I suggest an adjusted value taking burn into account. E.g. you use 20% or whatever of the value. Theory: it ain't 0 if you plant a tree and it is not the whole tree. There has to be a % that represents on average the effectiveness of the plant over 200 years say.
Ok. But what about just making the credits 5x more expensive without requiring monstrous bookkeeping of tree populations and their associated credits over centuries?
This also addresses the tree death issue.