moss on a tree-trunk on the tow path

Moss is a marvellous thing. There's a lot of it, on my roof, where it regularly falls off, and scatters across bits of the garden, souring the herb pots and clogging the drainage. I retrieve it and put it into places - mostly around the base of the water-butt - where nothing much else will grow so I'm cultivating a moss garden. At the moment it's based on chunks of concrete I had left over from clearing the garden. It could do with some need some big old lumps of wood for it, though. This is  a cut tree on the tow-path. It's even moister down there:





That's willow tree, grey and textured bark. I think I need to go on a bark hunt.