Can a forest that exists only in the spaces between roads and patches cleared for human settlement and agricultural development truly be called a forest?
Not so much, say researchers studying the growing, global problem of forest fragmentation. And the "persistent, deleterious and often unpredicted" consequences of human activity, finds a new study conducted by a team off 24 international scientists, and funded by the National Science Foundation, may be ruinous for plant and animal life.
“There are really only two big patches of intact forest left on Earth -- the Amazon and the Congo -- and they shine out like eyes from the center of the map,” lead author Nick Haddad, a professor at North Carolina State University, told the New Yorker.
"Nearly 20 percent of the world's remaining forests are the distance of a football field -- or about 100 meters -- away from forest edges," he elaborated in a statement. "Seventy percent of forest lands are within a half-mile of forest edges. That means almost no forests can really be considered wilderness."
And the consequences of that forest loss, the researchers discovered, may be more profound than we've previously realized. To figure that out, they looked at the results of seven experiments, which took place on five different continents, that aimed to simulate the impacts of human activity on forests. Several of the studies have been going on for decades, and the results, in aggregate, were striking: fragmented habitats, they found, can reduce plant and animal diversity by anywhere from 13 to 75 percent.
In general, the studies showed that when patches of forest become smaller and more isolated, the abundance of birds, mammal, insects and plants decreases in kind -- those pressures, the authors write, reduced the species' ability to persist. Areas surrounded by a higher proportion of edges, they also found, were a boon to predators that target birds, which is arguably good, in the short-term, for the predators, although not so much for the birds. Fragmented forests experienced a decline in their core ecosystem functions, as well: they were less able to sequester carbon dioxide, an important element of mitigating climate change, and displayed reduced productivity and pollination.
"No matter the place, habitat or species," said study co-author Doug Levey, a program director in NSF's Division of Environmental Biology, said, "habitat fragmentation has large effects, which grow worse over time."
That second part is important: the authors emphasize that in many cases, the harmful impacts of fragmentation on forest ecosystems only become apparent after many years. On average, they found, fragmented forests lose more than half of their species within just 20 years; in the one experiment that's still ongoing after more than two decades, the losses are continuing to compound. As such, they write, "the effects of current fragmentation will continue to emerge for decades" -- we still haven't seen the full extent of what our slicing and dicing of the forests has wrought.
Appreciating the full extent of the damage, the authors argue, necessitates considering the options for doing something about it. Haddad suggests several options, from stepping up conservation efforts to finding ways to increase agricultural efficiency. William Laurance, a professor at Australia's James Cook University and another of the study's co-authors, has his eyes on roads, which break up habitats while introducing poachers, miners, loggers and other destructive human forces.
"The trouble is that, for humans, if not for plants and animals, roads are useful," the New Yorker points out the obvious. And current trends suggest we're on track to pave more of these destructive edges: more than fifteen million new miles worldwide, according to the International Energy Agency. That's the kind of thing, according to Laurence, that "scare[s] the hell out of ecologists."