Fruit Walls: Urban Farming in the 1600s
lowtechmagazine.com
lowtechmagazine.com
The pessimist in me says "because these things would last centuries with a little upkeep, and we don't build that kind of thing anymore". Too hard to take advantage of short-term opportunities to repurpose or sell the land if you've put expensive, permanent(-ish) infrastructure on it.
They wouldn't. You're building miles of thick stone walls exposed to the elements, which you are deliberately forcing plants to cover as much of them as possible. The article and the followup hint at the repair and labor costs (note that the article is set in China):
> The decline of the European fruit wall started in the late nineteenth century. Maintaining a fruit wall was a labour-intensive work that required a lot of craftsmanship in pruning, thinning, removing leaves, etcetera. The extension of the railways favoured the import of produce from the south, which was less labour-intensive and thus cheaper to produce. Artificially heated glasshouses could also produce similar or larger yields with much less skilled labour involved.
This should not be surprising, since if fruit-walls were strictly superior, why were they ever obsolesced? In general, when reading sustainability fetish material like this, you should remember that these sorts of things are like code-golfing or min-maxing: schemes which place unrealistic value on just one dimension, and which can be highly interesting in how one maximizes that dimension, but are only rarely optimal under a more realistic set of tradeoffs. In this case, the fetish is for energy use while running, and mostly ignoring capital, repair, space, and labor costs.
Here are some of the current materials that we have that they didn't:
1. Concrete ( reinforced ) - much more durable than brick and mortar.
2. Mechanized vehicles like backhoes and the such to build walls
3. Better materials to trap and retain heat.
Probably others as well.
We also now have a global warming problem and other externalities that make greenhouses' energy inefficiency bad for society.
You know that "energy fetish"
Unfortunately, in most urban settings, both labor and capital are priced at a premium, so you get hit on both sides. When/where this was used, capital might have been constrained, but labor was generally not.
Capital, when taking on the form of land inflation, inflates the cost of labor, and often beyond direct energy costs. You end up with perverse incentives where quickly burning energy in the short-term will temporarily (for a lifetime or so) put you ahead of the economic game but put you quite substantially behind on overall energy sustainability if you start discriminating energy sources on generational EROI. I am beginning to wonder if The Great Filter is simply that galaxy-wide, any spacefaring-capable species wiped themselves out by economically exhausting all their high-grade energy before getting into any position in space where transferring much higher capacity high-grade energy from their sun was feasible.
On a recent tour of hydroponic growers in Almeria, Spain, I was told that province alone had 30,000 hectares in commercial greenhouses.