Tree Steam?

Here is a question for the naturalists.
A few nights ago, we had a heavy rain. The next morning, as I was walking through the park, I saw the trunk of a pine tree, struck by a shaft of direct sunlight, giving off steam.
Huh?
I went over to investigate. It was warm, perhaps from the sunlight, not hot; there was no fire.

Have I passed by thousands of pine trees giving off steam and just never noticed?