This sounds like some variant of coppicing being practiced, if only they hadn’t retained that much trunk.
Feet! How the hell would I notice something 8 inches high while driving by?
I’m guessing that the trees actually do have bark, and are just of a species which looks bald due to not having much cork.
Vertical elements “placed in a straight line, a few feet apart” suggest posts for a fence to me, with the panels/pickets/whatever to come later. Maybe I’m just not seeing it.
Have you seen the triptychs at Stonehenge?