I live in a rural part of northern California in a county named Mendocino. There are about 90,000 people here, in an area of about 3500 square miles, for a population density of 25 people per square mile.[i] This is considered, and it feels like, a low population density. So naturally I think most people assume that if we had to grow our own food here we absolutely could.

But as a data-driven empiricist, I wanted to do the math on this. I posed the question: Could the land-base of Mendocino County support its current population of people if it needed to? This initial question leads to many others, including: What is the theoretical diet being consumed? What are the yields per area of the parts of the diet? What kinds of soil, water and energy systems are needed to produce those yields? And, do the requisite land-water-energy resources exist at the levels implied by the diet demands?

If you don’t live here why should you care about an analysis done for Mendocino County? Well, the point is that this exercise can be done any place and is generally instructive on how our diets are dependent upon a whole suite of resources. How do you feel about the future of those resources globally, nationally or closer to home? Does thinking about these topics, running the numbers and considering scenarios influence your thoughts about where to live, who to talk to, and what to invest in?

Before I get into those questions, it is important to explain some of my basic operating assumptions. First, I am interested in this question for a number of reasons that revolve around energy and security. I believe that global energy availability will decline this century as fossil fuel reserves are depleted. I also believe that burning those fossil fuels is a bad habit anyway since they muck up the climate system upon which food production depends. Now, amazingly, our current food production, distribution, storage and preparation systems are highly dependent upon the very fuels that are going into depletion and spewing pollution into the environment.[ii] When envisioning what it means to produce food in the future for Mendocino County I therefore assume a low energy input agriculture, meaning organic fertilizers, limited irrigation, and local distribution systems. As it turns out, this is also the system that would produce the fewest greenhouse gas emissions. I don't want to argue about the merits of conventional vs organic methods, or localism vs globalism in trade, but simply state my position that whether out of necessity or moral choices, the only option for sustainable production of food over the long-term is through relatively local and organic systems.

Quite astonishingly to me, the potentially important goal of local or bioregional food self-sufficiency is rarely considered. For example, my chin almost hit the floor at a climate change conference in Sacramento a few years back when the following actually happened. A senior professor of hydrology from UC Davis gave a presentation of what looked to me like severe water shortages in California due to climate change melting winter snow packs, not to mention the potential for severe flooding of the Central Valley, one of the most important agricultural regions on the planet, from sea level rise. The maps he showed of the havoc-ridden area included a complete build out of the Central Valley into suburban housing, which was presented as sort of a pre-ordained eventuality. When someone pointed out to him that it looks like there's almost no more food production in California in this scenario, and that the state would, under the conditions of less water, higher seas, longer and more severe heat waves, etc. still have 60-90 million people to be fed, which begs the question where might their food come from he replied, "We'll import it." As far as I could tell, this position was the standard one not only of the academics in the room, but of the state bureaucrats organizing the event.

In any case, soon afterwards I began exploring some alternative scenarios, one of them a few years ago being a rough estimate for what food self-reliance would entail around here.[iii] Recently others have done similar work, such as analyses for the state of New York[iv] and Britain.[v] Not having a degree in agriculture I don't feel highly qualified to do this, but I do have a doctorate in biology and am comfortable with basic math and spreadsheets. I have also become a vegetable farmer recently, so do have some personal expertise in a limited aspect of food production. If readers find glaring errors, poor assumptions or better data I am keen to hear about it. As a scientist, my main goal is to get as close as possible to the truth, wherever that leads.

The Diet

Every locale has a combination of climate, soils and culture that when combined with other assumptions related to future energy and food system methodologies will limit the reasonable range of food species available. It is difficult to be purely scientific in this situation because what people prefer to eat is governed by personal taste and physiology. So I made some judgment calls when proposing the basic mix of foods given a local, sustainable system in place. Keep in mind I am also considering this from a population level. So while some may see "beef" and say that they are vegans, or see "dairy" and fuss about their food allergy, that is beside the point.

Human nutrition is highly complex and controversial. In this case I envisioned a culturally appropriate healthy diet based on a mixture of factors and guiding principles, including: (1) maximizing food diversity, (2) emphasizing fresh produce for vitamins and minerals, (3) considering the relationship between soil health and rotation among production types (e.g., pasture and field crops), (4) the importance of food storage, and (4) the weight of food ingested per day. I also set a goal to produce close to 3000 calories per person on average. The population can get by with less, perhaps 2400 calories per person, but food waste can't be totally avoided and good years may be followed by bad ones. Food is so important that we should plan for excess just in case. This is common sense and used in engineering all the time, such as building the bridge a bit stronger than the maximum load it is supposed to carry.

With that lengthy explanation, I offer the following table of foods, their proportions, and how they form a complete diet at an individual level. Each row deserves some further discussion.

Because of our winter rains and dry summers, grains will be dominated by plants with C3 metabolic pathways, chiefly wheat, rye, oats and barley, also known in the trade as "small grains." By contrast, corn, sorghum and rice would require summer irrigation for high yields.

Dry beans can also be grown in the cool season if lentils and chick peas are chosen. Pinto types are summer-irrigation dependent. For both grains and dry beans I will assume yields from dry-land (i.e., non-irrigated) methods. Irrigation could potentially double yields.

My calculations for oil use olives. I prefer olives because, unlike field crops, they can be established on non-tillable soils and so don't necessarily compete for prime ag lands. Trees can also find deep water sources and may not require irrigation once well established. Olive oil is also versatile and prized for its flavor.

Honey is the sugar source in my diet mix. Other potential sugars include sweet sorghum and sugar beets. I prefer honey because of lower processing costs relative to sugar crops, and honey bees are synergistic with food crops rather than competitive for land area. About one hive provides enough sugar per person.

Sprouting seeds are included as a storable and portable source of high calories and nutrition, including vitamin C. The crop modeled in this diet plan is sunflowers. I like sunflowers because they are a prolific summer source of nectar for honey bees, they can be used as an oil crop if necessary, and they produce good biomass in stalks and seed heads. Tree nuts could also be included/exchanged in this part of the diet and have the advantage of not always needing prime ag land.

Fruit and vegetables are a diverse assortment of standard crops, including lettuce, cabbage, potatoes, carrots, grapes and apples. The caloric density ranges about 10-fold (zucchini, 64 calories/lb, garlic 676 calories/lb) but averages 200/lb when calorie staples such as potatoes are included.

Dairy calculations are based on a soft cheese, such as mozzarella, which has 3 times the caloric density as whole milk. The allotment here is equivalent to 1.6 cups of fresh milk a day, but cheese is used for ease of comparisons among mostly sold foods. Cheese also stores and transports well so should be encouraged. In reality I'd expect a mixture of consumption patterns, such as a cup of milk a day and a modest piece of cheese.

I am using chicken eggs, about 1 per day per person.

Meat assumes domestic animals such as fowl and ruminants. I prefer rotational grazing systems that mimic multi-species flocks. Chicken is less calorie dense than beef, so an average is used. The most common livestock here are cattle and sheep, so I will likely emphasize their needs when calculating land area though other species warrant consideration. The amount of meat in the diet, 50 lbs per year, is about 1/3 the current U.S. average and works out to 2.2 oz per day, or just under a pound per week. I am not expecting people to eat tiny portions of meat each sitting, but perhaps a pot roast or leg of lamb shared among a family on Sunday dinner. While this quantity of meat seems low by current U.S. standards it is the same as modeled for an area-efficient diet in New York State and would be the envy of many parts of the world.[vi]

An additional factor when considering a diet is the total weight of the foods being consumed each day. Human stomachs get uncomfortable when given too much food, so foods with high caloric density offset the weight of foods with low density. Some foods are eaten with their natural content of moisture, whereas others are stored dry and are hydrated during cooking. The table multiplies the dry weight of certain foods (grains, dry beans and sprouting seeds) by a factor of three to estimate their weight when ingested. Keeping the diet below 6 lbs per day is a goal.[vii]

I like this diet because it feels normal to me, and appears very healthy. A quarter of the daily weight of food is in the form of fruits and vegetables (Fig. 1). Eggs, dairy and meat are present but not in unhealthy proportions. Oils and sugars are recognized as important but their presence is moderated appropriately. Whole seeds are the main caloric staples, including cereals, legumes and other seeds (Fig. 2). I would like a nutritionist to look this over and let me know if I am especially high or low on anything in their view. Overall, I think I struck a nice balance that will likely provide enough calories, protein, minerals and vitamins without excessive food weight (5.2 lbs per day), using a mix that stores well and is culturally familiar.

Fig. 1. The daily wet weight (ounces) of food is given by food class.

Fig. 2. The daily calories of food are given by food class.

Okay, so step 1 is complete, establishing a diet. The next steps are: (2) translate this diet into land area requirements, (3) scale the land area from an individual level to the population of Mendocino County, and (4) compare to the actual land-base.

[i] http://www.city-data.com/county/Mendocino_County-CA.html

[ii] http://www.cias.wisc.edu/pdf/energyuse.pdf

[iii] http://www.willitseconomiclocalization.org/files/well/FoodSecurityReport.pdf

[iv] http://www.news.cornell.edu/stories/Oct07/diets.ag.footprint.sl.html

[v] http://transitionculture.org/wp-content/uploads/2007/CanBritain.pdf

[vi] http://www.news.cornell.edu/stories/Oct07/diets.ag.footprint.sl.html; and original article here: http://www.journals.cambridge.org/action/displayAbstract?fromPage=online&aid=1091328&fulltextType=RA&fileId=S1742170507001767

[vii] Duhon, D. 1985. One Circle: How to Grow a Complete Diet in Less Than 1000 Square Feet. Ecology Action, Willits, CA.