Wonderful work, Ricko - thank you :)

I forgot to add the mould!

I think I've got the fungus set sorted out now :)

I did a blog about how to make your own bitmap fill from PF symbols here:

I've been playing with the style for the first time just now, and it would seem from what I've done that the sheer number of trees may be the problem here.

You could try deleting a few of them perhaps?

My map was starting to get a little slow, but nothing like the way you describe. It was only about half a second delay.

It is a matter of taste, of course, and maybe you think the trees need to be overlapping, but they look pretty good at much lower densities.