Meaning of this line from "Birches"

Question

I was reading "Birches" by Robert Frost. I am having difficulty in understanding the meaning of a line.

Please refer to this link for the full poem: https://www.poetryfoundation.org/poems/44260/birches

What is the meaning of this line:

They click upon themselves

As the breeze rises, and turn many-colored

As the stir cracks and crazes their enamel.

What does "click upon themselves" mean? Does it mean that the trees collide with other trees and exhibit a to and fro motion or does it mean that the trees hit the ground and then return back to their original position? I could not understand how "and turn many-colored/ As the stir cracks and crazes their enamel". How do they turn many colored and does "enamel" here mean the ice covering the bark of the tree or the bark of the tree itself?

Answer 1

The trees are covered in ice, and "as the breeze rises", they make clicking sounds as different ice-covered parts of the tree collide. The breeze (or "stir") cracks the "enamel" - the ice covering, and so as it falls off, the many different colours - white, green grey - are revealed.