The U.S. Forest Service estimates 6.3 billion dead trees were still standing in 11 Western states in 2015, up from 5.8 billion in 2010.

The numbers come from the agency’s annual Forest Inventory Analysis Program and include trees at least 5 inches (127 millimeters) in diameter.

The agency estimates roughly 20 percent of the standing dead trees in 2015 were killed by bark beetles. Other causes of death include drought, disease and fire. The proliferation of standing dead threes has forced firefighters to change tactics, sometimes cutting containment lines farther from the flames to avoid the danger of injury or death from falling trees.

A state-by-state look at the numbers of standing dead trees in 2015 compared with previous available totals:

Arizona: 275 million, up 4.8 million since 2010

California: 499 million, up 29.5 million since 2010

Colorado: 834 million, up 153.2 million since 2010

Idaho: 814 million, up 76 million since 2010

Montana: 1.2 billion, up 159 million since 2010

Nevada: 145 million, up 1 million since 2012

New Mexico: 341 million, up 20.4 million since 2013

Oregon: 571 million, down 7.7 million since 2010

Utah: 436 million, up 30.9 million since 2010

Washington: 593 million, up 24.3 million since 2011

Wyoming: 619 million, up 8.8 million since 2012

Source: U.S. Forest Service Forest Inventory Analysis Program

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