Arte Povera was an Italian movement which only lasted five years (67-72) and it was a reaction against American Minimalism and Pop Art. These artists wanted to get away from the galleries and commercial art. They didn't use expensive materials, but ordinary ones such as nature and industrial materials. Hence the name of the movement (Povera means poor, referring to the use of cheap materials).
Above you see Penone's 12m high tree. There wasn't space enough at Tate so they had to divide the sculpture in two. Penone took a wood stock and started to scrape it and by following its patterns and rings he made it look like a tree with branches again.