I don't know that I'd categorise the nomadic hunter/gatherer lifestyle as being particularly "green". Most Aboriginal tribes, by way of example, would camp in an area and eat what grew and roamed thaere naturally, until it was exhausted, then they'd move on to the next area. Sometime later, when the area had regenerated, they'd moved back. Okay for species that can adapt to that kind of exploitation of an area, but I imagine that that lifestyle took its toll and was responsible for many extinctions, especially when you take "fire farming" into consideration. Quite simply, the idea was to burn an area of bush so as to make it easier to hunt animals, either spearing them as they escaped the fire, or providing them with less cover and making the hunt easier. Many Australian natives plants need intense heat for their seeds to germinate, so this hunting method worked out well for them. Now the "native caretaker" myth suggests that groups that practiced this were doing so in harmony with the environment, whereas the true case may be that the environment harmonised itself with the way the fire farmers did things, with flora and fauna that couldn't take the fire farming dying out, and those that could surviving and thriving. A case in point may well be the Wollomi Pine. A tree supposedly left over from the Mesozoic Era (dinosaurs, people!) it was discovered tucked away in a ravine in the Blue Mountains where it (and presumably its ancestors) had never been touched by fire, man-made or otherwise. Who knows how many other such species have become extinct since the arrival of the Aborigines and their "fire farming"?
In North America, some Native American tribes are known historically to have stampeded gigantic herds of bison over cliffs, only taking the few carcases they could possibly use, and left the rest to rot. That's hardly the "take only what you need" mythos of the hunter-gatherer society.
Agriculture, on the other hand, leaves a smaller ecological footprint. You only farm the land needed to produce stuff for you and your family, and the rest can get on with it's life. Agriculture represents true harmony with nature, because you only get anything out if you put in first. You must practice conservation by holding back seeds and animals for next year's crop and herds. You give to the land in the form of sowing, fertilising and caring for your animals and you practice further conservation by preserving and pickling the excess harvest.
I know this appears to be "Devil's Advocacy", and I probably look like I'm being contrary and difficult, but I've been considering a lot of this stuff, long and hard, for many years.
