Earth’s Forests Are Broken

Researchers find that critical forest habitats around the world have become increasingly fragmented, putting plants and wildlife (not to mention the planet) at risk.

A forest fragmentation study called the Savannah River Site Corridor Experiment examines how ecosystems degrade on the edges of forests. (Photo: Ellen Damschen)

Mar 25, 2015· 2 MIN READ
John R. Platt covers the environment, wildlife, and technology and for TakePart, Scientific American, Audubon, and other publications.

Imagine, if you will, a forest on the edge of a parking lot.

That first line of trees next to the concrete isn’t very healthy, is it? The plants are scraggly, oddly spaced, and choked off by pollution from the cars that come and go all day long. The ground beneath them is dry, partially barren, and strewn with litter and detritus. No birds or other wildlife can be seen.

Now, imagine those unhealthy conditions extrapolated to every other forest on the planet.

Finally, imagine that this is reality. You won’t be that far off from the actual condition of Earth’s forests, which, according to a powerful new study, have become increasingly fragmented from one another in a way that threatens not only what lives in the forests but everything that lives around them.

The study, published this week in the journal Science Advances, brought together two dozen scientists who have been studying habitat fragmentation around the globe. It not only condenses the researchers’ individual observations from experiments conducted over the past 30 years; it also uses advanced satellite data to look at the state of the world’s forest habitats.

The results aren’t good.

“Whenever you’re in a forest anywhere on the face of the Earth, there’s a one in five chance that you’re within a football field’s length of the edge of the forest,” said the study’s lead author, Nick Haddad, a biology professor at North Carolina State University. “And there’s a three out of four chance that you’re within a kilometer of the edge. That’s just a few city blocks. I’m looking out my office window right now, and I can see a kilometer. That’s not that far.”

This fragmentation has a wide range of effects, not just on the forests but also on the entire ecosystem. Animal and plant species first become locked into smaller habitats, and then many of them disappear. Pollination in the area diminishes, affecting flowers and other plants directly outside the forests. The ground near the edges of the forests becomes less able to absorb nutrients, causing further plant loss.

These diminished forests also lose much of their ability to sequester carbon, which slows climate change, Haddad said. Losing even small regional habitats could collectively have a lasting global impact.

Not least, the destruction of forests makes it harder to escape into nature and get away from it all. Haddad said the forests that exist are so fragmented and so close to the noise of civilization that few can truly be called wilderness.

Some of these effects are almost immediate; others take five or 10 years—or much longer—to materialize.

“Fragmented habitats degrade over time,” Haddad said. “It’s a downward trajectory that we can measure over a period of decades.”

The paper calls this “extinction debt”—the delayed loss of species in a habitat following its fragmentation. In their experiments, the researchers found that the number of species within a fragmented habitat drops by 20 percent or more after the first year. After a decade, that increases to more than 50 percent.

It’s not just the big, noticeable, “charismatic” species that suffer. “It’s the entire breadth of plants and animals—the diversity of life—that is affected by habitat fragmentation,” Haddad said.

Although he warned that “we do not know the end to what fragmentation will be,” Haddad said there are possible solutions. Those include establishing connecting corridors to link isolated habitats, conserving more land, and establishing new ways to improve agricultural efficiency so we don’t need to keep cutting down forests to feed Earth’s ever-growing human population.

But as the paper warns, much of the planet’s remaining forest fragments are already smaller than 25 acres. With agricultural land expected to grow another 18 percent by 2050 and the size of the urban population expected to triple by 2030 (according to sources cited by the paper), that doesn’t leave much room for the forests Earth will need for centuries to come.