There are only six Paper Trees in the whole world. You (or maybe it's just me) can only pick them once a day. I don't seem to be able to make a Paper Tree Bean (again, maybe that's just my Bean Seasoning Ineptitude).
Can Paper Trees be poisoned?
If so, it would be easy to wipe out the species (assuming the poisoner can get to the one in The Drop, which I seriously can't). And then what happens if a street needs another hundred billion notes to get created?
PS If there is a Paper Tree Bean, there should be recycled notes in the recipe.