No mystery there! I use the methods described in Gordon Gravett's new book on broadleaf trees 'Modelling Trees' (part 1) published by Wild Swan. I adapt some of his methods that suit me a little better. When I get a bit more proficient, (I'm not totally happy with the latest 'old' tree) I'll do a tutorial on here showing my variations in GG's methods. Basically this one is a load of twisted 22swg old iron wire, the sort that is available for gardening use and covered with a mix of tile grout, PVA glue and brown powder/poster paint, and finally finished with earthy coloured paint and green weathering powders. The 'foliage' is medium green 'Woodland Scenics' foliage mat well teased out and stuck onto the branches and then given a good coat of 'extra firm hold' cheap hairspray.

The trees around this viaduct had a nice scattering of snow to their branches this morning

Now that would be nice to model it in a winter setting. On reflection, I don't think so when I think about the hundred+ trees that would have to be made with convincing bare armatures!