Fleur told everyone at her table during dinner at the Yule Ball that the Christmas decorations at Beauxbatons included wood nymphs, who sing to the students as they eat (GF23).
Dryads, a kind of nymph (nature spirits originating from Greek mythology), are tree spirits. Some say these nature guardians live in trees, others say they are the trees, and transform into the forms of fair maidens.
What are nature spirits? Are they beasts? Beings? Ghost? Who can say.