I found a "Geometry Paint" plug-in for maya. It's part of the Bonus Tools autodesk made, which you have to install... which took me ages to get to work 8E.

Its basically like the paint effects tool, but for custom meshes.

http://area.autodesk.com/bonus_tools <- link to the download



I tried it out on a plane (above)(the plane is hidden).
We can use this to populate the ground folliage, and the leaves/needles on the trees.

Do you want pine trees with real leaves or with pine neeedles? I can look more into how to paint textures on the planes for this.

I also found a script, which was for leaves created by paint effects trees, that changes the UV layout of the leaves, so that you can have different textured leaves.

http://www.djx.com.au/blog/2011/03/10/maya-paintfx-leaf-uv-layout-script/ <- linky to that.