That promptly led to hedgelaying.. (They apparently use the "cubit" to describe an elbow-to-finger measurement.)
I remember Tolkien writing about elves creating things out of living plants--like homes out of trees--and was pleased at his imagination.
It looks like he was expanding on familiar practices from the English countryside. You cut and bend stems of young trees to grow horizontally so they can be woven together to make a sturdy live fence. "The theory behind laying a hedge is easy. The practice is much harder, requiring skill and experience."
If you don't maintain them, they eventually grow into a messy line of trees.
Want to get involved? Oops, it's in the UK. Some US suggestions include: "American Hazel, Black Chokecherry, Chokeberry, and fragrant Sumac"