THREE RIVERS, Calif. (AP) — Sunday’s hot, dry weather added to the challenges facing California firefighters who are battling to keep flames from driving further into a grove of ancient sequoias, where the base of the world’s tallest tree has been wrapped in protective foil.

Fire officials warned that stronger winds were also contributing to “critical fire conditions” in the area of the KNP Complex, two lightning-sparked blazes that merged on the western side of Sequoia National Park in the Sierra Nevada.

The National Weather Service issued a red flag warning through Sunday, saying gusts and lower humidity could create conditions for rapid wildfire spread.

The fires forced the evacuation of the park last week, along with parts of Three Rivers, a foothill community of about 2,500 people. Crews have been bulldozing a line between the fire and the community.

More than 34 square miles of forest land have been blackened.

The National Park Service said Friday that flames had reached the westernmost tip of the Giant Forest, where it scorched a grouping of sequoias known as the “Four Guardsmen” that mark the entrance to the grove of 2,000 sequoias.

Firefighters wrapped the base of the General Sherman Tree, along with other trees in the Giant Forest, in a type of aluminum that can withstand high heat. It wasn’t immediately known how the Four Guardsmen, which received the same treatment, fared, fire spokeswoman Katy Hooper said Saturday.

The General Sherman Tree is the largest in the world by volume, at 52,508 cubic feet, according to the National Park Service. It towers 275 feet high and has a circumference of 103 feet at ground level.

Firefighters who were wrapping the base of the sequoias in foil and sweeping leaves and needles from the forest floor around the trees had to flee from the danger Friday, Hooper said. They returned Saturday when conditions improved to continue the work and start a strategic fire along Generals Highway to protect the Giant Forest grove, Hooper said.

Giant sequoias are adapted to fire, which can help them thrive by releasing seeds from their cones and creating clearings that allow young sequoias to grow. But the extraordinary intensity of fires — fueled by climate change — can overwhelm the trees.

“Once you get fire burning inside the tree, that will result in mortality,” said Jon Wallace, the operations section chief for the KNP Complex.

The fires already have burned into several groves containing trees as tall as 200 feet and 2,000 years old.

To the south, the Windy Fire grew to 28 square miles on the Tule River Indian Reservation and in Giant Sequoia National Monument, where it has burned into the Peyrone grove of sequoias and threatens others.

The fire also had reached Long Meadow Grove, where the Trail of 100 Giant Sequoias is a national monument. Fire officials haven’t yet been able to determine how much damage was done to the groves, which are in hard-to-reach areas.

Historic drought tied to climate change is making wildfires harder to fight. It has killed millions of trees in California alone. Scientists say climate change has made the West much warmer and drier in the past 30 years and will continue to make weather more extreme and wildfires more frequent and destructive.

More than 7,000 wildfires in California just this year have damaged or destroyed more than 3,000 homes and other buildings and torched well over 3,000 square miles of land, according to the California Department of Forestry and Fire Protection.