Don't know if it is zone 4, but Cornus mas maybe. Might be a couple other Cornus species as well. Maybe a serviceberry as well.

Arktrees

Ditto to serviceberry. Magnolia stellata.

You've probably already thought of Betula nigra 'Little King' or maybe you have it I may be thinking???

Dax

There are two plants around here referred to as ironwood, Ostrya virginiana and Carpinus caroliniana. I think that Ostrya is tolerant of more dryness, but here they both grow fine on steep banks without supplemental water, so both have at least some tolerance for dryness, and we have both growing where they get more than 6 hours of sun. Both seem more tolerant of the combination of sun and dryness than serviceberry IME. I have a Cornus kousa on a west-facing steep slope, and while it hasn't grown as quickly as the one in a spot with more even moisture, it has gotten good-sized in its perhaps 10 years and blooms well. I have various magnolias that are in quite a bit of sun and get no supplemental water.

There are also some very large shrubs such as the native witch hazels, H. virginiana and H. vernalis, which seem to do fine in a range of moisture and sun conditions.

The common Eastern Redbud tree survives as understory tree but is also a very drought resistant tree that can survive full sun.

Gents, thanks for the suggestions. I actually have a ironwood, musclewood, serviceberry, redbud, pagoda dogwood, kousa dogwood and witch hazel in this area, lol. Please keep the suggestions rolling. The river birch might be a bit agressive with its roots in this area.

Cornus mas might a be good one for me to check out.

For Ken's benefit....

I have 60' lindens. I want to plant a tree under the shade of the lindens. When its time to take down one of the lindens I want this tree to adapt to the sun.

I have found that pagoda dogwood (Cornus alternifolia) prefers at least some shade or more moist conditions or a combination. IME it fails to thrive otherwise.

Would any of the larger viburnums work? IME hazelnuts aren't particularly ornamental and sucker, but are good for wildlife food. Clethra is fairly tolerant of a wide range of conditions including sun, some shade, wet and dry. Spicebush (Lindera) is a good-sized shrub and it grows here happily in full sun, but I don't know how happy it is with dry conditions since mine are in a large shrub bed and we tend to get enough rain for most things.

Bottlebrush buckeye, mountain maple, paperbark maple,

if its an understory tree why do you need one that needs full sun

I have 60' lindens. I want to plant a tree under the shade of the lindens. When its time to take down one of the lindens I want this tree to adapt to the sun.

==>> funny how facts get in the way of a great story .. lol ... knowing you well enough.. i knew there had to be a plan .... i asked for the rest of our audience .... and now.. back to the show ... see link .. lol

you might want to get rid of them now.. as it will only get trickier .. to remove a 60 foot tree.. after you plant things under it ... a real catch 22 ... you create a tree removal nightmare.. then complain that the tree service dropped large cut limbs .... and no matter how brilliant they are... stuff happens.. and i dont mean stuff ...

can you see your garden design from space yet?????

ken

Here is a link that might be useful: link

do you anticipate that once the 60 foot super competitors are removed.. that it will remain as dry in that location ...

i had a line of 40 foot sylvestrus.. may as well been the sahara under them ...

upon removal.. it is not as dry as before ...

in other words.... dont select on that variable alone ... supply the needed water in the interum ... instead of limiting yourself on that variable alone ...

ken

Waas... sounds like youre looking for long term canopy trees which usually are in a mature forest setting. Basically trees that can sit in the shade until a gap in the forest opens up, then BOOM.

Maples come to mind and so do oaks. Look up some nut trees like shagbark hickory if they are known to be hardy. Good call on the serviceberries and redbuds. You could get away with prunus nigra too. From what ive read they are quite shade tolerant. Hazelnuts should work as well. Dogwoods have been suggested and would be good fillers. You may be lucky enough to get a hardy and shade tolerant magnolia too. Some spruce and cedar species have decent tolerance up to a certain age. Beech and buckeyes should work.... CHeck out the URL below too....

Here is a link that might be useful: wiki shade tolerance list

Canadianplant makes a good point. If you KNOW you'll take down the lindens, plant something that can survive in the understory, then take off (literally) once in full sun.

There are some highway roadsides here that when the state came in to cut down all the invasives, there, in the understory, were DOZENS of healthy, although shade-stunted white oaks of 2" or so caliper that are now free to grow to their potential.

Sugar Maple and White Oak are both good for this. In fact, although Sugar Maple is only marginally native here (you really have to go about 20-40 miles to the north or west to see native trees in any real numbers), it has colonized the understory of most of the wooded areas around here. I noticed it last fall. At first I just assumed (this is normally in my car, driving down the road) that they were Norway maple. However, in fall, they're orange to red - so they're NOT Norways, the fall color is a dead giveaway. Sure enough, I went up close, and they're sugar maple, not Norway.

If nothing else changes, they will be mature Sugar Maple forests in another 100 years.