Enlarge By David McNew, Getty Images Harvested trees in Sequoia National Forest are stacked July 2004 in an area burned during the massive McNally fire two years before in the Sierra Nevada Mountains of California. Man-made causes of forest loss include logging and wildfires caused by people. Natural causes would include natural wildfires and storm damage. Out of seven of the most heavily forested nations on Earth, the United States experienced a greater percentage of forest loss from 2000 to 2005 than did any of the other countries, a study said Monday. The United States lost more than 46,000 square miles of forest in those years, a size roughly equivalent to the state of Pennsylvania. That's about 6% of the nation's forested land. GREENEST BUILDINGS: Architects pick 2010 winners EPA: Climate plan calls for forest expansion LATEST: Earth Day and other environmental news "That's the most of the seven countries that have over 1 million square kilometers of forest," says study lead author Matthew Hansen of South Dakota State University. Worldwide, researchers determined that the globe lost forest cover of nearly 400,000 square miles — roughly 3% of the world's forested areas — during the first half of the last decade. The other countries in the study were Canada, Russia, China, Brazil, Indonesia and the Democratic Republic of the Congo. The study, which appears in the Proceedings of the National Academy of Sciences, found that the forest loss was the result of both human and natural causes. "We do not quantify what the causes are, and we do not quantify how much forest gain there was from 2000 to 2005," Hansen says. "But clearly, industrial harvesting/clearing is very important." Man-made causes of forest loss include logging and wildfires caused by people. Natural causes would include natural wildfires and storm damage. The one part of the contiguous USA that experienced the most forest loss was the Southeast, a large chunk of which lost more than 10% of its forest cover from 2000 to 2005, the year for which the most recent data were available. Hansen points out that the forest loss in the USA isn't necessarily permanent: "This does not mean that (the forests) do not regenerate, and we make no statements whatsoever about sustainability," he says. "But, compared to other regions of the world, a lot is going on." The first of its kind, the study used satellite images to measure forest loss around the world. Hansen says much more study in the area is needed as improvements are made in satellite technology and accessibility. "We need to be more ambitious," he says. "If we had an improved monitoring capability, you could imagine a daily 'land report,' akin to weather, where fires, floods, crop emergence, new forest clearing, new construction are quantified." Guidelines: You share in the USA TODAY community, so please keep your comments smart and civil. Don't attack other readers personally, and keep your language decent. Use the "Report Abuse" button to make a difference. You share in the USA TODAY community, so please keep your comments smart and civil. Don't attack other readers personally, and keep your language decent. Use the "Report Abuse" button to make a difference. Read more