The study of tree and shrub barks, buds, and fruits are each studies of their own. (See my book list for some reference material.) Botanists and nature lovers have hours of entertainment in the indoor study of these plant parts and the outdoor observation of the variety of tree barks, shrub buds and branch arrangements, remaining red fruits, differentiation of the evergreens... along with winter identification of herbaceous plants and shelf mushrooms.
Just the other day I saw a magnificent display of Turkey Tails (a valued medicinal polypore) - even in the cold they put of a fresh aroma. It is not uncommon to see Artist Conks, Tinder Polypores, Mossy Maple Polypores, and others of the persistent type. Old remains of Reishi and other annuals can also be found, which let us know where to look come summer.
Some important medicinal tree barks:
Larch / Tamarack
Some medicinal Polypores: