How Can We Know If Livestock Benefit or Harm Our Trees?

[Scott O'Bar]

I was watching this conference with Ian Mitchell Innes: http://www.youtube.com/watch?v=27fUjjlwm7U

At about the 1 hour 6 minute mark he shows an image of a (mesquite?) tree in southern Texas and mentions how the high-density rotational grazing ended up contributing to the decline of the tree by changing the soil from a fungal dominated soil to a bacteria-dominated soil.

What do you think of that? Isn't it a concern for all silvopasture practitioners? Ian did not go into much detail and did not sound very scientific, but I've watched other presentations from him, where he presents anecdotal evidence, and it seems to be a common theme that his grazing methods will cause grass to dominate the landscape at the expense of other types of vegetation, and it all has to do with Fungal/Bacteria ratio of the soil, which is tilted more and more towards Bacterial dominance the longer one does management intensive grazing.

Anyone know of any hard science to shed more light on this matter? How are planted silvopasture trees any different in this regard than the Mesquite shown in Ian's example?