The suggestion in short:
Spirit tree clearings should be accompanied with a basic lighting effect, shader, or even night vision when first approached. This should fade slowly after the tree is first attacked. I do not think this should replace the mist effect currently in use.

Long version:
Recently, I was flying around in creative to find the new spirit tree and check out some new details of Betweenlands 3.4.0 (which is really neat, by the way). To make things faster I drank some vanilla potions of night vision and swiftness. It actually didn't take me long to find a spirit tree clearing, which was amazing.
I looked around for a bit and eventually decided to punch the main face. It cracked slightly and as luck would have it, at that very moment my night vision faded off. It was really cool because it was as if the entire clearing felt the blow to the tree and darkened in response.
For several minutes I actually thought this was intentional and caused by the tree. I was reminded of Avatar's Tree of Voices.

Something else I didn't initially realize was that part of the interesting atmosphere around the spirit tree's clearing was because the whole area was dramatically white, pure, and clean, unlike most of the Betweenlands. This was partly because of the night vision effect I was under. When it faded, it was as if my attack had soiled or damaged the purity of the atmosphere, turning it hostile.
My point is that I was amazed by the effect and I think adding it to the game would contribute greatly to the (already impressive) ambiance of the spirit tree and its clearing.