What is the importance of the underground cavern in the book, Eden: A Novel?

The Underground Cavern is a huge series of caves under the city of Eden which were originally the backup plan in case the above ground city was not ready for occupation on time. The cave has a large camphor tree thriving in the middle of it and is fully automated, but on a system separate from Eden. There is a large central cavern where the tree grows surrounded by smaller rooms that are used for individual bedrooms. The cavern is functional for a large group of people, including running water and showers.