Those are called polypores. Ancient people used them to start fires. Once dry, you can cut off a chunk and lite it. It will just smolder for a long time. You wrap the smoldering chunk and carry it with you. It has just enough heat to start a fire. Otzi the ice man found in the Alps had a chunk with him. I worked in a machine shop and took a chunk to work. Lit it and tossed it under a ladies CNC machine. It smells like an electrical fire. It took the machine repairman an hour to figure it out.😎