I would take anything said by Piers Dudgeon with a very large pinch of salt. His first book on Barrie and the du Mauriers, Captivated was full of weird conspiracy theories, plagiarisms, misquotes, citations out of context and complete fabrications. I haven't bothered reading his book on Michael LD as I suspected it was full of the same, trying to fit events around his own theories. If he doesn't say where he saw the initials on the tree, I doubt he's actually seen them.