Hi, ** **thundering1 is right, , no need to do a boolean operation, unless of course you don't want the back of the mountain, but  if you make the cubes/shapes invisible instead of deleting them you can re-populate if you don't like the look of way the trees have fell, maybe not so important when it's all covered.

And just to expand on the idea, you can have the cubes/shapes to the rear and at the sides of the camera just outside the cameras PoV, but make it so you have a slight space betwen the edges so shadows are still cast from the vegetation into view.

See the attachment,: green = ground; grey = mountains; red=cubes/shapes.

Cheers
Chris.