Nothing that is exposed to the elements, to the course of time, will be able to remain alien to its incidences. The plastic art arranged in walls and other similar spaces will be modified with more reason by the inclemency of the weather; sometimes favoring it. I wouldn't dare say this for the work you show us in your photo. Seeing those green spots on him, it occurred to me to think of the effect that "nature" can have, as you say, as if it were Pollock's "action painting" or "controlled chance".