Arbor Day started here in Nebraska.  If you want some ideas of how to celebrate, visit the National Arbor Day Foundation. 

Also, there is a campaign going on called Vote Yes for Trees.  Emma, an email marketing service (noninvasive and no spam), vows to plant up to 5,000 trees for the nonprofit Trees, Water, & People.  My vote made over 1,000 trees.  The votes will be tallied now through Memorial Day.