Well, if we take a look at what happened with Chernobyl, it gives a pretty good indication.
http://acidcow.com/pics/16330-...
I think the plants might be that which survived it best. Plants are often used now for "phytoremediation" - for instance, some trees and grasses have been planted at Superfund sites in the U.S. because they absorb and deactivate a number of toxins. I don't know if or how plants deal with radioactivity, however.
