Feasible population densities for self-sustaining communities?
Hi Dave,
My wife, Nicole, and I have taken the three day "Grow Biointensive" course with John Jeavons. In this course, we learned what it would take to grow a complete diet, including grains, pulses and compost crops, for one person for one year.
According to his calculations, you can grow a complete diet for yourself, including growing the compost materials to maintain and even enhance the yields over time, on 4,000 square feet of land. I believe this is for a four or five month growing season. If you have a longer growing season, you can grow nothing but food crops and then in the second half of the season, you can grow compost crops on about 2,000 square feet of land (with intermediate "Grow Biointensive" yields).
4,000 sqft is about 1/10 of an acre.
Jeavons' thesis is that, assuming continued population growth, we will quickly reach a point where there is less than 4,000 sqft of usable land per person on this planet, never mind oil depletion!!! (but the population might take care of itself as economies collapse, and people start eating soylent green). So he has spent the last 30 years studying how much land it takes to grow a caloric and nutritionally complete diet for one person. Naturally, this is a vegan diet since you have to grow the feed to feed the hypothetical livestock when you could use it directly to feed yourself. Livestock is "out" in his model.
BTW we live at the Greater World Earthship subdivision near Taos, New Mexico. All the homes provide all of your utilities using nothing but sunshine and rainfall that strike the house.
I have created a website: www.greaterworld.org
that tells a little more. It is still in a rudimentary state, but I will get more people to contribute content to the site!
Our main issue is water. How can we route and store enough water to grow a complete diet for ourselves?
Zac H.
Zac,
Thanks much for your response. Jeavons' "biointensive" methods sound very interesting--I'll look into that.
4000 sq ft is about 63 feet on a side. If 4000 sq ft will really produce an annual diet for one, then many subdivisions perhaps could become food-sufficient (especially with most streets removed).
Yes, water would be a challenge in many areas, including around here, especially if one doesn't want to count on the water-distribution infrastructure remaining functional over time. If you build storage cisterns and erect maximal, temporary rain collection surfaces during rains, would that help? I'm thinking poles, parachute cord and stakes, supporting plastic sheets. Then you could use the water when and where you need it. I guess, based on annual rainfall, you could calculate the maximum water you could possibly collect this way, but to catch the maximum would require an astronomical surface area. And, if its windy while raining, this would be a challenge for using plastic sheets. In this respect, I wonder how self-sufficient truly arid regions could really be? Water certainly limits net primary production of natural ecosystems in arid regions--its a big challenge for you! Your community sounds interesting--I look forward to checking out your web site.
Dave W.
Hi Dave,
If a place gets about 30 inches of rain per year, most of it during the growing season, you'll have it made. There are maps available online that show annual and monthly rainfall averages for the continental US. At a glance, you can see where promising places to live are. Here's a great webpage for precip data:
http://www.ocs.orst.edu/prism/products/matrix.phtml?vartype=ppt&view=map...
Our home has about 1,500 sqft of floor and roof area. If one inch of rain fell, our roof should intercept about 1,225 gallons of water.
We just had 0.55" of rain on April 28 and that added about 600 gallons of water to our cistern.
Last year was a wet one and from March 10, 2005 to March 10 2006, we got 10.5". Our cisterns overflowed on several occasions.
For food production, however, you need gobs of water, ON DEMAND, in order to get decent crop yields. If you can get 0.2" of water on the soil each day, you'll get good crops. In most places, you'll need to store water or pump it from a well or divert it from a river or some such.
I've heard from some people that you can go as low as two inches of precip/month and still get a crop but it'll probably take special precautions to absorb and conserve that moisture.
About 1,500 years ago, the Nabatean of the Negev desert werwe able to grow grains and orchards on about half the rain we get here at the subdivision! They did some very clever things to direct runoff water into cisterns mades of stone and plaster.
If they can do it on about 3.5" annually, we should be able to do it here with 7 inches of precip (I really don't know what is typical out here. Nobody has measured the precip every day for years on end). I'm probably the first one to collect over a years worth of solid data.
The Nabateans have a leg up on us because their soil structure was such that it forms an impermeable crust after a rainfall and, afterwards, the water just sheets off like crazy.
They were also able to easily carve out cisterns from thick beds of chalk to store gobs of water from the few storms they get each year.
We'll probably have to do some kind of treatment of the rain catchment area to increase the efficiency of water sheeting off into a storage cistern.
That would be really cool if you could roll out huge tarps just before a rain and get 100% collection efficiency!
If you had low growing vegetation, like blue grama grass, or similar, it wouldn't be hard to roll it out but the winds...my God! ;-)
The trick to getting runoff, in general, is the rate at which the rain falls. If the precip rate is approach one inch per hour, water starts to runoff in clay soils poor in oganic matter such as here.
I will continue this at a later time. Right now, I need to get to bed and start work tomorrow!
Cheers,
Zac
Has anyone tried to calculate how much land per person would be needed by a group of people living mainly by intensive farming in different parts of the U.S.?
I read in "Five acres and independence" that a cow requires at least an acre of pasture, so I'd say cows are out!
I'm thinking in terms of human-labor-intensive farming, chickens, probably a goat or two, and fish culture (tilapia?). If you take a piece of suburbia, rip out all the asphalt and concrete for farming, capture as much rainfall as possible and use it carefully, and perhaps even condense into higher living densities in fewer houses (converting dismantled house space into farming), would it still be necessary to greatly reduce the population density of the neighborhood in order to arrive at a people-per-food-production figure that allows the group to grow essentially all their own food? I suspect probably so.
Dave W.