I almost mentioned that earlier... but then I decided I really like the drawing as it is.
But, I do agree. The mid-tones are missing, so there's little solidity, and that affects the appearance of recession.
So - with the understanding that I LIKE the drawing as it is - I think the over-exposed reference photo is at fault. When that's corrected (well, my version of "corrected")...
Now there's recession. The left-hand tree stands forward of the Elk; The Elk is dominant; and the trees and foliage degrade and lighten with distance. And I like the way those three left-hand trees lead my eye into the scene and directly to the Elk - and that nothing on the right-hand side is a distraction in any way - yet I can explore if I want to.