[logfromblammo]

In general, it's the current-time value of perpetual production in a particular use, multiplied by the likelihood the land would be put to that use in the future.

So if International Paper owns a square mile currently used for fast-growing trees, the value of the land is the value of the next lumber harvest, discounted over the amount of time left until it's ready, plus the harvest after that, discounted by even more time, and so on, forever. Then you add the value from a developer that thinks, "this plot is really close to Townsburg, and I could build houses here that would get annexed". So you add the value of the land as residential housing, times the probability IP would sell to the builder.

It's the same for food. Most farmland is rather far away from anywhere people might want to build houses. The few houses that exist nearby are only there because the people that live there need to be closer to the open land than the cities. So if it stops being useful for growing food, it's value drops to the next-best use, which is probably not housing. One of those uses might be preserved wildlife habitat. It all depends on where it is, and what it's next to, and the perceived value of a particular use.