P.S. Can't plant a tree today? You can still buy used books! They not only save trees (as opposed to buying new), but they also smell better and cost less, and little used bookshops are the most fun to wander through.
Do you have a favorite used bookshop? How about a favorite tree--either a specific one (e.g. the ash at my parents' house that I always refer to as The Climbing Tree) or a species (mine is sugar maple)?