Agricultural Ecosystems and Agricultural Ecology

Ecosystem as Landscape Building Block

The term "ecosystem" was first proposed by Tansley (1935) as a name for the interaction system comprising living things together with their nonliving habitat. He regarded the ecosystem as not only the organism complex, but also the whole complex of physical factors forming what we call the environment. It was first applied to levels of biological organization represented by unites such as community and the biome. Odom (1952) and Evans (1956) expanded the extent of the concept to include other levels of organization.

An Agroecosystem Model

What are the basic components of agroecosystems? Just as natural ecosystems they can be thought of as including the processes of primary production, consumption, and decomposition interacting with abiotic environmental components and resulting in energy flow and nutrient cycling. Economic, social, and environmental factors must be added to this primary concept because of the human element that is so closely involved with agroecosystem creation and maintenance.

Agroecosystem Characteristics

Agricultural ecosystems (referred to as agroecosystems) have been described by Odum (1984) as domesticated ecosystems. He states that they are in many ways intermediate between natural ecosystems (such as grasslands and forests) and fabricated ecosystems (cities).

Agroecosystems are solar powered (as are natural systems) but differ from natural systems in that:

there are auxiliary energy sources that are used to enhance productivity; these sources are processed fuels along with animal and human labor;
species diversity is reduced by human management in order to maximize yield of specific foodstuffs (plant or animal);
dominant plant and animal species are under artificial rather than natural selection; and,
control is external and goal-oriented rather than internal via subsystem feedback as in natural ecosystems.

Agroecosystems do not happen without human intervention in the landscape. Therefore, creation of these ecosystems (and maintenance of them as well) is necessarily concerned with the (human) economic goals of production, productivity, and conservation. Agroecosystems are controlled, by definition, by management of ecological processes.

Crossley, et al, (1984) addressed the possible use of agroecosystem as a unifying and in many ways clarifying concept for proper management of managed landscape units. All ecosystems are open, that is, they exchange biotic and abiotic elements with other ecosystems. Agroecosystems are extremely open — with major exports of primary and secondary production (plant and animal production) as well as increased opportunity for loss of nutrient elements. Because modern agroecosystems are entirely dependent on human intervention, they would not persist but for that intervention. It is for this reason that they are sometimes referred to as artificial systems as opposed to natural systems that do not require intervention to persist through space and time.

Definitions of agroecosystems often include the entire support base of energy and material subsidies, seeds, and chemicals, and even a sociopolitico-economic matrix in which management decisions are made. Crossley (1984) stated that while this is logical, he preferred to designate the individual field as the agroecosystem because it is consistent with designating an individual forest catchment or lake as an ecosystem. He envisions the farm system as consisting of a set of agroecosystems — field with similar or different crops — together with support mechanisms and socioeconomic factors contributing to their management.

Agroecosystems retain most if not all the functional properties of natural ecosystems — nutrient conservation mechanisms, energy storage and use patterns, and regulation of biotic diversity.

Ecosystem Pattern and Process

Throughout the United States the landscape consists of patches of natural ecosystems scattered (or imbedded) in a matrix of different agroecosystems and fabricated ecosystems. In fact, about three-quarters of the land area of the United States (USDA, 1982) is occupied by agroecosystems.

The pattern created by this interspersion incorporates elements of the variability of structure and separation of functions among the various ecosystems. Pattern variables quantify the structure and relationships between systems; process implies functional relationships between and within the biotic and abiotic ecosystem components. Within agroecosystems processes include:

enhanced productivity of producers through fertilization
improved productivity through selective breeding
management of pests with various control methods
management of various aspects of the hydrologic cycle
landforming

Agricultural Ecology

Simply stated, agricultural ecology is the study of agricultural ecosystems and their components as they function within themselves and in the context of the landscapes that contain them. Application of this knowledge can lead to development of more sustainable agricultural ecosystems in harmony with their larger ecosystem and ecoregion.

Literature

Crossley, D.A. Jr., G.J. House, R.M. Snider, R.J. Snider, and B.R. Stinner. 1984. The positive interactions in agroecosystems, In: Agricultural Ecosystems, R.Lowrance, B.R. Stinner, and G.J. House, Eds. John Wiley & Sons, New York. pages 73-81.

Evans, Francis C. 1956. Ecosystem as the basic unit in ecology. Science 23:1127-1128.

Odum, Eugene P. 1952. Fundamentals of ecology, 1st edition. W.B. Saunders Co., Philadelphia.

Odum, Eugene P. 1984. Properties of agroecosystems, In: Agricultural Ecosystems; R. Lowrance, B.R. Stinner, and G.J. House, Eds. John Wiley & Sons, New York. pages 8-11.

U.S. Department of Agriculture (USDA). 1982. Agricultural Statistics 1982. U.S. Government Printing Office, Washington, D.C.

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