I learned about cubical brown rot (a type of wood-decay fungus) in Robin Wall Kimmerer's book Gathering Moss. Brown rot fungi break down the structure of wood in such a way that it falls apart in roughly cubical pieces. I would guess that's what's going on here (Indiana Dunes S.P., April 2024).

The book (Gathering Moss, Robin Wall Kimmerer) is wonderful, and I highly recommend it. The descriptions of the mosses are beautiful, and it was interesting to learn about the field work involved in her work.

I read that early land plants couldn’t stand up until they developed lignin, and then for millions of years nothing could break it down. We were saved from infinite pile of plant debris once fungi could digest it.