Land ownership is an arbitrary right created by the government. It's not a natural right, because natural property rights start from the idea that the fruits of your labor are yours. But because the land was already there before humans, it's not a fruit of anyone's labor. You can have natural rights over the land you are actively using, but you will eventually lose those rights if you stop using the land.
And because land ownership is a right created by the government, the government can define the terms and change them.
And the dominant entity in human societies is the state with military and police forces. If we continue with this line of thought, the state has the natural right to decide who is allowed to use which piece of land, under which terms. And it has also the natural right to change its mind.
And because land ownership is a right created by the government, the government can define the terms and change them.