I missed this thread and was referred to it by the NA vs Europe discussion.
Chris Johnston wrote:
With all due respect, what is being discussed here is moss for exhibit, not moss growing on the surface of the soil. When a tree is shown at Kokufu Ten, the tree will (usually) be potted in an antique container just for the show, and moss will be carefully and artistically placed just for the show. As soon as the exhibition is over, the tree will be returned to its regular growing pot and the moss will most likely be removed.
Chris, having visited many bonsai gardens in Japan, including the Imperial Palace bonsai collection, and having photographed many of the trees, I can attest that many top quality Japanese trees have their soil totally covered in moss while growing in the garden. Even so I have witnessed apprentices removing the regular moss and replacing it with new moss that looks more artistic for exhibition. Moss and other ground cover is a key component of showing a tree.
I am going to post a couple of sample shots - a bunch of pines growing in a shed in the Emperor's collection. These are average run of the mill trees in Japan. They are not being exhibited any time soon. Note the moss.
A photograph of Kimura's famous Shimpaku. Not in a show (see the algae on the live vein), just living in the garden.
Finally, a pine for sale in Takamatsu. The moss is peaked but totally covering the soil.
I have hundreds of other photographs that back this up. In fact, it is the exception that doesn't have moss on all the soil.