Permaculture Designers Manual
CHAPTER 2 – CONCEPTS AND THEMES IN DESIGN
Section 2.7 –
Permaculture Pyramids Food Webs Growth and Vegetarianism
A figure often used to explain how much of a food or forage is needed to grow another animal is the trophic pyramid.
While the pyramid is a useful concept, it is very simplistic, and in all but laboratory conditions or feed-lot situations, it is unrelated to field reality, and may only apply where we actually provide simple food to captive species. The field condition is very different (See Figure 2.6).
Figure 2.6 Trophic Pyramid
Life systems are rarely strictly hierachical as in the Pyramid Structure. Most species are omnivorous and all species recycle valuable waste products to lower levels on the trophic ladder. Thus, life systems are a web or cyclic systems rather than a pyramid.
The pyramid is often used to support claims that we should all become “vegetarians“, or “herbivores“.
This is perhaps not so far from the truth, but there are real-world factors to consider.
I have shown the pyramid and also a direct path (herbage to human) to illustrate how we would support more people if we ate vegetation. But we need to re-examine this concept for people who return their wastes to gardens.
There are the following factors to reconsider:
NATURE IS MUCH MORE COMPLEX than is shown in a pyramid
Instead of simple “trophic levels“, we have a complex interaction of the same species, largely governed not by food habits, but by pasture management practices. Such a complex diagram is called a food web and is the normality in field conditions.
PYRAMIDS IGNORE FEEDBACK
In a very real sense vegetation eventually “eats” grasshoppers, frogs, fish, and people. Not only that,but as an animal grows, it returns nutrient to the soil via excreted, moulted, or discarded body wastes, and even if the frog eats 10 kg of grasshoppers to make one kilo of frog, it doesn’t (obviously) keep the 10 kg in a bag, but excretes 9 kg or more back to earth as manures.
This causes more vegetation to grow, thus producing more grasshoppers. The manure from insect “pests” may be the basis of a regenerative future evolution .
With these obvious feedbacks, the web itself becomes much more complex, and it starts to resemble less of a one-way staircase (the pyramid ) than a series of cydic events; less of a ziggurat and more like a spider’s web. So that the real position is that waste recycling to herbage is the main producer of that herbage.
WHAT OF MATURITY?
If our fish (level 4) was a carp, and that carp was more than a year or two old, then it would probably have reached full size, although it may then continue to live for another 80-100 years. So now, the carp (at 80 years old and 10 kg weight) has eaten 100 x 10 kg = 1000 kg of frogs and insects, and has returned 990 kg of digested material per year to the pond, to grow more herbage.
Thus, in order to keep the system in growth, we must be able to efficiently crop any level just before maturity is reached. We can see that old or mature systems no longer use food for growth, but for maintenance. So it is with mature fish, frogs,forests, and people.
Old organisms thus become constant recyclers (food in, waste out) and cease to grow, or they even begin to lose weight. This is why we try to use only young and growing plants and animals for food, if food is scarce. An exception is a fruit or nut tree, where we consume seed or fruit (seed is an immature tree).
ARE FOOD CHAINS SO SIMPLE?
We know that people normally eat vegetation, and that many people eat grasshoppers, frogs, fish, and (at times) other people. Even a cow eats grasshoppers as it eats grass, and of course every eater ingests large quantities of bacteria and small animals living on vegetation. “Man cannot live by bread alone“, unless in a slerile laboratory condition!
As our one-way pyramid is very suspect, so is the argument that we should become vegetarians to ameliorate the world food shortage problem. Only in home gardens is most of the vegetation edible for people; much of the earth is occupied by inedible vegetation.
Deer, rabbits, sheep, and herbivorous fish are very useful to us, in that they convert this otherwise unusable herbage to acceptable human food. Animals represent a valid method of storing inedible vegetation as food.
If we convert all vegetation to edible species, we assume a human priority that is unsustainable, and must destroy other plants and animals to do so.
What we eat is destroying both our bodies and the planet, according to author Lierre Keith, a recovering twenty-year vegan. While she passionately opposes factory farming of animals, she maintains that humans require nutrient-dense animal foods for good health.
A grain-based diet is the basis for degenerative diseases we take for granted (diabetes, cancer, heart disease) – diseases of civilization. Annual grain production is destroying topsoil and creating deserts on a planetary scale. Lierre urges the restoration of perennial polycultures for longterm sustainability.
In the urban western world, vegetarianism relies heavily on grains and grain legumes (e.g. the soya bean). Even to cook these foods, we need to use up very large quantities of wood and fossil fuels. Worse, soya beans are one of the foods owned (100% of patent rights) by a few multinationals.
They are grown on rich bottomland soils, in large monocullural operations, and in 1980-82 caused more deforestation in the USA and Brazil than any other crop. Worse still about 70% of the beans were either fed to pigs, or used in industry as a base for paint used on motor vehicles!
Much worse again, grains and grain legumes account for most of the erosion of soils in every agricultural region, and moreover, very few home gardeners in the developed world ever grow grains or grain legumes, so that much of what 15 eaten in the West is grown in areas where real famine threatens (mung beans from India, chick peas from Ethiopia, soya beans from Africa and India).
Old farmers and my own great-grandfather had a saying that bears some consideration.
“We will sell nothing from our farm that will not walk or fly off.”
In effect, the farmer was concerned to sell only animals, never crops or vegetation, because if the farm was to survive without massive energy inputs:
“animals were the only traditional recycling strategy for a sustainable export market.”
What does all this mean to concerned and responsible people in terms of their diet and food habits, with respect to a sustainable natural system?
Vegetarian diets are very efficient, providing:
They are based on easily cooked or easily processed crop grown in home gardens;
- That wastes, especially body wastes, are returned to the soil of that garden; and
- that we eat from where we live, and
- do not exploit others or incur large transport costs.
Omnivorous diets (any sort of food) make the best “Complex Natural Systems“; that we should eat from what is edible, at any level (except for other people in most circumstances, and under most laws!)
Primarily carnivorous diets have a valid place in special ecologies, such as areas of cold, where gardening cannot be a sufficient food base; in areas where people gather from the sea; where harsh conditions mean reliance on animals as gatherers; and here animals can us otherwise-waste products, such as vegetable trimmings, scraps, or rejected or spoilt vegetation.
“We should always do our energy budgets.”
Whatever we eat, if we do not grow any of our own food, and over-use a flush toilet (sending our wastes to sea) we have lost the essential soil and nutrients needed for a “Sustainable Life Cycle“.
While a tropical gardener can be very efficient and responsible by developing fruit and vegetable crop which needs very little cooking, sensible omnivorism is a good choice for those with access to semi-natural systems.
“City people using sewers would be better advised to adopt a free-range meat diet than to eat grain and grain legumes.”
Better still, all city waste should be returned to the soils of their supply farms.
Even in our garden, we need to concentrate on cycles and routes rather than think in pyramids. Simplistic analysis of trophic levels fails to note that some food resources are unusable by people, either because the energy needed in processing is too much (since some products of nature are poisonous or unpalatable foods), or because the resources are too scattered to repay our collection.
Such resources are often harvested into useful packages by other species.
Herons, themselves edible, eat poisonous toadfish, and goats will browse thorny and bitter shrubs. Thus we can specify these useful conversions therefore blindly eliminating a life element “of any type” from our diets.
While it is manifestly immoral to feed edible Peruvian fish to hogs in the USA, it may be of great value to convert forest acorns (unharvested in the USA) to hogs, and let the pilchards and anchovies feed the hungry of Peru (which includes the pelicans!)
The trophic pyramid is valid enough as a conceptual model, for we can see that poisons at the base concentrate at the top. In fact, the highest level of some radioactivcs and DDT measured are found in mothers milk.
We can see that the generalized or omnivorous (non-selective) feeder is blurred from catastrophic famine by a complex web of trophic connections, so that some losses and some gains accrue to people, being generally omnivorous.
In short, people need to discard fixed ideas, examine their kitchen cupboards, and try to reduce food imports, waste, and energy loss.