If you're referring to the llama and other S. American camelids, my understanding is that much of the high altitude native grasslands that those camelids graze is cold and sometimes even dry, not entirely tropical, and the native habitat ranges are apparently much more limited than those of the aurochs and the domestic cattle that descended from them, and the bison, deer, antelope, water buffalo, horse, and other large grazing animals. Intensive grazing could help in areas that are well adapted to grazing by camelids or other large animals. I was referring to those tropical areas that have no history of indigenous grazing animals. Savory did specify at the beginning that his lecture was not going to be about the 1/3 of the world that gets substantial year-round precipitation, so it's understandable that he didn't discuss much how monocrop agriculture caused devastating effects in areas where there were not a lot of indigenous large grass-grazing cattle, such as with the Aztec and Mayan Empires. Lierre Keith does cover the subject in The Vegetarian Myth, so if you combine Savory's work with Keith's you do get a fuller picture.
