Can't have it both ways BB.Should there or should there not be shade tolerant trees growing in the understory?You already admitted there should be.Do you want me to show you some examples of not only seedlings making it past the ferns?

I can show you many areas that have a mid level understory that's now over my head.The mid level understory in most places was limited by the deer eating it.Lack of light isalso a factor but like you quoted earlier,there are trees such as maple that do fine under a mature canopy.

Let me quote was you posted earlier."MAPLE IS ALSO MUCH MORE SHADE TOLERANT THAN OAK AND WILL SPROUT AND GROW UNDER A MATURE CANOPY."Nuff said.