Once I have a supermarket, can I get rid of plantations?

As title says. Does the supermarket need food items produced on the island to stock its shelves?

On a related note, I still had a bunch of plantations lingering around when I got to modern era, then I converted them to hydroponics. What do you guys do with all that space? Am I the only one to have a bunch of left over plantations chilling once I get to modern era?