I never heard it called tree town. The wayback machine page for the Wikipedia citation only says "Tree City USA", which is a thing the Arbor Foundation does for lots of towns.

So either the citation is out of step with the original page or a goofball put that in Wikipedia.

I lived there for 4 years and was aware of "tree town" but never heard anyone call it that. I know it as A2.

I think it has to do with the name 'Arbor' [1] than the town itself, which has a fair amount of trees in the older neighborhoods but isn't excessively forested.

[1]: http://www.oxforddictionaries.com/us/definition/american_eng...

Yea, Always related Ann Arbor with U of M, not trees :}