two trees and a woodpecker

It is hard to find a joke today without a dirty word or two in it, but here is one: (An oldie)
Two tall trees, a birch and a beech, are growing in the woods. A small tree begins to grow between them, and the beech says to the birch, 'Is that a son of a beech or a son of a birch?' The birch says he cannot tell, but just then a woodpecker lands on the sapling.
The birch says, 'Woodpecker, you are a tree expert. Can you tell if that is a son of a beech or a son of a birch?'
The woodpecker takes a taste of the small tree and replies, 'It is neither a son of a beech nor a son of a birch. It is, however, the best piece of ash I have ever poked my pecker into.