A squirrel is sitting in a tree...
A squirrel is sitting in a tree enjoying the sunset when all of a sudden the whole tree starts to shake and rumble. He looks down and sees an elephant climbing the tree. He yells at the elephant,
"Hey, get out of my tree, elephant! What are you doing man!?"
"Sorry squirrel, I'm just coming up to eat some pears."
"This is a pine tree. There are no pears up here!"
"Well I brought my own pears."
There is an elephant in this joke, but I don't quite know if it is an elephant joke, because they are usually short, and strung together in large series. The humor in this joke lies in the absurd nature of the conversation. The squirrel plays the part of the straight man, and the elephant is the vehicle of the joke.
Everything that the elephant does is unexpected - first he is climbing the tree (which elephants don't do), then he says that he is going to eat pears in a pine tree, then he brought his own pears (which makes no sense, since if he had his own pears, why would he have to climb a tree to eat them?)
The punch line is the end of the joke, and it it humorous, however for such a long joke it really isn't that funny, so this is almost a shaggy-dog story (where the humor lies in the length of the joke and the weakness of the punch line).
With all this said, when I read this joke for the first time I laughed quite a bit, so there must be something that I am failing to understand about the joke.