Comment by seadan83

Big brick is a metaphor. Not compressed, but solid. Essentially enough plant matter that you can't walk through it, plant matter that is "solid" from ground to the tree branches.

For example, on this site: http://willhiteweb.com/washington_fire_lookouts/miller_hill/...

This image: http://willhiteweb.com/washington_fire_lookouts/miller_hill/...

I've seen unburned forests where that undergrowth is more dense and taller. The more time, the more that underbrush thickens and grows. Eventually there is an old growth forest and that stuff is shaded out. AFAIK that process plays out o er centuries. We're typically in the first century of growth for west coast forests (few old growth forests remain)

Compare for example with these images of a post-burn forest: https://www.nytimes.com/2018/09/25/nyregion/nj-pine-barrens-...