naturally. reporter: on land owned by the save the redwoods league, we hiked out to see just how deadly the cassel fire was here. for us to see 10% to 14% of the total of giant sequoias alive killed in one year, in one fire, there s nothing to compare that to. reporter: yet fire in and of itself is not the enemy of the giant sequoia. their cones open up. their seeds start to germinate after a fire. reporter: so near those lost giants, where the fire wasn t too intense, small shoots of hope take root. what i see is a lot of these little baby giant sequoias that have sprouted up since the fire happened. reporter: without an urgent response to the climate crisis and increased forest maintenance, experts worry more of the once seemingly impervious sequoias will be lost. the biggest worry for me is we have two fires burning right now that are threatening groves that we have not been able to
it s lived more than 3,000 years, and yet we re seeing that wildfire is threatening these giant sequoias more than ever before. the cassel fire was a wake-up call. an estimated 7,500 to 10,600 trees were destroyed in that one fire alone. reporter: started by lightning in august 2020, the cassel fire was part of the sequoia complex that burned more than 174,000 acres, scorching several sequoia groves. it was devastating, heartbreaking. everything had been incinerated. it was a field of the world s largest burned-up toothpicks. reporter: after decades of suppressing forest fire, other trees and brush have grown rampantly around the sequoias. the fires that used to burn every five to ten years in the sierra would just keep down the competition and reduce the fuel