Yes indeed! The princesses control the rise of the sun and the moon, pushing the world along on the calendar. The pegasi are able to move clouds into position or destroy them, bring moisture into the air to make new ones, take care of the strength and direction of the wind, and so forth. Earth ponies take care of things down below, clearing snow and readying the fields, waking up animals from hibernation and such. And us unicorns use our magic to help out in any number of ways. In fact in Canterlot, where most of the population is unicorns, the shift from winter to spring is basically just one big spell.