Before we think about the gains of the challenge, we might first come up with a way to conquer it. I agree with Matthi: Transporting a tree is something you can only master after knowing exactly how the tree will handle on the designated landscape part. Will it fall into this shaft? Will it get through this passage? Is it possible to push it up onto that cliff? If you know beforehand, you can terraform the landscape accordingly. Or plan ahead and actually construct the sawmill at the lowest possible point in the map.
Conquering the challenge would mean to have any tool ready to lift a tree. Trees fall down only and at a certain point it's impossible to bring it back up again without heavy terraforming. That's really the only tool we have (and the hardest one to master). You can't use an elevator and the rope (my personal hope of solving this problem) did not get finished. You're stuck then: trees fall down and you can't get them up again.
In ending screenshots, it's quite a common sight to have lost trees somewhere at the bottom of the map. And in CR, rescuing trees was easier (using a wagon e.g.).