I think the tree is an element of regeneration which in itself is a concept of time.

Then the tail flipped over and I was completely buried in the snow. I can see such a use for the future. The Dia Art Foundation held exhibitions of Beuys's work in 1987 1992 and 1998 and has planted trees and basalt columns in New York City as part of his 7000 Eichen a project he began in 1982 for Documenta 7 in Kassel Germany.

Joseph Beuys (German pronunciation: [ˈjoːzɛf ˈbɔʏs]; May 12 1921 – January 23 1986) was a German Fluxus Happening and performance artist as well as a sculptor installation artist graphic artist art theorist and pedagogue of art. His extensive work is grounded in concepts of humanism social philosophy and anthroposophy; it culminates in his "extended definition of art" and the idea of social sculpture as a gesamtkunstwerk for which he claimed a creative participatory role in shaping society and politics.