I have been learning about Yellow birch and have come to understand they regenerate by dropping seeds on old rotten stumps. The tree grows and stumps rots, in some cases the rots suspend the tree off the ground with the many roots looking like legs holding up the tree.
The next time I see a good one I will get a picture of it. Here in Timmins we are at the northern edge of the range of Yellow birch.
This balsam fir tree growing on this rock looks very healthy right now. I think the rock is too big for the little guy to make it possible for the roots to reach the ground.