 Trees  have been described by literary critic Guy Davenport as " the one poem known by practically everybody . " According to journalist Rick Hampson , " Trees " was " memorized and recited by generations of students ... It comforted troops in the trenches of World War I. It was set to music and set in stone , declaimed in opera houses and vaudeville theaters , intoned at ceremonies each April on Arbor Day . " According to Robert Holliday , Kilmer 's friend and editor , " Trees " speak " with authentic song to the simplest of hearts . " Holliday added that this " exquisite title poem now so universally known made his reputation more than all the rest he had written put together " and was " made for immediate widespread popularity . "