Trees

Trees were common during Rythulia's early history. They're implied to have been wiped out as Ancient Rythulians expanded their cities, and there are no signs of wood in the game. They're one of the few things that are implied not to be made of cloth.

Development
Journey was originally set in a forest. The trees were removed when the game was changed to a 3D view, because they would get in the way of the camera.

Speculation
The number of trees that used to exist could be a reference to the fact that Journey was originally set in a forest.