Yavanna is a Valar in the mythology of Middle-earth, as told by Tolkien in The Silmarillion. She is espoused to Aulë, the smith, and has dominion over the living things of the world. It was she who raised the Two Trees, which gave light to the world in the First Age, before they were destroyed by Melkor and the sun and moon were created. She gave life to them by her song, and wherever she went or her voice was heard, the earth rejoiced.
Yavanna also sung of the Ents in the music of creation, and is partly responsible for their existence. They are, in a way, her stewards and overseers of the trees and plants she so dearly loved.