Hi, thanks for the link! This is indeed a great post. I've only read this one, but I'm going to check the rest of the blog as well.
Can't help making a couple of notes :)
- No actual forestry rings are mentioned. That green circle on the diagram is just an illustration of the idea that forests would be situated farther from a city than gardens and closer than crop fields. Even on a "featureless plain" forests wouldn't be planted as rings because of roads.
- The author describes pre-modern cities, but in some aspects ancient and medieval cities differ enough to deserve separate treatment. In spite of the amount of maps from Civitates Orbis Terrarum (late XVI c) the author seems more interested in ancient history and some of the his concepts are harder to apply to middle ages. It's not related to forestry rings :)
Cheers!