Part of "sustainability" is giving you the best protection against fire as possible. In California, many of our clients' homes and properties are in "fire zones". Considerations for garden design can go a long way in helping your home’s chances of surviving a fire. (Rebuilding after a fire is not sustainable and is a stressful process, often taking over one’s life during several grueling years to complete.)
These considerations do not detract from the primary goal of a beautiful and inspiring landscape; they are part of the invisible backbone of the garden design.