Shaping plants.

Growing up in Lincolnshire, one of my favourite places near my parents house was Yew Tree Drive. An avenue of huge old yews clipped into shapes like a set of giant chess pieces along what must have once been the drive to a stately home, but now surrounded by woodland.

Topiary can be used to create magical spaces:

Marqueyssac, France

Other ways of training trees include cloud pruning or Niwaki:

Top to bottom: 

Japanese cloud pruned pine tree 

Niwaki in Parc Floral de la Source, Orleans, France

Unknown

Plants can be grafted and trained into weird and wonderful shapes, shown here in the tree sculpting methods pioneered in the '40s by Axel Erlandson at his 'Tree Circus' roadside attraction in California:

Similar techniques have been used here to sculpt a living chair:

www.pooktre.com