two trees & a woodpecker

It is hard to find a joke without a dirty word or two in it, but, here is one:

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. 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. He 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 put my pecker in.'