Joseph Beuys Quote
I think the tree is an element of regeneration which in itself is a concept of time. The oak is especially so because it is a slowly growing tree with a kind of really solid heartwood. It has always been a form of sculpture, a symbol for this planet.
Joseph Beuys (1982), cited in: Claudia Mesch (2013) Art and Politics: A Small History of Art for Social Change Since 1945. p. 160