Possible Clues:

• Tree ring shrunk a bit in salt water
• A redwood tree, especially the California redwood
• Giant California redwood
• Tree whose name contains all five vowels
• California's General Sherman, e.g
• National park including Mount Whitney
• Enormous evergreen
• Marine guards Queen, returning debt that will grow massively
• Big tree in the main including endless ring
• ''Giant'' at a California national park