What ever sells well is what is stocked at most lumber yards.

I'm sure the principles of supply and demand play a part--regular
economics. But why is there more of a demand for Cherry, Walnut and
Oak, than say Willow, Elm and Sycamore? I've never actually seen
lumber from a Willow, Elm or Sycamore or worked with this stuff.
Are these types of trees inferior for typical woodworking type
activities? Too hard to work? Ugly? They're not cultivated like
the types other types of "common" woods? They're too hard/expensive
to cultivate? There's just not enough of them? Disease (e.g.,
Dutch Elm Disease) has made them too scarce/expensive to turn into
lumber?

I think you hit the nail on the head about Elm. Having done a lot of tree
work over the years I can tell you that willow is very brittle wood, so
that's not desirable for any project I can think of. Sycamore likes wet feet
and is seldom or never found too far from a pond, lake or river. So,
sycamore is probably never found in large stands (sustainable harvest and
all that stuff). My buddy with whom I used to do most of that tree work is
now a suburban logger, picking up the logs cut by the residential tree
companies who used to be his direct competition. He has learned a lot about
sorting and grading logs for the mills. I'll ask him about the mills' demand
for specialty woods. It's really a question of knowing the right mill for
the log(s).

I do know that the best logs are not saw logs going to saw mills. The best
money is paid for veneer grade logs, which probably explains your reference
to fine plywoods.

Speaking of sustainable harvest, he bought a couple dozen acres in upstate
NY and paid for the whole dang thing with one conservative harvest of
cherry. He says he'll get a harvest like that every ten years or so as the
other trees mature.

-Dean
ready to kill a couple more Norway Maples. He said it isn't very stable and
checks a lot. I might save some for the mill anyway, just for fun and
curiosity.