Ecovillage Question 3

From CFI

Researcher

Jason Bradford jcbradford@ucdavis.edu 707-456-0760

Question

How many people can we put on a particular parcel (in the context of an ecovillage) given its size and productivity?

Assumptions

Outside material resources insignificant; community self-sufficient given the land they inhabit and that which comes to them via the atmosphere and hydrosphere. Population density mainly determined by an agrarian/horticultural means of subsistence, only modestly enhanced by hunting and gathering of locally available resources. Methods of food, fiber and fuel production are sustainable so that the land does not become spoiled and less productive over time. To remain cautious and promote long-term security, about half the area is designated “wilderness.” This will provide some supplements to the agrarian base, and, more importantly, add stability and resilience to the landscape and act as an “escape valve” if land-use proves unsustainable.

Answer

Ideally, an available area of land would have a diversity of landscape features, such as upland forests and grasslands, riparian zones, and established agricultural areas. Under this scenario, the agricultural area would determine the population number as long as it is less than or equal to 50% of the total area. Suitable agricultural area is determined by both the quality of soil, workable topography, and water availability. If most crops are grown during the warm/dry season, about 50,000 gallons of water storage or ground pumping per person is needed for food (Jeavons, 2004a). However, this may be an overestimate if winter cropping is used and produces a significant fraction of the diet. Using the estimate of 1/5th of an acre per person (Bradford, 2004), the following formulas may be applicable:

Steps:

(1) Total land area in acres/2 Gives half to “wilderness” (2) Remaining acres arable land x 5 Gives upper limit to population based on area (3) Total water available in gallons/50,000 Gives a limit to population based on water, assuming warm season agriculture

Chose lesser of either 2 or 3 for total population allowed.

For example, a 160 acre parcel would have 80 acres set aside for wilderness. Assuming sufficient water and the other half suited for agriculture, about 400 people could be accommodated. However, if warm season agriculture is the means of subsistence and 10 million gallons are available, 200 people are possible. These calculations incorporate the need for housing and other infrastructure within the 1/5th acre per person figure used.

The formula above is conceptualized for food production. Fuel and fiber production should also be a goal, and if done in the context of an intensively managed agricultural system, this would add another 80% to the area and water requirements (Jeavons, 2004b). Therefore, another formula set taking this into account may be:

Steps:

(1) Total land area in acres/2 Gives half to “wilderness” (2) Remaining arable land x 2.8 Gives upper limit to population based on area (3) Total water available in gallons/90,000 Gives a limit to population based on water, assuming warm season agriculture

Chose lesser of either 2 or 3 for total population allowed.

Another approach might be to dispense with a strict division between agriculture and “wilderness” and have a transition zone consisting of primarily perennial plants that have been selected for their usefulness to humans (Holmgren, 2002). These might include fruit and nut orchards as well as native species admired for their properties (e.g., oaks, willows). This portion of the landscape would be similar to the “wilderness” in that only natural rainfall would be available. Given that water is such a limiting factor in our summer, perhaps, at the very least, fiber and fuel needs can be accommodated in this way.

More information is sought on the potential for winter grains and legumes in Little Lake Valley to provide food for people. The calculations used above are largely ignorant of this potential, which may be significant. If these are important sources of food, it takes pressure away from developing large and complex water storage and delivery systems to use during summer months. An agricultural landscape consisting of large areas sown in winter grains and legumes followed by much smaller areas for summer crops may be most efficient. Deep-rooted perennials, as described above, would augment this with fruits and nuts. A third formula on population capacity awaits this information.

Sources

Bradford, J. (2004). “How many acres of land are required to feed the approximately 10,000 people in the Little Lake Valley region?” Food Question 1

Holmgren, D. (2002). Permaculture: Principles and Pathways Beyond Sustainability. Holmgren Design Services, Hepburn, Australia.

Jeavons, J. (2004a). A Complete Closed-System Mini-Farm. Ecology Action Basic Workshop Manual, 7. Water/Arid/Tropic.

Jeavons, J. (2004b). A Complete Closed-System Mini-Farm. Ecology Action Basic Workshop Manual, 11. Planning.

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