March 26th, 2015 by Sandy Dechert
When environmentalists, farmers, and loggers speak about forests, the discussion usually revolves around the issue of deforestation, which is one of the largest contributors to climate change. As James Ayre pointed out in a recent PlanetSave article, forest cover estimates are currently a subject of hot debate because a new satellite imaging study contradicts the slightly positive forest estimates in the United Nations Food and Agriculture Organization’s Forest Resource Assessment. Another important issue came to the forefront last Friday, though, with a study by Nick Haddad of North Carolina State University and over 20 international coauthors in the journal Science Advances.
Dr. Haddad notes:
“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.”
The National Science Foundation funded the study.
Haddad’s research confirms that more than 70% of the world’s forest area now lies within about a half-mile (one kilometer) of the forest edges, and that no matter what the ecosystem (forest, prairie, patch of moss), habitat destruction causes an average of 50% of the indigenous plant and animal species to disappear within 20 years.
Biodiversity dwindles from fragmentation. The core ecosystems of fragmented forests decline, and their ability to sequester carbon dioxide goes with them, as do productivity and pollination. Some fragmented areas continue to lose species for 30 years or more.
From the published abstract:
“A synthesis of fragmentation experiments spanning multiple biomes and scales, five continents, and 35 years demonstrates that habitat fragmentation reduces biodiversity by 13 to 75% and impairs key ecosystem functions by decreasing biomass and altering nutrient cycles. Effects are greatest in the smallest and most isolated fragments, and they magnify with the passage of time. These findings indicate an urgent need for conservation and restoration measures to improve landscape connectivity, which will reduce extinction rates and help maintain ecosystem services.”
As Michelle Nijhuis pointed out in the New Yorker last weekend, roads—necessary for communication and industrial development—have caused most of the world’s forest fragmentation problems. You can see their extent on this estimate of worldwide forest fragmentation. And many are very new—it was less than half a century ago that people cut the first paved highway across the Brazilian Amazon.
According to International Energy Agency estimates, between now and 2050, more than fifteen million more miles of paved roads will be built. Coauthor William F. Laurance of Australia’s James Cook University and his colleagues were able to publish an Amazon forest map in the journal Nature late last year that indicates both areas to avoid and those where new roads could increase food production without causing extensive environmental harm.
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