@Karou: I've never tried making anything out of birch bark, but I have seen the work of other artists that have and the local Anishnaabe tribes used to make canoes and other items out of that material (and I imagine some of them still do). On a few occasions, I've used plant stems/sticks in my work (for weapon shafts/handles for example), but I can't recall ever using bark, birch or otherwise. While there are probably some similarities to paper, I don't think that it would behave exactly the same.