I found this last year by the NYU, finally getting around to posting about it… The Treemendous Project: Mending the city one tree at a time. It was placed on the stump that the Hurricane Sandy took down. I guess there are more throughout the city and 15 artists are participating. Oh, how interesting and great! Their website has more information and a map of where you can find one.

Dear Hurricane Sandy,
We understand you were mad, so you flooded our city and knocked down a lot of homes, taking a few trees along with you.   Well, actually a lot of trees.
So, a bunch of us decided to fix that. We’ve installed artworks at those broken or barren sites in memory of the life that used to be.
As they say: “If a tree falls…”
We’re saying that we heard it, and we’re doing something about it.

I want to go find them all now.