Playing around with the settings.
I have been playing around with the styles and brushes. The dark stroke suits the maps I have been making lately but a lighter and softer stoke may suit other styles. But I really have had that much time to get this right yet.
The brush used in 'h' & 'i' is too big at 60px . So trees on each layer will need to be a similar size.
I like the feel of 'a' and 'b' myself. And i like j1 and j4. Personally I like the stroke to define the individual trees.
Trees in Photoshop using layer styles; Experiment 3
I am pretty pleased with the results of my experiments and I have just about settled on this style. I imagine that thise technique would work on town maps or small regions and battlemaps, where individual trees are decernable. For those interested I will post a tutorial in the appropriate section, in the next week or so.