One way to proceed might be to locate some area of old-growth or older-growht forest nearby you, and see what understory plants are growing there. Many of these are very slow to propagate and colonize areas of younger forest and you can jump-start the process. I would beware of doing this by transplanting directly from older forest areas except under strictest protocols for
sustainability. That said, some of these plants depend on mycorhizal fungi, some of which are also in relationship with the
roots of the trees themselves. Moving a bit of soil with the transplants might be a good way to get these beneficial relationships restarted.
There are quite a few
native understory plants (and exotics also, I'm sure) that are edible and/or
medicinal, indeed, several are so valuable they have been endangered by overharvesting (ginseng and goldenseal come first to mind). Getting these established thus can benefit both your ecosystem and you.
You may well need to exclude or deter
deer and possibly other animals from the areas where you are trying to establish these things....deer are often overpopulated relative to the primeval condition. Invasive exotics, too, may be present or may appear because of, or in spite of, your activities.....bringing in nursery-grown plants or soil from off-site is a notorious way to do this. Some exotic woodland plants are also edible, useful, and not aggressive....the edible shoots of some hostas come to mind......
Another point to remember is to observe the site carefully for several months, or preferably still an entire cycle of seasons, to be sure you know exactly what is growing there....what, where, and when. Some of the woodland ephemerals come up and bloom and die down in just a few weeks, so it's easy to miss them and then disturb them later when they are invisible; this is also true of mycorhizal
mushrooms, which may appear even more briefly. One way to pursue this along with a policy of introducing beneficial plants is to start a nursery, where the new plants are kept in pots or temporary shaded beds for a while before shifting them to their permanent positions.
