Martin,
Do you have a lot of deer there? I just finished a forest stewardship conference last weekend. One of the subjects they broached was, if you have a fern problem, you probably don't have a fern problem, but a deer problem. Now, I realize New York fern is invasive and bad but, what usually happens, is any time something does manage to grow up through the fern, the deer eat it off do to lack of other feed.
Back to your questions: If you do not get the roots the fern will come back up. The only way to handle the problem, would be to spray and kill the fern back. Also, the Mountain laurel is also a bad thing as it puts too much shade on the forest floor for other plants to survive. I do not know about the toxicity problems. Ginseng needs shade but, it also needs sun. You might want to try small amounts to see how it will take. Wish I could offer better hope.
