Not sure if this will help, I only work in photoshop, not sure if this is? But here goes.
Maybe try a HUE/SATUATION overlay and take out some color, especially in the trees.
Then maybe try a 10-20% black layer over everything, then erase areas with a 50% transparent eraser (play with these percentages)
starting from any light source. and fade out.
I would probably make the areas under the trees only slightly different color than the darker surrounding areas.
In a dungeon, your not going to get a lot of value differences - higher contrast, fewer grey values.
Hope this helps some?