this is a word created by george bush(also see w or john kerry-antonym on august 21, 2001... as quoted by usa today.
it refers to trees. or at least it did until arbo-tree-ist came into existence. see arbo-tree-ist.
"arbolist...look up the word. i don't know, maybe i made it up. anyway, it's an arbo-tree-ist, somebody who knows about trees."