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Humans Have Altered 97 Percent of Earth’s Land Through Habitat and Species Loss

The study, which did not include Antarctica, also identified opportunities to restore up to 20 percent of land ecosystems

Smoke lingers following fires in the Brazilian Amazon rainforest in August 2020. (Photo by Ernesto Carriço/NurPhoto via Getty Images)
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A study published on April 15 in the journal Frontiers in Forests and Global Change presents evidence that only about three percent of Earth’s land ecosystems remain untouched by human activity.

The analysis focuses on large swaths of land, about 3,860 square miles each, to account for the amount of habitat required by wide-ranging species. The study takes into account three measures of ecological integrity: habitat intactness, which is how human activity has affected the land; faunal intactness, which looks at species loss; and functional intactness, which focuses on species loss among animals that contribute to the health of an ecosystem.

The latter two points measure on-the-ground impacts that couldn’t be assessed with satellite images and demographic data alone, which is how previous studies had looked at human impact, Jonathan Lambert reports for Science News. The new study also shows up to 20 percent of affected ecosystems could be restored to their pre-industrial health with the reintroduction of five or fewer important species.

“Conservation of intact ecosystems is critical for the maintenance of biodiversity on Earth, and in turn for the services that these ecosystems provide to humans,” says Smithsonian Environmental Research Center ecologist Kimberly Komatsu, who was not involved in the study, to New Scientist’s Krista Charles.

Most of Earth’s undamaged ecosystems are in the northern tundra, like Canada and Greenland. But pockets of wild, unchanged habitat remain in Indonesian rainforests and the Amazon rainforest, as well as the Congo basin. Only 11 percent of the intact ecosystems are protected wildlife areas, although many are instead under the management of indigenous communities “who have played a vital role in maintaining the ecological integrity of these areas,” the researchers write in the study.

The researchers began with existing datasets that measured habitat intactness, and then combined that information with data showing where about 7,500 animal species had been lost. While about 28 percent of land habitats are intact, only about 2.9 percent of ecosystems have all the animal species that they did 500 years ago.

To measure functional intactness of the ecosystems, the researchers analyzed the populations of about a dozen large mammals that play important roles on their home turf. When changes to their populations were factored into the analysis, the results showed that just 2.8 percent of land ecosystems remain intact.

This result “was much lower than we were expecting,” says University of Cambridge conservation biologist Andrew Plumptre to Science News. “Going in, I’d guessed that it would be 8 to 10 percent. It just shows how huge an impact we’ve had.”

Plumptre tells Science News that the decision to focus on large mammals was a narrow measure of whether an ecosystem has everything it needs to function. University of Montana conservation ecologist Jedediah Brodie, who was not involved in the research, tells Science News that the analysis may have been too strict in defining an intact ecosystem, because sometimes if one species disappears, another one can fill its niche.

But some animals have a key role that can’t be replaced, like dispersing seeds of the plants that they eat, or regulating the number of prey animals in an environment.

"When these are removed, the dynamics can vary and can sometimes lead to ecosystems collapsing,” says co-author and conservation biologist Daniele Baisero of the Key Biodiversity Areas Secretariat to CNN’s Laura Smith-Spark. “The reintroduction of these species can return a balance to the ecosystem."

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