GRS,
I agree with Latt.
I would not do anything to the trillium, but would just plant seng an in and around it or just plant the seng in beds and let the trillium grow right in amoungst your seng.
It is good to have other plants growing in with your seng - the diversity helps with possible disease issues.
That place with all of the trillium present sure sounds like a good potential site the way you described it.
While trillium is on the list of companion plants for seng, there is a select group of companion plants that are best to look for to determine if the site is even more ideal.
They are called cal-cicoles (normally growing in calcareous soils - rich in calcium).
From Scott's book that shorter list includes.
Maidenhair fern
Yellow ladys slipper
Baneberry,
Blue cohosh
Based on studies it has been shown that ginseng does best in soil that is high in calcium (2000 pounds per acre or more) with levels in the 3000-5000 range being even better.
Also needs a PH around 5.5.
You mentioned also finding fern in the area...
Below is a pic of some Maidenhair fern.
I noticed it growing up on a bluff hill and worked my way up there and then found that just above it, were two nice old seng plants (can see them in the pic).
Best of Luck to you on growing upper NY Seng.
TNhunter