In book one of Snyder's unforgettable Green-sky trilogy, thirteen year-old Raamo is chosen to be one of the elite Ol-zhaan priests. The Kindar people live in cities within giant trees and live off the products of the magical Wissenvine. "The Vine" provides fruits, building materials, and the roots ("The Root") cover the mysterious forest floor so that the evil Pash-shan are imprisioned below.
As Raamo progresses in his training, he learns the history of the Kindar people, how they came from another planet ravaged by war and the first Ol-zhaan were determined to eradicate these emotions from subsequent generations. Now the Kindar know nothing of violence, war, or any original thought for that matter. The people chant proscribed chants of peace and live a very restricted existence where they are not allowed to even look at the forest floor. Raamo is befriended by Neric, another young Ol-zhaan healer, who urges him to re-think everything they have been told about life in Green-sky and the supposedly evil Pash-shan monsters.
Neric and Raamo take a dangerous trip to the forest floor, where they find eight-year-old Teera lost in the forest. Assuming she is a child who has fallen from the trees, they take her back to Green-sky and leave her in the care of Raamo's family. When they learn that little Teera is not a Kindar, but a Pash-shan, or Erdling as they call themselves, their world is turned upside down.
Excellent fantasy for any age. The Kindar and Erdlings are a little reminiscent of the Morlocks and Eloi in The Time Machine. Another fantastic book that has a very similar story is THE GIVER by Lois Lowry.