A good question. Let us know if you experiment and come to a solid conclusion.
It has been a while since I have made a map, but I think that the trees are placed as already mature in the map editor. I have never noticed trees placed with the map editor to change size, so my guess is that the map editor tree tool only plants fully grown trees.

Well, it would seem that trees and bushes placed by the landscape editor are counted as mature for both tourism and for logging, while trees placed otherwise are immature and are not counted.