Contrary to the common belief that forest dryads (in my culture they are called Mavkas) sleep in their trees during winter, some may awaken in the midst of winter. They check if everything is in order in the forest, heal trees if needed, and cover them with snow.
But beware, these are not the cheerful and carefree dryads of summer that a random traveler might encounter in sunlit clearings, relying on them for help. A winter-awakened dryad is a creature of ice and cold, ruthless, especially to those who entered the forest with an axe...