Go native, that's for sure. No maples recommended? Serviceberry is great and a bonus for the birds. River birches are very nice and seem to tolerant conditions like that.

the clay is irrelevant ... see link about how to plant in clay ... which includes planting high... adding good soil to make a mound ... and NOT amending the planting hole with ANYTHING ... the base issue is drainage.. and too many peeps think adding water retaining stuff to a hole.. helps drainage.. when in fact.. it helps retain MORE water ...

to suggest that your area is devoid of trees because of clay... probably need not be said ...

the problem entirely revolves around US ... transplanting a plant IN CLAY ... and then the attendant improper aftercare ...

once you understand all that ... then you can have any tree you wish ... that is rated for your area ...

ken

Here is a link that might be useful: link

Thanks Ken. The landscaper did suggest planting the concolors high and mounding up as you stated. But he said the top of the root ball would have to be 10" - 12" above ground level (I think maybe because of the slope) and he thought that would be too much. There were very mature ash trees in this area previously, but the ash borers got them. What you say about adding amendments to the planting hole makes sense to me. But I've been getting conflicting opinions about that from several landscapers I've talked to.

Thanks Ken. The landscaper did suggest planting the concolors high and mounding up as you stated. But he said the top of the root ball would have to be 10" - 12" above ground level (I think maybe because of the slope) and he thought that would be too much. There were very mature ash trees in this area previously, but the ash borers got them. What you say about adding amendments to the planting hole makes sense to me. But I've been getting conflicting opinions about that from several landscapers I've talked to.

All my plants are in clay! I wish people wouldn't be so scared of it.

twob,
Got to give your first guy credit for having some understanding as to what he is doing and why. Those are the kind that you want to deal with, and hope you find. The others giving you info conflicting what Ken says on the amendments would be quintessential "monkey with a shovel" that I write about often. BTW there are "monkeys with a chainsaw" as well that call themselves "tree trimmers/pruners" that are as bad or worse.

As for clay, most of the time it can be managed for most plants, though there are some very picky plants I would still not touch (Franklinia for example). The fact that you have a slope actually helps as well. When I first started planting on mounds (I have clay as well) it was like planting on top of the ground I went so high. Now I typically go about half above original grade and half below. In your case it sounds as though it is a fairly significant slope, so the best way to think of it might be to plant in a whole that has no side (wall if you will) higher than 3-4". If that means the high side is 10", that OK because it will still drain due having the low side. The roots will grow out and find the level they need to be at.

Hope this helps.

Arktrees