Left a pen of piglets a little too long in one spot -- pictures tell the tale. I'm going to switch to the electronet fencing to make the pen rotations easier.
Pigs, left in an area, will eventually remove all vegetation of all sorts; parts of it they will eat, parts they'll just root out of existance. Most of the green growth around here the pigs like to eat; and in particular they'll seek out some of the roots of the local weeds. This area wasn't planted; it's fallow this year, and not very good soil for me - lots of rocks, with a layer of clay a few inches underneath that makes drainage poor. But as a place to rotate piglets through it's fertile. One way to get use out of an otherwise low-value area.