Worldwide Loss of Interior Forest

Researchers look beyond the numbers to see the true impacts of global forest loss

by Stephanie Worley Firley, EFETAC
A 2010 aerial photo of land near Hiram, Georgia, overlaid with color represents spatial patterns based on global tree cover data. Tree cover as of 2012 is shown in transparent green; tree cover loss from 2000 to 2012 is shown in transparent blue. Photo courtesy of National Agriculture Imagery Program.

A 2010 aerial photo of land near Hiram, Georgia, overlaid with color represents spatial patterns based on global tree cover data. Tree cover as of 2012 is shown in transparent green; tree cover loss from 2000 to 2012 is shown in transparent blue. Photo courtesy of National Agriculture Imagery Program.

Between 2000 and 2012, the world lost forest area and gained forest area. But the losses exceeded the gains, according to U.S. Forest Service researchers and partners who compared tree cover data from those years and estimated a global net loss of 1.71 million square kilometers of forest — an area about two and a half times the size of Texas. That’s only part of the story, though.

“In addition to the direct loss of forest, there was a widespread shift of the remaining global forest to a more fragmented condition,” says Kurt Riitters, a research ecologist and team leader with the Eastern Forest Environmental Threat Assessment Center and the lead author of a study describing the phenomenon, recently published in the journal Landscape Ecology. “Forest area loss alone underestimates ecological risks from forest fragmentation. The spatial pattern of forest is important because the same area of forest can be arranged in different ways on the landscape with important consequences for ecosystem processes.”

To understand where risks from forest fragmentation might be greatest, the researchers evaluated the loss of interior forest — core areas that, when intact, maintain critical habitat and ecological functions. (In contrast, non-interior forest edge areas are subject to impacts from invasive species, pollution, and variation in soil moisture, for example.) Using global tree cover data, researchers mapped the forests of 2000 and 2012 and examined the patterns of change across ecological regions and biomes. Their analysis revealed a net loss of 3.76 million square kilometers of interior forest area, or about ten percent of interior forest — more than twice the global net loss of forest area. The rate at which interior forest area was lost was more than three times the rate of global forest area loss.

All forest biomes experienced a net loss of interior forest area during the study period. Across the globe:

  • Temperate coniferous forests experienced the largest percentage of loss,
  • Tropical and subtropical moist broadleaf forests lost the most area of interior forest, and
  • Boreal forests and taiga lost interior forest at the highest rate.

Researchers note that the reasons for losses, and therefore the consequences, depend on local circumstances. Human activities and land use changes that result in permanent deforestation have a much greater impact than temporary deforestation from natural disturbances, such as a fire.

Monitoring remains an important tool to provide early warnings of forests at risk of reaching a tipping point, and the results of this study can inform and focus conservation and management decisions in areas of concern. “As forest area is lost and the remainder becomes more fragmented, the remaining forest may no longer function as interior forest,” explains Riitters. “Sustaining forest interior is arguably as important as sustaining forest itself.”

The study’s coauthors include James Wickham, U.S. Environmental Protection Agency; Jennifer Costanza, North Carolina State University/Eastern Threat Center; and Peter Vogt, European Commission Joint Research Centre.

Read the full text of the article.

For more information, email Kurt Riitters at kriitters@fs.fed.us.

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