumptre says. "Going in, I guessed it would be 8 to 10 percent. It just shows the huge impact we've had."
Both Venter and Jedediah Brodie, a conservation ecologist at the University of Montana in Missoula, question whether the authors were too strict in their definition of ecological intact.
“Many ecosystems around the world have lost one or two species but they are still vibrant and diverse communities,” Brodie says. A decline of a few species may not mean a disaster for the entire ecosystem, as other species may fall to fulfill those functions.
Still, the study is a valuable first look that shows us “where the world looks 500 years ago and gives us something to point out,” Plumptre says. It also identifies mature areas for restoration. Although only 3 percent of the land is currently ecologically intact, the introduction of up to five lost species could restore 20 percent of the land to its former glory, the researchers calculate.
Species reintroductions have worked well in places like Yellowstone National Park, where wolf restoration has re-balanced the ecosystem (SN: 21/07/20). Those schemes may not work everywhere. But while the world community discusses how to protect nature over the next decade (SN: 22/04/20), Plumptre hopes this study will encourage policymakers to “not only protect the land that exists, but also think about restoring it to ser ".