The world's endangered forests

Updated 9:34 AM ET, Fri September 4, 2015
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A new study led by Yale University estimates the Earth is home to 3 trillion trees -- more than 7 times greater than what was previously believed. But the study also estimates that the globe's tree population has been cut almost in half since the start of human civilization. Research shows that drought, insects and deforestation are decimating forests around the world. Nicolas Armer/AFP/Getty Images
Drought leaves trees more susceptible to disease, like these pines trees near Strawberry Valley in Utah. In the U.S., millions of acres of forest have been damaged by beetles, according to a report by the U.S. Global Change Research Program. Less severe winters and longer summers are allowing beetles to thrive. Ethan Miller/Getty Images/file
Riberalta, the largest town of Bolivia's Amazon region, is engulfed with fire during September 2005. The Amazon region saw widespread wildfires that turned the rainforest into a carbon source rather than a carbon sink. AIZAR RALDES/AFP/Getty Images/file
An area of forest in California killed off by pine beetles in 2003. David McNew/Getty Images/file
Forest fires engulfed more than 110,000 hectares across Russia during the summer of 2010. Here, a stand of charred birch and evergreen trees is filled with drifting smoke on the outskirts of the city of Voronezh. Alexey SAZONOV/AFP/Getty Images/file
Recent research suggests "the future broad-scale vulnerability of forests globally is being widely underestimated," said Craig Allen of the U.S. Geological Survey in August 2015. David McNew/Getty Images/file