I disagree with Samo's idea of catastrophic decline dropping below baseline. Especially your idea of loss of irrigation reducing farmland to desert immediately. I liken it more to the concept of a sine wave. The decline, the falling slope of the wave is equal but opposite to the rising slope.
I don't know if there's a social parable to this. But actually, farming land, provided fertilization has taken place—contrary to non-agriculturalists ideas—actually leaves the soils in better shape than previous virgin land due to increased organic matter, carbon sequestration, increased microbes, etc.
I disagree with Samo's idea of catastrophic decline dropping below baseline. Especially your idea of loss of irrigation reducing farmland to desert immediately. I liken it more to the concept of a sine wave. The decline, the falling slope of the wave is equal but opposite to the rising slope.
I don't know if there's a social parable to this. But actually, farming land, provided fertilization has taken place—contrary to non-agriculturalists ideas—actually leaves the soils in better shape than previous virgin land due to increased organic matter, carbon sequestration, increased microbes, etc.
EDIT: Samo's idea, not Your idea.