Over the weekend I saw some trees (and ivy) that were being removed. I'm not sure if the trees were rotten, or if they wanted to remove the ivy and the trees were collateral damage or what.
In any case, I'd never seen a tree girdled this way. I imagine that a chainsaw was used. Trees move nutrients from the ground and their leaves through and just underneath their barks -- what we think of as "wood" is like a skeleton, in a tree it mostly provides structural support. Removing a band of bark all around a tree's trunk kills it.
At first I was drawn to the contrast between the curved lines of the tree and the geometric square cuts around its trunk. But looking at this photo reminds me of a pirate skull's teeth.