"Gee guys, I can't see the forest for all these damn trees".
Thanks
@William N. Valavanis for the definition. I think this thread is getting into the weeds over minute distinctions in definitions.
I won't claim any skill at creating forests. I have 6 eastern hemlock in a pot, that are too evenly spaced, just waiting for me to get around to re-arranging them. I have Dawn Redwood forest, that I took out of its tray, and broke into 2 clumps, with the intention of re-assembling them sometime in the near future. But I have dabbled. Those that have been rather dogmatic about how detailed a forest must be, I say "relax, there is such a thing as a useful approximation". In general, to make a pleasing image, a forest does NOT have to be as detailed as an individual tree. The group of trees will take the focus away from individual details of the component trees. You CAN get away with less than perfect branch placing, less than perfect taper, less than perfect arrangement. Of course we should all try our best at everything we do, but honestly, you can get away with a few lapses in a forest planting that you might not tolerate in an individual bonsai.
I like to encourage new to the hobby beginners to go ahead and try a forest, because it can be pleasing to the eye even though it is full of flaws.
More than one it has been said that a forest should all be the same species, and same cultivar if possible of a species. Those who said this obviously never visited the Ashville, North Carolina Arboretum. The collection there, curated by Arthur Joura includes a half dozen mixed species forests. These forests are world class, good enough for any public display or to be in a National level show. So to the requirement to use only a single species, I call bullshit.
It is more difficult to mix species of trees in a forest planting, because of different growth rates, and differences in apparent scale of leaves. BUT IT CAN BE DONE, and IT CAN BE DONE WELL.
The following photos were taken from Wayne S's blog, Bonsai Bark, the blog of Stone Lantern. These are from a 2014 blog, and if you search the original credit is given to the photographer.
First 2 are a forest and a close up of same forest, rhododendron & it think juniper or maybe hinoki mixed. This I believe was created by Arthur Joura,
close up
Next are 3 more mixed species forests, not sure if they are all created by Arthur or just being maintained by Arthur.
Final photo is of a forest created by Saburo Kato, one of the great bonsai artists of Japan. Again, a forest of mixed species. So please, don't say mixing species can't or shouldn't be done. Yes, it is an added level of difficulty, but it certainly can be done and can be done well.