That's weird, I tried that by placing a big black dot on all tree bmps in the foliage directory and moved them to Z, then loaded up game this is what happens. At a distance they all had black dots but as I moved the view closer, a more "high res" tree replaces them.
See the trees in the back with the black dots.
Once I move closer a higher res version is apparently used, note no dot now, so the close ones must be located someplace else.
Or am I missing something?