The best way to prevent the kind of forest fires that kill trees is to allow frequent fires that clear out the underbrush and leaf litter while there's not enough of it to make a fire big enough to kill trees. That's how nature took care of it before humans started intervening. It's the human intervention that has caused underbrush and leaf litter to build up to an amount that would cause the kinds of massively destructive fires we see today. Old growth trees survived a long, long time because nature was doing a good job on its own.