Introduction to agricultural systems



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Hierarchy. Each of these systems is hierarchical - each system is nested within a larger system. For example, plant/soil systems form ecosystems which form biospheres which together form the biophysical systems of the Earth.

Emergent properties. New properties of a system emerge as you move from one level to the next. As you move from the plant/soil system to the ecosystem level, consumers (herbivores and carnivores) enter the picture, and the food web must be described in a new way. Moving to the biosphere level, information about the relationships among ecosystems emerge, which show, for example how important forests are in maintaining the CO2 and O2 levels in the atmosphere, and the role of grasslands in sequestering C in soil organic matter.
2.1.6 Barry Commoner's Four Laws of Ecology (Commoner, 1971, pp.33-48)
1. Everything is connected to everything else.

2. Everything must go somewhere.

3. Nature knows best.

4. There is no such thing as a free lunch.

2.1.7 Succession in Natural Systems (Reading 5: Miller, 1986, Chapter 6)

Refer to Figures 1-7 and 1-8 from Cox and Atkins, 1979, p. 50-52 and Smith, 1974, p.258.

Ecosystems change with time. They originate, develop and mature, as represented by progressive changes in species structure, organic structure (nutrient cycling) and energy flow. The change is called ecological succession. Succession proceeds as the plants and animals of the ecosystem interact with its resources towards a steady-state system (climax). It involves a gradual and continuous replacement of one kind of plant or animal with another, with the community gradually becoming more complex. Succession is driven by feedback mechanisms (Figure 1-7).

The organisms themselves modify the environment by creating a habitat suitable for themselves. Over time, they are gradually replaced by a different group of organisms more able to exploit the new environment.

In early successional stages, energy is channelled through few pathways to many individuals of a few species, production per unit area is high, and food chains are short, linear and based on grazing. A high proportion of the energy captured as sunlight goes into plant production (net primary productivity is high), increasing the biomass of the community. Because there is little organic matter stored in the soil, on the soil surface, or in trees, there is very little biomass in the system compared to the amount of energy used to make new living tissue.

In late successional stages, energy is channelled down many diverse pathways and shared by many species. Food chains are complex and mainly detrital with many organisms living on the carbon fixed by the relatively few primary producers. Because there has been a long period of biomass production and storage in these systems, the amount of biomass relative to the amount of energy used to make new tissue is high, and energy is being used more efficiently in biomass production. It takes less energy to support a given biomass in late successional stages. Organism diversity increases with maturity, as does the complexity of food webs.



Table 1. Stages in Ecosystem Development (Smith, 1974, p. 262).

Attribute Young Mature



Biomass Small Large

Gross production:community respiration >1 ot <1 ~1

Gross production:biomass High Low

Biomass supported per unit of energy flow Low High

Food chains Short, grazing Long, complex, detritus

Stratification Less More

Species diversity Low High (?)

Niche speicalization Broad Narrow

Feeding relations General Specialized

Size of individuals Smaller Larger (?)

Life cycles~ Short, simple Long, complex

Population control mechanisms* Physical Biological

Fluctuations More pronounced Less pronounced

Mineral cycles Open More or less closed

Role of detritus^ Unimportant Important

Stability Low High

Potential yield to humans# High Low



~ Young systems are dominated by annuals, perennial plants are more common in older systems.

* Population limits are climate and soil resource based in young systems - in older systems, rate of nutrient cycling becomes more important.

^ Soil organic matter

#Cropland is mainly kept at a young stage of succession - largely through repeated disturbance of the system.

Diversity is related to stability. Efficient ecosystems accumulate biomass within a large number of individuals of a few species (i.e., crop land), and as a result are not stable. Because of the small variety of species, they are subject to disturbance that can disrupt the whole ecosystem. In diverse ecosystems, disturbance to one component or species does not disturb the whole system because there are many other pathways for energy transfer. Diverse systems are stable, but less productive. Thus, the price of stability is productivity, and the price of high productivity is instability.


Disturbance. Succession functions when disturbances (fire, earthquakes, animal holes, large herd grazing, serious drought, flooding, ice age) change the system. It is a regenerative process. For example, after the last ice age in the Prairie region (10,000 years ago), only bare ground remained as the glaciers retreated northward and the environment warmed. Pioneer species that can withstand severe physical conditions colonized the bare ground. They modified the environment to make it more suitable for other species by producing soil organic matter and systems of nutrient cycling, and by reducing soil erosion due to wind and water. As new species colonized the area, the pioneer species gradually die out.

As the system matures, accumulated biomass increases relative to primary production, nutrient cycles are completely developed, and the system approaches a steady-state that is comparatively stable. The ecosystem will remain in a steady-state until it is again disturbed.

Disturbance is a natural part of a natural ecosystem. It allows for the release of nutrients tied up in plants or soil organic matter. For example, fire was an important mechanism for rejuvenation of the grassland ecosystem on the Prairies. Without periodic fire, plant litter would continually accumulate, tying up nutrients and reducing plant production. The whole grassland would have reached the stage of climax vegetation, with uniform stands of climax species everywhere. Burned areas return to earlier stages of succession, providing differences in habitat quality and releasing scarce nutrients back into the system. Unburned parts of the grassland remained in a steady-state until litter accumulation was large enough to fuel a fire, and then they too burned.

In natural systems, disturbance can be large-scale (fire or glaciation) or small-scale (aminal burrows or soil erosion on the shoulder of knolls), but in both cases, it functions to ensure that the whole ecosystem does not reach climax at the same time. That can be a problem in managed park areas where fire is suppressed, and all of the forest or grassland reaches a climax stage. At that point, old trees begin to die or large amounts of grassy litter accumulate, making the whole area very susceptible to fire, and not small patchy fires that only burn the oldest areas with the most fuel, but very large fires that become hot enough to burn an entire region of forest or grassland.

2.1.8 Natural systems as models of sustainability

It is important to study natural systems because they are the only examples of sustainable systems that we have. In many areas of the world, where settled agriculture has been practised for a long time, there are no natural systems left. In North America, we can study the few remnants of natural systems that remain in order to understand what makes them sustainable, and to understand the feedback mechanisms that allow them to continuously function within the limits of their environment.



If we accept that there are serious environmental problems (climate change, increased carbon dioxide and ozone depletion in the atmosphere, pollution, damage to ocean systems, damage to terrestrial systems), the only way to address those problems may be by understanding natural systems and modelling our agricultural and other systems on natural systems.

Definitions of sustainability:

  1. The maintenance or even improvement, without degradation, of natural systems over the very long term (Munasinghe and Shearer, 1995, p. xviii).

  2. An ecosystem in which the internal dynamics of the ecosystem are, more or less, in a steady state - that is, they are not degrading over time. Primary focus is on the inputs and outputs and whether they are sustainable (Figure 1-5).

  3. State view: A sustainable ecosystem is one in which a state can be maintained indefinitely (ibid.).
  1. Capital or stock view: The amount of consumption that can be continued indefinitely without degrading capital stocks - including natural stocks (Costanza, 1991, p. 8). Natural capital is the soil, atmosphere, plant and animal biomass that form the basis of all ecosystems (i.e., forests, fish populations and petroleum deposits). Natural capital stock uses primary inputs (sunlight) to produce the range of ecosystem services and natural resource flows. The products of the ecosystem are used at a rate within that ecosystem's capacity for renewal (live off the income rather than the ecological capital). For example, population size at the top of the food chain is limited by amount of food at a lower level.


  2. Potential throughput view: Resources are used within their capacity for renewal. Sustainability is based on the maintenance of potential, so that ecosystems can provide the same quantity and quality of goods and services as in the past (Munasinghe and Shearer, 1995, p. xxii). An example of an ecosystem good would be fixed carbon or standing biomass; an example of an ecosystem service would be decomposition and the release of biomass nutrients to the soil for reuse by plants or the storage of precipitation in the soil for later uptake by transpiring plants. Potential is emphasized rather than stocks, biomass or energy levels. Maintenance of potential requires that the physical productive capabilities of the land and water (habitat maintenance) are maintained and that genetic diversity is maintained.

  3. General view: The maintenance of essential ecological processes and life-support systems, the preservation of genetic diversity, and sustainable utilization of species and resources.

Natural systems are inherently sustainable. Feedback mechanisms, self-regulation mechanisms, and adaptation ensure that the natural systems of the world can carry on forever, barring catastrophe, such as the impact of a huge meteorite that demolished half the planet. Sustainability is largely a natural state of affairs. Production of ecosystem goods is limited by the amount of solar energy reaching that system, the climate, nutrient availability in soils, etc., and consumption cannot exceed production.

Lack of sustainability is the result of social (human) actions.Non-sustainable practices and behaviour are associated with shortsighted people who undermine the ecological basis of their own lives or the lives of future generations (Munasinghe and Shearer, 1995, p. xx). In systems that are influenced by human 'development', sustainability involves complex interactions (environmental, economic, social, cultural and political), as people decide what is to be sustained, what plants should be produced, how much habitat should remain for other species, who should benefit from what is being sustained, etc. It is important to remember, however, that sustaining the basic global life-support systems is still a prerequisite for sustaining human societies.


Questions: As we study the agricultural systems, we should ask:


  1. Is this system sustainable?

  2. Can it carry on over the very long term without running out of energy, or using resources faster than they can be renewed?

  3. How do human systems fit into the natural system?


2.1.9 Reading: Only One Household (Ashworth, W. 1995. pp.23-30 in the Economy of Nature: Rethinking the connections between ecology and economics. Houghton Miflin Co., New York.
There is no longer anyplace on the planet that the environmental crisis has not reached.

The litany of damage is numbing. Waste products spewed into the atmosphere have altered the Earth's climate and opened holes in the ozone layer. Deforestation is taking place on a continent-wide scale. Rivers and lakes have become toxic cess­pools; even water from remote wilderness streams is often too polluted to drink. Groundwater resources are used up, con­taminated, or both, over much of the world. The air in our cities cannot be safely breathed. Garbage spills out of old, over­crowded landfills, and there is no place to put new ones. The gentle, life-giving rain has become sulfuric acid.

There is literally no place to flee. Not to the ends of the Earth; that is where the ozone holes are. Not to the equatorial jungles; they are falling to the axe so fast that, as an intact ecosystem, they are not likely to last out the century. Not to the floor of the sea; it is littered with household trash, and polluted dredge spoil, and canisters filled with radioactive waste and toxic chemicals, and a myriad of other things we have dumped there under the delusion that we were getting rid of them. And not even to the depths of the Earth; those too are polluted. For decades now, we have been injecting hazardous wastes into aquifers as much as 20,000 feet below the surface of the planet. According to current EPA and industry esti­mates, there are some six hundred active injection wells in the United States aloneCand upwards of forty thousand aban­doned ones. Approximately 60 percent of the toxic waste we produce in this nation is currently handled by this so-called deep well disposal method, which threatens groundwater sup­plies, alters the structures of subsurface rock formations, and has been known (in at least one thoroughly documented case, near Denver, Colorado) to cause swarms of earthquakes.

Nor can we successfully escape to those little bits of nature we have drawn lines around and explicitly chosen to leave undisturbed. Our parks and wilderness areas are in at least as much trouble as the rest of the planet. Two recently released studies demonstrate just how deep this trouble may be. An internal audit of the National Park Service conducted by the inspector general of the Interior Department found most of the thirty-three parks studied suffering from "serious and irre­versible degradation" due to Park Service budget priorities, which have for years been emphasizing visitor services (92 percent of moneys spent) over protection of park ecosystems (8 percent). And an even broader study by the National Acad­emy of Sciences, released on January 13, 1993, found "virtu­ally all" parks and wilderness areas in the United States suf­fering seriously from air pollution. "Scenic vistas in most U.S. parklands," stated the Academy, "are often diminished by haze that reduces contrast, washes out colors and renders distant landscape features indistinct or invisible." For parks and preserves established to protect scenery, this is more than a minor nuisance: it is an attack on the central reason for their existence.

These problems are by now widely recognized and endlessly talked about. What is not generally recognized or talked about is that they are economic problems as well as ecological ones.

The health of a society's economy depends to an overwhelm­ing extent on its relationship to its environment. This is true whether the economy is built on free trade or command-and­ control; whether the society's focus is material or spiritual; whether the resources it uses are obtained directly from the earth or through trade with other societies; or even whether or not the society is human. The birds of Alaska's Thigh Reef had a far healthier economy before the Exxon Valdez ran aground there than they had in the days and months immedi­ately afterward. Island nations such as England and Japan remain prosperous only to the extent that they can trade ideas, such as manufacturing know-how, for the products of other peoples' environments. Monks in monastic retreats must either labor in their own fields and vineyards or depend upon the largesse of a religiously minded people around them. Commu­nism fell in Eastern Europe in large part because the resource bases of those ancient countries had been so badly neglected and abused, in the name of "economic progress," in the four decades since the end of the Second World War.


All of a nation's physical resources come in some form or another from the earth. Food must be grown in the soil; lumber must be harvested from the forests; minerals must be ripped from the rocks or distilled from the salt-laden waters of the sea. There are no other sources for these materials. Even intellectual products derive ultimately from the environ­ment, for the mind is housed in the body and the body must be fed and clothed. All of usCcapitalist and communist, industrialist and environmentalist, pragmatist, reactionary, and wild-eyed radicalCall of us make our living only with what the earth gives us. It is the only way we can possibly stay alive.

So it has been through the centuries. Today, however, we are being told over and over that the source of an economy's wealthCits surrounding environmentCand the economy itself can not only be divorced from each other but are basi­cally antagonistic. Environmental protection "costs jobs" and leads to an outflow of capital from the protected area. Eco­nomic development "rapes the environment," leading to the loss of species diversity, the destruction of natural beauty, and, ultimately, human sickness and death. Here is Thoreau, muttering about a farmer "who would carry the landscape, who would carry his God, to market, if he could get any thing for him"; over there is Dan Quayle, complaining about Democrats who "put people first, unless there happens to be a spotted owl or a great garter snake or some other endangered species, and then that needs to have priority.... We must give priority to economic growth and the creation of jobs." On this side is the activist and vegetarian George Wuerthner, lambasting his fellow environmentalists for their carnivorous­ness: "You can't support wolf re-introductions in Yellowstone while consuming a big thick steak or be opposed to predator control if you chew on hamburgers." On the other side of the dietary fence stands Richard Darman, budget director for the Bush administration, telling the press emphatically that "Ameri­cans did not fight and win the wars of the twentieth century to make the world safe for green vegetables." The rhetoric rolls on and on, escalating as it goes, eventually reaching beyond rhetoric and into violence: fistfights in bars, spikes in trees, firebombs in environmentalists' cars, sand in the gas tanks of developers' bulldozers.

But if economic well-being and environmental protection are so strongly opposed, why is it that we so often find them together? Shove the rhetoric aside for a moment and look at the land. You will rapidly observe a striking correlation: ecologi­cally distressed areas are almost always economically distressed as well. This is most easily seen in urban sacrifice areas such as south Chicago, central Los Angeles, and east Newark, but it is equally true of rural America. From the coal country of Appalachia to the logging towns of the Pacific Northwest, in­dustries that have ripped wealth out of the land have left behind raw pockets of aching, bleeding poverty. The coincidence of a degraded, polluted landscape and a depressed economy in such places as Forks, Washington; Lake Linden, Michigan; Ham­mond, Indiana; and Pineville, Kentucky, is no accident; it is an integral part of the way we Americans have been doing things.

In contrast to the stagnant state of these economic and ecologic backwaters is the condition of such places as Santa Fe, New Mexico; Hilton Head, South Carolina; Davis, California; and Burlington, Vermont. These widely diverse areas all hold two things in common. They are places where strict land-use controls and other environmental regulations are in place, enforced, and supported by the people. And they are among the wealthiest communities in America. Property val­ues are high; local businesses are booming. Economic indica­tors are extremely healthy. Money is drawn to these areas precisely because they have taken care of their environments. Forests and streams as neighbors create good places to live. Steel mills and coal mines create bad ones. Straightforward market forces do the rest.



Environmentalists prepared to chortle over the failure of economic exploitation to provide economic success, though, had better hold their tongues. The unwelcome truth is that environmental protection has not really provided a sound environment, either. The Davises and the Burlingtons are pret­tier, cleaner, and healthier than the south Chicagos and the Lake Lindens; but under those shining, scrubbed facades the same dark problems hide. Our vast complex of laws and regulations, our widespread network of parks and preserves, and our libraries full of ecologically conscious literature have yet to do more than minor cosmetic damage to the juggernaut that is destroying the planet. We have dented a fender or two, but the bulldozers continue to plow ahead.

Despite the flurry of legislation following the publication of Silent Spring, pesticide use in the United States has contin­ued to climb dramatically, up from 648 million pounds per year in Rachel Carson's day to about 2.5 billion in our own. Fertilizer use has approximately doubled in the same period, rising from 25 million to 54 million tons annually. Twenty years of clean-water and clean-air legislation have left us with only marginally cleaner water and air. (In many places, it is actually considerably dirtier.) And though wilderness and park acreage is up dramatically, there is little evidence that this trend has improved the overall state of the environment. The gross forms of degradationCclear-cuts, freeways, minesChave not gone away, but simply shifted elsewhere. The more subtle forms have continued unabated, undeterred by human-cre­ated boundaries. Species diversity is down within the pre­serves as well as outside them, and air and water pollution are up. Acid rain respects no borders: there are at least as many acidified lakes within the "protected" area of the Adirondack Forest Preserve as there are in the rest of upstate New York.

When I first began hiking the wilderness trails of the Pacific Northwest, back in the early 1960s, I could stick a cup di­rectly into virtually any stream I came across, confident that the cold, clear, vibrantly fresh water would be safe to drink. Today one must carry a filter. In thousands of little ways like this, the wilderness becomes less wild. Our belief that we can "preserve" these lands may comfort us, but it is no less a delusion than that of the developers who believe they can draw boundless resources from them, for free, until the end of time.

It is always easy to lay blame, but the exercise is curiously unproductive. Workers blame environmentalists; environmen­talists blame developers; developers blame regulatory agen­cies; and regulatory agencies blame voters, whose ranks in­clude workers, environmentalists, and developers. The fingers point in a circle, and we are no wiser than when we began.

It is also easy to come up with alternatives. The use of fossil fuels, with all its attendant environmental costs, would clearly drop dramatically if we all switched to solar heat. Pollution could be slashed if wastes were recycled instead of discarded. More money would be available for improving the lot of the poor if the wealthy would forgo some profit. Unemployment would be reduced if corporate energy now wasted on meeting the increasingly arcane and complex demands of the regula­tory process could be used instead to create jobs. The prob­lem with these and similar solutions is not that they won't work; the problem is that no one is implementing them. Means of implementation have been suggested, but they remain untested. Everyone wants to live in Utopia, but no one wants to put out the energy necessary to get from here to there.

It is time to begin seriously rethinking the ways in which we approach these things.



The great English economist Alfred Marshall once compared supply and demand to a pair of scissors: one blade, he pointed out, was totally useless without the other. Exactly the same can be said of economics and ecology. The time has come when we must recognize that neither free enterprise in igno­rance of ecological principles, nor legalistic protectionism in ignorance of the laws of economics, is going to do more than temporarily improve our position on the planet. The time has come to look for the point where the scissors meetCthe point where we recognize the truths of both ecology and economics, the point where each action we take is tested and judged by its conformance to both of these sciences.

The Greek root oikos means "household"; nomos means "management." The word economics, derived from these roots, thus means literally "household management," and originally that is exactly what economics involved. Economists planned purchases, kept track of income and outgo, and generally made sure that household affairs ran smoothly. They still do that, but today household has taken on a considerably larger meaning. Ever since Adam Smith demonstrated that the behavior of individual households could not be considered apart from one another, but had to be seen in the much broader context of markets, the oikos of economics has been understood to mean not just a household enclosed by four walls, but the household that belongs to all of us. The plane­tary household: indeed, the planet itself.

The Greek root logos means "study." Ecology thus means literally "household study"; but, unlike economics, the word ecology was never meant to apply to a literal, four-walled household. The term was coined in the nineteenth century by natural scientists who were consciously basing their choice of roots on the newly expanded meaning of the older term. The "eco" in ecology has always referred to the planetary household.

Ecology and economics are often pictured as implacable foes. But there is only one household. Ultimately, if economics and ecology are both true, they cannot possibly conflict with one another.




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