This is hair ice. It is formed on dead barkless wood and a fungus called Exidiopsis effusa is the main reason. I found this and many more, during late autumn in a forest in Northern Denmark
Thank you for posting this! I saw several examples of this during the recent freezing weather in the UK, and was confused as to what it was. I don’t recall having seen it before, but then I haven’t lived in a wooded valley during prolonged double-digit negative temperatures before either.