Mirisalon Tree

On the elven colonized forest world of Mirisalon there are natural trees which reach 15 miles in height. Where the trees form their magnificent, large leaves, the air is fresh and incredibly easy to breathe. These trees, when removed intact from their home, maintain the ability to produce atmosphere for up to 25 years, without any mystical assistance. When fortified with the right spell engines, and regular exposure to sunlight, this ability is maintained infinitely.
Worlds capable of growing the Mirisalon Tree are incredibly prized by the Elves; they have been known to give much to steward such worlds.