Redwoods are gigantic super-efficient light sucking machines

I went to Big Basin today, which contains a lot of redwoods.

I cut short my trip a little early, convinced that my meter was consistently two or three stops under what it should be, and thus broken, and thus systematically fucked up four rolls of film. The meter is fine, which means somehow those trees were killing three quarters of the light even when the sun looked like it had broken through the tree cover and was illuminating something intensely. In the denser regions of the forest, the trees collectively killed 98.4% of the light from the sun, and the only reason any existed at all was light scatter from the blue sky going straight down.

And yet somehow there were all these low echelon green growing things that were getting about as much light as I was, which is to say 1.6% of the sun, and thriving on it. There was no grass, I noticed. Apparently grass has been bred out of existence here. Only shrubs, and trees, and I think the shrubs have tree aspirations.

How do new redwoods come to grow?