I think those tree brushes has a lot of potential. They are too big for most maps right now, in my opinion, but if you'd use a smaller size and, as you say, a little less color variation (mapping isn't necessarily about perfect depiction of everything, after all, but about finding a representation that conveys what you want it to convey (which can of course be photorealism, just doesn't have to )), I think it could make a very interesting forest.

Thanks, Azelor