Lpinkmountain has given you a bunch of good suggestions, (& probably Eric also, though I didn't follow his links.) I have several additions of native trees, most of which I grow. Oxydendron arboreum would probably stay within your size requirements. Acer pensylvanicum tops out at about 35', has green and white striped bark, decorative dangling clusters of spring flowers (tho small and green) and yellow fall color and is a woodland native. Several native viburnums are small to medium, multistemmed trees: V. lantana, V. cassinoides &/or nudum (taxonomy is up in the air), V. prunifolium. all have white spring flowers in flat panicles, late summer to fall berries, and good fall color. Prunus americana, flowering plum, is a small native spring flowering tree with pink to white blooms. I don't know if it meets your requirement of long-lived, but the ones I know have been around 20+ years and are still plugging away. I didn't find any reference to how long they typically live. I don't know if you want to consider them as well, but there are some native large shrubs that include Clethra alnifolia (likes wetlands, has white to pink late summer flowers and golden fall foliage), Fothergilla major (white spring flowers and red to orange fall color), several of the native deciduous rhododendrons, rhus typhina (staghorn sumac, which suckers, but has the most gorgeous fall colors of any plant I know), Ilex verticillata (deciduous, nonprickly winter berry holly), and high bush blueberries. One additional note: I have Cornus alternifolia growing in full sun and full shade and every light level in between, and it's truly a four season tree: creamy white panicles of spring flowers, late summer berries (dark blue with bright red stems) and nice overall shape, peachy fall foliage, and great winter branch structure. It's fuller in sun than in shade, had more blooms, and is nicer foliage color.

I've got dry, sandy soil and the dominant native deciduous tree is Northern Pin Oak (Quercus ellipsoidalis). Its relatively fast growing (about 2'/year can be expected) and has nice fall color. I'd also be inclinded to try Honeylocust (Skyline would be a good choice). Again, fast growth, nice form, and good fall color. A couple of others to consider are Catalpa and Hackberry (Celtis). If its an extremely difficult site, and you're not concerned with thorns (or neighbors scorn), you might consider Black locust (Robinia). It will love these conditions, and proceed to spread its love all over. If you want this slope covered quickly, this one would do the job for you. It does have lovely fragrant flowers, but should be used as a last resort. Good luck! Bob

Greenthumbz, those are gorgeous pics! I've heard that there are a couple of trees that are not native to North America but are used by significant numbers of native insects. 1) Malus/Crabapples - native, hybrid, or exotic, Douglas Tallamy's book stated that the leaf chemistry is so similar that North american insects will use all species. This certainly bears true in my experience. I've got lots of crabs, a few specimens and a crazy wild thicket full of them in back,and they are bird magnets, not just for the fruits in the fall but for the nectar and insects in spring and summer. 2) Picea abies/Norway spruce - don't have any personal experience, but was told this by an ornithology student at Cornell who was doing a study on the subject

Some sort of dogwood - Cornus drummondii, or Cornus racemosa, maybe. Cotinus obovatus is a native smoketree, but would get too big for your spot. Redbuds generally stay compact, and Cercis canadensis is definitely a local native. Bush honeysuckle (Diervilla lonicera) is probably not big enough for what you have in mine. I am guessing that there has to be some sort of Holly or Viburnum that would do well in that type of situation as well.