Changes in world's forests portrayed in high definition

Published on: Nov 15, 2013

A new study based on Earth-observing satellite data comprehensively describes changes in the world's forests from the beginning of this century. Published in Science Nov. 14, this unparalleled survey of global forests tracked forest loss and gain at the spatial granularity of an area covered by a baseball diamond (30-m resolution).

Led by Matthew C. Hansen of the University of Maryland and assisted by U.S. Geological Survey (USGS) co-author Thomas R. Loveland, a team of scientists analyzed data from the Landsat 7 satellite to map changes in forests from 2000 to 2012 around the world at local to global scales. The uniform data from more than 650,000 scenes taken by Landsat 7 ensured a consistent global perspective across time, national boundaries, and regional ecosystems.

"Tracking changes in the world's forests is critical because forests have direct impacts on local and national economies, on climate and local weather and on wildlife and clean water," said Anne Castle, assistant secretary of the interior for water and science. "This fresh view of recent changes in the world's forests is thorough, objective, visually compelling and vitally important."

Overall, the study found that from 2000 to 2012 global forests experienced a loss of 888,000 square miles, roughly the land area of the U.S. states east of the Mississippi River. During the study period, global forests also gained an area of 309,000 square miles, approximately the combined land area of Texas and Louisiana, USGS said.

The global survey found that Russia experienced the most forest loss overall (in absolute numbers) over the study period. Brazil was the nation with the second-highest level of forest loss, but other countries, including Malaysia, Cambodia, Cote d'Ivoire, Tanzania, Argentina and Paraguay, experienced a greater proportional loss of forest cover. Indonesia exhibited the largest increase in forest loss; its losses on an annual basis during 2011-12 were twice what they were during 2000-03.

USGS said Brazil is a global exception in terms of forest change during this timeframe, with a dramatic policy-driven reduction in the rate of deforestation in the Amazon Basin. Brazil's use of free Landsat data in documenting trends in deforestation was crucial to its policy formulation and implementation. To date, only Brazil produces and shares spatially explicit information on annual forest extent and change, USGS explained.

In the U.S., the most intensive forest change was noted in the southeastern states where pine plantations allow for cyclic tree harvesting for timber, followed by immediate planting of tree replacements. In this area, more than 30% of the forest cover was either lost or regrown during the study period.

Deforestation as well as deliberate forest regrowth are human factors that accounted for most of the forest change. Natural forces — for instance, wildfire, windstorms, insect infestations and regrowth of abandoned agricultural areas — also caused forest changes, which were also methodically mapped.