I'm sprucing up many of my scenics with shrubbery, and I like the effect.
Preserved lichen can be purchased at any hobby store (I boycott Hobby Lobby) and averages around six dollars per bag. The lichen in the bag is pretty compressed so when you dump it out and leave it overnight it expands to its actual size. As you can see above, there's a lot of product in the bag. Craft lichen comes in a range of color mixes from spring to autumn foliage.
This is one of my stepped, upland scenics which looks pretty sterile.
Hot glue is the perfect adhesive for lichen which is very spongey and the hot glue gets a particularly good grip.
Lichen grows naturally in moist wooded areas. The greatest cache of lichen I've ever found was at Detour State Park in upper Michigan. Lichen in its natural state is quite stiff, and as it dries it becomes increasingly brittle and eventually breaks down. Craft lichen, however, is pickled in glycerine and remains soft and pliable though perfectly preserved.
Even just randomly sprinkling the clumps of lichen over your battlefield will really enhance its appearance. When the smoke clears, just pack it all up in a large Ziploc bag where it'll remain dust-free until the long-roll sounds again.