Kiln-dried lumber seems much more resistant to degradation by fungi than raw timber. An ancient spruce 2x4 on my property will last a decade out in the weather. A standing dead spruce of similar dimension breaks down much more quickly. I wonder if kiln drying slightly torrifies the
wood, making it more resistant to decomposition.
I hesitate to post this, since I can't prove it -- it was told third-hand from somebody who knew a producer -- is that mild fungicides **may** be sprayed on dimensional lumber during its processing. This is pure hearsay, for the record, and may be pure BS.
Anyway, based on my direct observations, I'm not sure mushrooms would thrive in dimensional lumber as well as in a fallen tree. My 2c.