With flames advancing toward the signature grove of ancient, massive trees in Sequoia National Park, firefighters Thursday fought fire with fire.

Using firing operations to burn out flammable vegetation and other matter before the wildfire was expected to arrive 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 like the grove of about 2,000 massive sequoias, including the world's largest tree — the General Sherman.

The rate at which wildfires burn depends on three factors — landscape, weather and fuel. While it's impossible to control landscape and weather, firefighters can eliminate fuel — dead trees, fallen logs and overgrown bushes — by setting controlled burns to thin out forests.

The Associated Press reports that prescribed burns have been used for centuries to eliminate wildfire fuels. But in the early 20th century, aggressive firefighting and new policies from the U.S. Forest Service have led to more wildfire fuels accumulating in forests.

The controlled burns must be set with the right conditions in place and with enough time to complete the burnout ahead of the larger wildfire.

"You need to know how to fight fire before you light fire," Paul Broyles, a former chief of fire operations for the National Park Service, told the AP.

Firefighters used such tactics Thursday in the hopes of protecting the Giant Forest — setting small, tree-to-tree fires to burn up fuels in the hopes of keeping the large trees safe.

Several wildfires are currently burning in the area of Sequoia National Park north of Bakersfield. Among them are the KNP Complex Fire, the Windy Fire and the Walker Fire.