What is truly hilarious about this, however, is that someone reproduced the joke in the actual “wood” article, essentially verbatim. Of course it was marked as vandalism and posts were temporarily disabled, but it lead to a highly ironic and amusing discussion in the Talk:Wood section about what exactly the point of the joke was supposed to be.
XKCD Comic: http://xkcd.com/446/
Wood article: http://en.wikipedia.org/wiki/Wood
Talk:Wood: http://en.wikipedia.org/wiki/Talk:Wood (you have to scroll down)