Maidenhair fern, my favorite fern
We've gradually started replacing hostas—our previous choice for shady areas—with other plants. Ferns, of course, are a lovely substitute for hostas. (I had at one time been enamoured with hostas, collecting quite a few different hybrids of that Asian plant.)
They're certainly a part of our Northeast forest ecosystem, but we don't expect the usual type of habitat value from them. As Tallamy points out in The Living Landscape, even though ferns are one of the most ancient group of plants, insects haven't figured out how to exploit them. However, they do provide cover for various creatures.
Ferns emerging are a beautiful sign of spring
The bottom line is that they're greatly preferable to the usual kinds of non-native groundcovers people typically use.
(And I can't help but wonder if there are associations between ferns and the rest of the forest community that we're not even aware of yet …)
Here is a list of the ferns we grow in our habitat garden.