I use scouring pads to make hedgerows and conifers. I broke down and bought a bag of clump foliage as well, and I use the scouring pads as bases for canopy forests, just cut the pads to shape and coat with Aileen's glue, and press on the clumps. I mount it on a piece of box cardboard cut smaller that the scouring pad, and this give the woods the right height for 3mm. I have used lichen and flock for 6mm, but this is much easier and a bag of clump foliage from Woodland Scenics, on Amazon, is a lifetime supply for 3mm and has a great look.
I also use the clump foliage and wire to make individual trees, based in a bit of Paper Clay. Bruce