Some most popular and treasured trees in California are under threat as the KNP Complex wildfire spreads inside the Sequoia National Forest.

The blaze has been monitored inside the Giant Forest – home to the General Sherman Tree and Four Guardsmen. In an effort to protect the trees, firefighters on Friday covered them in aluminum wrap that can resist fire. Within the grove are more than 2, 000 ancient trees.

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

The fire was triggered by lightning last Sept. 10, which was fanned further by high winds on Friday. It grew to 21, 777 acres Sunday morning from 18, 000 acres on Saturday.

“The fire reached a small area of the Giant Forest [Friday], in the area known as the Four Guardsmen, where trees had been thoroughly prepped in recent days,” according to Saturday’s incident report of the Sequoia & Kings Canyon National Parks. “The General Sherman Tree did not see fire yesterday. Hotshot crews are assessing on the ground this morning to ascertain if conditions are stable enough for more crews to reengage in this area.”

The degree of damage was still undetermined as of Sunday afternoon.

The German Sherman Tree is an important part of California history – having lived and watched for more than a thousand years. The species is said to live at least 2, 300 years and is the largest in terms of volume even if it is not considered to be the tallest in the planet. The German Sherman Tree can grow up to 275 feet tall and more than 36 feet in diameter, the National Park Service said, as reported by SFGATE.

On Sunday, a red flag warning was released for additional gusting winds. Firefighters are clinging on to hope that their backfires close to the Giant Forest on Generals Highway can put some vegetation to blaze, and turn out to become protective shields surrounding the grove.