ATLANTA — Many of the nation’s largest active wildfires have been burning in the southern Appalachian Mountains, where a relentless drought has turned pine trees into torches and forced evacuations in dozens of communities.

More than 5,000 firefighters and support staff from around the nation have poured into the Southeast to try to suppress these fires, Shardul Raval, director of fire and aviation management for the southern region of the U.S. Forest Service, said Thursday.

The effort includes about 40 aircraft, including three large air tankers flying out of Chattanooga, Tenn. Tens of thousands of acres of forest have burned and about a dozen of the largest fires were uncontained, the forest service said.

High winds and temperatures and weeks without rain have combined to spark blaze after blaze in the unusually dry landscape. Numerous teams reported wind-driven fires racing up slopes and down ravines as they struggled to protect hundreds of threatened structures.

Thursday’s national drought report shows 41.6 million people in parts of 15 Southern states living in drought conditions.

With humidity so low in the normally lush Appalachians and Great Smoky Mountains, authorities are bracing for more.