The storm is a destructive force. Storm burns trees. Storm floods houses.
But storm can also be life force if you know right song. In Stormwright Shelf, above Maker's Perch, you can find small dirt mounds. They very fertile -- they carry inside a strong seed. All they wait for is the right song.
Once you receive the horn fly to the area west of The Maker's Perch (around [24.5, 34.0]). You will see yellow/brown dirtmounds scattered all across the area. All you have to do is use the horn near mounds to let a small tree grow. Repeat it until you have grown 8 trees and then fly back to Rainspeaker Canopy to turn in your quest.