I would like to know:
Why do you add grass and flowers(the destructible for both of them) within the trees at the end of the generation?
You can barely see the grass within the trees and when you do it looks weird.
(however putting grass texture under the trees is fine)
I suggest that you have an instant fade out and fade in once the generation is done.
You can move a lot of the variable assignment to a map Initialization trigger, since configurables are generally assigned on that time frame.
The trigger Config, though mostly true to its namesake, is executed on a dialog-click, which would then initialize a lot of things, before starting up the respective triggers. That is why I would prefer moving those variable assignments to another trigger, or the statement above.
The dialog button input and the terrain generator should be separate from each other, but that does not mean I am discouraging you from using it. Rather, have the terrain generator do all the things it needs to do and just build the dialog from there.
I wanted to use this system myself for an Age of Empires sort of rip off I'm doing but there are some problems with it from a practicality standpoint. Trees and doodads block building paths making it useless for RTS matches, there are no cliffs (I feel like this would be relatively easy to add too,) the randomness of it isn't that dramatic, I've ran it a few times and the tiles don't vary much nor does the environment in general. You need water, cliffs, less saturation of trees, and the option for different environments/tilesets or greater variation within the existing tileset.