After getting some guidence from a model railroading friend I have assembled my first 4 trees for my layout. The armatures are made from witches broom strands, the foliage is from Woodland Scenics and the glue is Hob-e-Tac from Woodland scenics.
Yes I believe that is what they are. Around here you only see them in stores around Halloween, hence the witches broom connotation. They are mostly naturally curved with a little help from me. here is an image of what was used.
Those are excellent trees. I agree that using varying shades of scenery material will help. Some have good results with using a slightly darker color for the overall base and lighter shades to top the branches.
Joe Fugate will lightly air brush/ dust the canopy top w/ a hint of yellow. This will simulate sunlight hiting the tre tops. I will hit w/ hair spray and sprinkle on the yellow grasses.
Noch offers some very good leaf products that also can be used as a final topping material.