In my area most of the higher priced medicinal plants won't grow in river bottoms. Now I know your rivers up north are not quite like the rivers I am used to being in. The Ohio and Wabash river bottoms are very big areas and for the most part have water standing on them for fairly long periods of time each season. These places that water stands most usually won't produce Seng, Seal, bloodroot and a variety of other herbs. These typ plants require their feet stay dry for fairly long periods of time or are at least on well drained loamy typ soil. Our soil runs from a heavy typ clay soil to a very light almost sandy loamy soil in the hill country around the river bottoms.
As a rule of thumb, if an area retains water or ponds water to a degree after each rain, then it is not a great place to dig herbs.
As far as trees are concerned in this area. good trees would be Tulip Poplar,Ash,sassaphrass,Cherry,certain typs of Maple,Beech,and several other highland trees. Some Oak and Hickory work ok, but you don't want nothing but Oak and Hickory. A tree that most plants will not tolerate is locust. I personally don't mind a few Walnut trees mixed into the setting and some great big old persimmon trees .
