Gilles Clément [http://www.gillesclement.com/] installed in 2009 Aspens (poplars) to make this huge Nazi megastructure, located on an industrial port area, more ecological. Trees can still be seen on the roof of the U-Boat bunker. It's unfortunately almost impossible (if you respect the rules) to take a pictures from the Fangrost structure, but the planters can be seen by a little passage. https://submarinebaseinbordeaux.wordpress.com/