Feather trees

centuries ago, a githzerai monastic order that originated on the plane of Limbo used botany as a way to study the elements and by comparison themselves. This lead to the creation of the Feather Trees (trees that float).
The order expanded and a branch was created on the material plane. They, of course, brought the Feather Trees with them.
In more recent history a pirate lord came upon this unique resource and butchered all the monks of the order and stealing the trees. He then commissioned the best shipbuilder to create the first flying ships.
So, present day, a small island has the only known source of Feather Trees. A group of sky pirates are pillaging the world and guarding the little island with their very lives. Also, scouts were sent by the githzerai order to determine what happened to the material plane branch.
https://dungeonmasterblock.freeforums.net/thread/1642/dm-nastics-87-journey-destination