From the helicopter, Charlie Castro could gaze down into the heart of the tree, a hollowed-out cavity alive with raging red flame.

Just hours earlier, he had been in Montana, where forest fires were racing across the timberland. But when lightning struck one of the giant sequoias in California’s celebrated Grant Grove, sparking a blaze that threatened to spread across its thousand-year-old trees, the National Park Service needed a firefighter who could climb right up to the conifer’s burning crown, succeeding where efforts by land and air had failed.

It was a job that Castro, an Indigenous tree climber, was uniquely suited for. It would also be one of the greatest challenges of his career.

Part of the last generation born and raised in Yosemite national park, Castro – a member of the Mono Paiute and Miwuk tribes – has witnessed first-hand how fire has reshaped the American west, intensifying into the massive blazes seen today.

He has also been on the frontlines of change, watching as public understanding of wildfires has shifted – and with it, park policy.

But on that day in August 1967, Castro alone would face the flames. As he circled high above in the helicopter, Grant Grove stretched out below him, the jewel of Kings Canyon national park.

Some of the largest trees in the world towered under his feet: giant sequoias stout enough for cars to pass through their trunks. One of them, the General Grant Tree, was considered the second-biggest tree in the world, with a trunk volume of 46,608 cubic feet – nearly 50% larger than the cabin of a Boeing 747 airplane.

And in their midst burned a matchstick. Known as the California Tree, the flaming sequoia was spitting hot embers into the air, dangerously close to the General Grant.

Armed with pencil and paper, Castro started to map his plan of attack. Because tomorrow would decide whether the trees could be saved.

Tomorrow, he would start his perilous climb.

Read the rest of Charlie Castro’s story on The Guardian’s website.