I think Wilton has a branch & leaf mold if you prefer going that route.  I would experiment using a dark brown fondant and then using white food coloring to paint over it to create the birch look. Or maybe use white and try painting with the dark.  I googled "birch camo wedding cakes" and saw quite a few that might help you decide how to create this look.  I found one on Pinterest (sorry, I can't tell where the original pic is from) that looks like what I'm trying to describe.  http://media-cache-ec0.pinimg.com/originals/da/5d/d2/da5dd2359ab4454e4a97a93858260fda.jpg

Also, I apologize for commenting totally off topic, but I'm a bit obsessed with wedding gowns and I just checked out camoformal.com.  I had no clue anything like that existed.  I am speechless, and that doesn't happen very often.