What are most dried shiitake mushrooms planted in?!

Wild Shiitake mushrooms are grow on old or decayed tree stumps or wood logs, the manufactured ones we get now, both dried and fresh are grown on prepared wood logs, they drill holes and add the inject the spores and a bit of sawdust, the mushrooms grow in clumps on the logs, they stack or layer them in moist forested fields in the woods and allow the mushrooms to form, even now in Japan they do this for Maitake, Golden Ear and Shinchu mushrooms, some mushrooms like Morels, Chanterelles and Matsutake are not grown in farmed areas, they are wild and forest made.