Uhhh... I don't know how well grass and trees would do on Mars, either. I mean, I'd like to think they'd thrive, all Dune-style, but to be honest, the environment there is slightly more hostile than ours in pretty much every way.
Also, without an ozone layer, grass and trees and stuff get sunburned too. In fact, with a little more ozone layer, they wouldn't get enough UV light to run photosynthesis. At least, that's what I've been led to believe.
-kv