Goats are effective at clearing invasive species for several reasons. They love to graze, it's pretty much all they do. As they are nimble on their cloven hooves--the two halves of the hooves work independently of each other, according to Google, which helps them on uneven terrain. They seem to have no trouble getting in and around vines without getting tangled or stumbling over rocks. They can stand up against a tree to clear the vines that have been smothering it as well as weaving through ground vines. And all the while, they are chewing. 

They stop and lie down periodically to ruminate, explained Jennifer, the goatherd. (More to come on Jennifer and the other herders, including Fred Rogers, the border collie/poodle mix who is an able assistant.) While the goats ruminate, their digestive system goes to work and destroys any possibility of seeds passing through them and reseeding the same invasive plants they are ingesting. Quite monk-like...we, too, are grazing continually on everything our senses take in. And we ruminate, too. The trick for us is to choose our ruminations wisely so that we don't reseed the negativity that thrives in our world like an invasive species.