Satellite Study Covers Forest Loss Worldwide

Released: 5/6/2010 8:40 PM EDT
Source Newsroom: South Dakota State University
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Citations Proceedings of the National Academy of Sciences (PNAS)

Newswise — A new study using satellite imagery finds the greatest loss in forest cover from 2000 to 2005 wasn’t in rain forests, but in boreal forests in places like North America.

Despite ongoing threats to rain forests in the Amazon and Congo river basins and in Indonesia, losses were greatest in those boreal forests, followed by humid tropical, dry tropical and temperate forests.

“This study quantifies all stand-replacement disturbances regardless of land use,” said South Dakota State University professor Matt Hansen, co-director of SDSU’s Geographic Information Science Center of Excellence.

“Human disturbances, such as clear-cuts in managed forests and deforestation, as well as natural disturbances such as fire, disease and storm damage, are all included. What we found was a widely varying dynamic across the globe’s forests.”

Hansen was lead author of the study, “Quantification of global gross forest cover loss,” which appeared online on April 26, in the Proceedings of the National Academy of Sciences. Hansen’s co-authors were Peter Potapov, also of SDSU’s Geographic Information Science Center of Excellence, and Stephen Stehman, of the College of Environmental Science and Forestry at State University of New York in Syracuse.

Using images from two satellite-based sensors, the study tracked gross forest cover loss, or GFCL, defined as the area of forest cover removed because of any disturbance, including both natural and human-induced causes.

The study found North America has the greatest area of gross forest cover loss, followed by Asia and South America. North America alone accounts for nearly 30 percent of global GFCL and features the highest proportional GFCL of 5.1 percent. Africa has the lowest proportional GFCL of 0.4 percent, reflecting a lower overall use of forests for commercial development.

Combined, North and South America account for more than one-half of the global total area of GFCL. South America has the largest remaining intact forests within the Tropics, areas that are under increasing pressure from agro-industrial development. North America features a spatially pervasive GFCL dynamic with logging and fire as primary causes.

Nationally, Brazil lost the largest area of forest over the study period — 165,000 square kilometers or about 64,000 square miles — followed by Canada at 160,000 square kilometers, or about 62,000 square miles. Of the countries with more than one million square kilometers of forest cover, the United States showed the greatest proportional loss of forest cover and the Democratic Republic of Congo showed the least.

The United States includes both temperate forests and, in Alaska, boreal forest cover. It showed the highest percentage of year 2000 GFCL (6.0 percent). Although fire is a major contributor, particularly in Alaska and the western part of the country, logging is a primary and widespread cause of GFCL. Regional centers of logging are found mainly in the southeastern states, but also along the West Coast and in the Upper Midwest.

Hansen cautioned that gross forest cover loss is only one component of net change, and that the processes driving forest loss and recovery differ by region. Those are areas future research can explore.

“For example, the majority of estimated gross forest cover loss for the boreal biome is due to a naturally induced fire dynamic. To fully characterize global forest change dynamics, remote sensing efforts must extend beyond estimating gross forest cover loss to identify proximate causes of forest cover loss and to estimate recovery rates,” Hansen said.

Nearly 60 percent of the boreal forest cover lost is due to fire, Hansen said, while the remaining 40 percent of loss in boreal forests is attributable to logging and other change dynamics such as insect and disease pressure. For example, mountain pine beetle infestations are an important factor in loss of forest cover in British Columbia, Canada.

The study looked specifically at the seven nations of the world that have more than one million square kilometers of forest cover. The Russian Federation has the most extensive forest cover, followed by Brazil, Canada, the United States, the Democratic Republic of Congo, China and Indonesia.

Those seven countries account for more than 57 percent of the world’s forests.


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