I find that most of the player stack parts are made of yellow poplar.
You can tell by the telltale green shade of some of the wood.  Often
there will be one board that is half yellow and half green with a
definite line between them.  That is the way the wood grows.

The woods found in the stacks are not exactly like new wood might be,
as it has hardened over time.  It has also become more porous by drying
out.

I have also found a 1929 Steinway Duo-Art that had a stack all made out
of pine.  I know there were other woods used but I can't remember any
more right now.  I am sure someone will remind me in answering your
question.

D. L. Bullock    Piano World    St. Louis