First I made these trunks. I sort of did several steps at once, so let me summaries. I cut out small circles of matte board, put a small nail through the center, then used some caulk and stuck it to a small tube. The tubes were just some simple hard plastic pieces of tubing that I cut to length. Sticking out the top is a wood screw which is intended to hold the moss ball. Once all these dried I was able to move on to the next step...
To simulate the bark, I grabbed some bandage tape from the first aid kit and just wrapped it around the tube.
Next I added the moss balls to it. Pictured here are the moss balls that inspired the whole thing. They are roughly 2" in diameter and are light but relatively solid.
After that I glued some garden sand to the base and was all set to paint. The base was relatively straight forward; just base with a dark brown and drybrush a tan on top of that. For the bark, I drybrushed a medium brown onto the bandage. This gave a somewhat decent looking bark effect for the trunk of the tree. After all of the paint dried I put some random flocking onto the base and called it done.
And there it is! A completed tree! Another simple piece of terrain to upscale my battlefields.