Tim Knowles' Tree Drawing series utilized the element of chance throughout. The technique, here, was to tie a pen to a tree branch, and place a pad of paper in front of that branch. The wind would shake that branch and result in a sketch executed by the tree. The results were actually quite nice.
The wind that drove the branch which drove the pen was random and mostly uninfluenced by the artist. In this case, the artist is the tree. At first I wondered if these pieces, although pretty, could be called art. Art is an artifact. It's something that's created. This series to me seems more like a happening than a creation, but maybe that's a misguided and malformed opinion?