While there appears to be some pronounced "haloing" (due to use of clarity in processing I'm guessing) around the trees, the other pronounced contrast between layers does not seem to me to be as much of a processing artifact as it is a natural occurrence, and perhaps maybe to some extent an optical illusion.
I went out yesterday evening to look at the "layering" in the Oregon coast range visible to the west of my house and the same effect was apparent to the naked eye. That is, if you pick one of the "layers", it appears that brightness goes from light to darker as your eye travels up to the top edge of a mountain range. The top edges of mountains appear darker than below, and the bottom of the next mountain immediately above and farther away is lighter than the top of the same mountain.
It is not just that the farther away mountains are lighter in brightness, but there is also a light to dark effect going on from top to bottom on each mountain. I'm guessing this is simply due to moisture and dust settling in the atmosphere - haze thickens at lower elevations.
Nice photo!