Add willows to the game.
Allow the characters to peel bark of willows, then allow willow bark (possibly after scraping, or using in-game Cooking to boil it to usable form?) be used as anesthetic herb for treating wounds.
More so for long term/serious injuries cause skill penalty, allow the painkiller to reduce some of the penalty for few hours.
And willows should only produce slender trunks when felled. Eastern and Western. I don't recall seeing any in the north (aspens and alders, lot of dwarf birches). But then, I've not been to Finnish north since 1997.. (am I getting/being old soon? )
Yes it would be nice to have willows.
EDIT: They have so many uses, tanning, plaiting, cordage (net of Antrea 8000BC was made of willow bast in Finland) etc etc.
FYI
@JP_Finn: Willow bark is almost exclusively used in tanning here up north, both traditionally and today.
Willow bark has the highest tannin content of Finnish tree barks. I read spruce has even higher, but it's messier. Wouldn't produce even slender trunks though here, with the exception of goat willow (EDIT: and few other willow species).
Willow bark is easily stripped in June. It is boiled into solution in which leather is tanned through various stages. Solution strength increasing between stages, etc. Fur-bearing hides are scrubbed on the flesh side with a 'sponge' of willow bark, wet with the solution. The 'sponge' is just bark that is scraped off with a knife in autumn, when the bark is tightly bound. That way the bark obtained is finer and absorbs more solution for scrubbing. The bark solution is boiled the same way otherwise.