How can I divide my foliage into sublevels?

I have all my foliage on one sublevel, and I want to divide it up into various other sublevels from there, how would I do that?
What I did was add foliage en masse to a static mesh of my map using the fill tool, and then dropped the foliage to the terrain, so that way I don’t have to paint it manually, and I can cover the whole map quite easily.
I just need to figure out how to divide the foliage up into sub levels now.

The mesh is essentially a foliage mask that allows me to add large amounts of foliage where ever it exists. I use multiple meshes to cover different regions of the map.