Jeff,
What materials are you considering using?
Some of the best looking deciduous tree-looking foliage, IMO, can be made with sea foam (sea moss) and Noch paper leaves. Both materials are commercially available, although I had to order mine since none of the LHS in my area carry them.
The sea foam is already dried and is pretty tough. I think it looks best if it's painted a light-medium gray (look at real hardwood tree bark). I then mist the "branch" with aerosol spray glue and dip it into a cup with the Noch leaves.
Beard Lichen (Usnea) sold by Armor Farm makes for very nice alternative armature for small trees and bushes instead of the sea foam moss. (I also like to flock it with light green ground foam for camel thorn bushes, but that's another story...)
The Noch paper leaves look better if you mix the colors rather than use a single color.
Here's an example on my Canadian Firefly:
You can make the branches as large or as small as you want to fit the contours of your tank and create the overall look you're after.
In so far as other materials, the commercially available Reindeer Moss is already preserved and colored when you buy it. Ground foam materials and foliage flocking mats made with polyester fibers and ground foam (like Woodland Scenics Foliage Mats) don't require any preservation efforts.
However, if you live in an area where Reindeer or Beard Lichens grow naturally (Eastern Seaboard and West Coast of the US), you can collect the mosses and preserve them yourself using a solution of 3 parts denatured alcohol and 1 part glycerin (you can buy both at Walmart). Soak the lichen for 3-4 hours and then spread it out on paper towels / newspaper to dry over night. Store the preserved lichen in a something like a Tupperware plastic box so that it's not crushed.
Anyways, if you let us know the specific materials you're considering, maybe someone here will have some more tips for you.
Happy modeling,
