Q: Why is a tree like a noisy dog?
A: Because each has a lot of bark!

Explanation:  Dogs bark; barking is the noise they frequently make (some dogs bark less then others).  In this case, ‘bark’ is a verb, an action.

Trees have bark; when you touch the trunk of a tree you are touching the bark.  In this case, ‘bark’ is a noun, a thing.

This joke is funny because it plays with the two meanings of the word ‘bark.’

Here is a barking dog running up the trunk of a tree, touching the bark, of course.

Thanks to a student of mine for his inspiring care for dogs!