Well I grew up in the redwoods up in Humboldt, it is generally far to wet up there for a forest fire even occur, and if they do it doesn't spread much.

I think flooding is a far more realistic, as that happens every winter.

It has gotten much warmer and sunnier in recent years because of climate change, so perhaps forest fires will start to be a thing.

Also they don't even drop seeds until they are like 200 years old-- with all the logging that has been done most redwoods aren't growing from seeds these days, but from cuttings & off of existing stumps/roots.