there was a very interesting experiment done in South Africa, by a man who had a large ranch. there were concerns that too many grazers would ruin the land, as droughts raged on. instead of reducing his herd, he increased it. he kept it on a relatively small land area, however, and this is important, he kept the cattle moving. the movement of the cattle, and their sharp hooves, pierced th dry soil, over and over again, such that when sparse rains came, the water did not run off, but was absorbed. MORE grass grew, and the more grass grew, the more water was retained, such that it began to raise the water table whereever there was a swale. eventually, seasonl ponds sprang up in these swales, which brough even more grazers, many of them wild. MORE grazers, moving restlessly (as they would if they were in constant fear from wolves or lions) brought health to the land.
here's the guy, Allan Savory: http://en.wikipedia.org/wiki/Allan_Savory
we've forgotten what it used to be like, before we came and changed the land so radically. even the wildernesses we think are so wild are not what they were 500 years ago becuase of the lack of wolves, beavers , buffaloe or cariboo, and wildfires.
ETA: the fellow has recently been countered rather roundly, so his theory might not be a good as he made it appear. . . . .