EXPLAINER: Fighting fire with fire to protect sequoia trees

Western Wildfires

LOS ANGELES (AP) — With flames advancing toward the signature grove of ancient massive trees in Sequoia National Park, firefighters on Thursday fought fire with fire.

Using firing operations to burn out flammable vegetation and other matter before the wildfire arrives in the Giant Forest is one of several ways firefighters can use their nemesis as a tool to stop, slow or redirect fires.

The tactic comes with considerable risks if conditions change. But it is routinely used to protect communities, homes or valuable resources now under threat from fires, including the grove of about 2,000 massive sequoias, including the General Sherman Tree, the world's largest by volume.

Here's how it works:

IT'S ALL ABOUT THE FUEL

Three things influence how hot and fast a fire burns: the landscape, with fire burning faster up steep slopes; weather, with winds and dry conditions fanning flames; and fuel, the amount of material that can burn.