Origin: Spirits of the Past , originally released in Japan as Gin-iro no kami no Agito (銀色の髪のアギト) ~lit. Silver-Haired Agito, is a 2006 Japanese animated science fiction film directed by Keiichi Sugiyama and produced by Gonzo.

Summary:
Genetic engineering on trees were conducted at a research facility on the Moon to produce trees capable of growing in harsh, arid conditions. The trees gain consciousness, wiping out Earth's civilizations and destroying the Moon. Three hundred years later, Japan is a dystopia covered by the Forest, a huge expanse of living trees, and ruled by the tree-like Zruids, which inhabit the planet and control the water supply of both trees and humans.

Agito, a young boy, and his father Agashi, as well as his friends Cain and Minka, live in Neutral City, a city carved out of the ruined skyscrapers which acts as both a buffer and a bridge between the Forest and the militaristic nation of Ragna. While the people of Neutral City co-exist peacefully with the trees of the forest, the nation of Ragna aims to destroy the Forest to restore the Earth.

One day, Agito and Cain race each other to see who can get to the water hole at the bottom of the city first. By disturbing the sanctity of the water hole and angering the Zruids, the two boys are separated. After stumbling upon a large machine with cryogenic pods, Agito accidentally revives Toola, a young girl who has been asleep for the past 300 years, and brings her to Neutral City.

Source:Wikipedia