Technically, in a forest a fully mature stand is referred to as having a ‘closed canopy’: the tree has grown together and there is no open sky.  If viewed from above the two big oaks and the cucumber magnolia have a closed canopy.  You won’t see the north lawn in the summer from above no matter what you do.  However, trees like their space, they compete, they quarrel, and they do not happily share.  You can see the dividing line quite nicely in this photo, looking straight up: the magnolia is the left side, the oak the right (the third oak has a bit of the top left as well)