A NEW study based on Earth-observing satellite data comprehensively describes changes in the world's forests from the beginning of this century.
According to a Nov. 14 announcement of the results, this survey of global forests tracked forest losses and gains at the spatial granularity of an area covered by a baseball diamond (30 m resolution).
A team of scientists, led by Matthew C. Hansen of the University of Maryland and assisted by Thomas R. Loveland with the U.S. Geological Survey (USGS), 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, forests around the world 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, followed by Brazil. Other countries such as 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 time frame, with a dramatic policy-driven reduction in the rate of deforestation in the Amazon Basin. Brazil's use of free Landsat data to document trends in deforestation played a crucial role in its policy formulation and implementation. To date, only Brazil produces and shares spatially explicit information on its 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 methodically mapped as well.
"Ever since USGS made Landsat data free to anyone in 2008, Landsat imagery has served as a reliable common record, a shared vocabulary of trusted data about Earth conditions," Castle said. "It's been said that the free data policy is like giving every person on the globe a free library card to the world's best library on Earth observations."
Tom Loveland, chief scientist at the USGS Earth Resources Observation & Science Center and a co-author of the study, added, "With the free data policy, we have seen a remarkable revolution in the use of Landsat for documenting the changes in the Earth's land cover. This multi-organization project was only feasible with the existence of free Landsat data."
The research team included scientists from the University of Maryland, USGS, Google, the State University of New York, Woods Hole Research Center and South Dakota State University. The collaborative study was published in the Nov. 15 issue of Science.
Since 1972, the Landsat program has played a critical role in supplying continuous, objective data that can be used to monitor, understand and manage the resources needed to sustain human life, such as food, water and forests.