Suitable trees are installed according to design specifications and then cultured over time into intended structures. Some designs may use only living, growing wood to form the structures, while others might also incorporate inclusions [1][2] such as glass, mirror, steel and stone, any of which might be used either as either structural or aesthetic elements.[30] Inclusions can be positioned in a project as it is grown and, depending on the design, may either be removed when no longer needed for support or left in place to become fixed inclusions in the growing tissue.[3]:117