The Strategy of Ecosystem Development: An understanding of ecological succession provides a basis for resolving man’s conflict with nature. – E.P. Odum (1969)

In this article, Odum suggests the application of successional theory to ecological system studies in order to better understand the development of ecosystems. According to the author, until this article was written in 1969, the majority of the understanding of the how ecosystems developed relied upon descriptive data and “highly theoretical assumptions” with very little attempt to experimentally test hypotheses. Odum identifies the lack of experimental work in ecosystem ecology is the misinterpretation of the definition of succession. Stressing the idea that succession consists of a complex interaction of processes. In applying a successional model to ecosystem studies, he uses a tabular model to outline “components and stages of development at the ecosystem level as a means of emphasizing those aspects of ecological succession that can be accepted on the basis of present knowledge, those that require more study, and those that have special relevance to human ecology” (596[262]).

Definition of Succession

Odum defines succession according to three parameters:

(1)     It is an orderly process of community development that is reasonably directional and, therefore predictable.

(2)     It results from modification of the physical environment by the community; that is, succession is community-controlled even though the physical environment determines the pattern, the rate of change, and often sets limits as to how far development can go.

(3)     It culminates in a stabilized ecosystem in which maximum biomass (or high information content) and symbiotic function between organisms are maintained per unit of available energy.

(596[262])

In Table 1, Odum outlines 24 attributes of ecological systems grouped into six major structural and functional characteristics of ecosystems.

Bioenergetics of Ecosystem Development

Bioenergetics of the ecosystem are defined by attributes 1-5 of Table 1. These attributes refer to changes within the ecosystem itself. The theory in this is that as the ratio (P/R) of the rate of primary production or total (gross) photosynthesis (P) and the rate of community respiration (R) approaches 1, succession occurs. “energy fixed tends to be balanced by the energy cost of maintenance…in the mature or ‘climax’ ecosystem’ (597[263]).

Components of Succession in a Laboratory Microcosm and a Forest

Odum then discusses the above bioenergetics theory using laboratory aquatic microsystems from ponds cultured by Beyers (1963[6]). During the initial stages of the experiment, “the daytime production (P) exceeds nighttime respiration (R), so that biomass (B) accumulates in the system” (597[263]). After the initial bloom, both rates decline eventually becoming nearly equal with the B/P ratio increasing as the microenvironment approaches steady state.

Although Table 1 refers to changes brought by biological processes within the ecosystem, Odum also stresses the importance of outside influence on Eutrophication. In the case of lakes, nutrients are imported to the lake from the watershed. Thus, he concludes that more oligotrophic conditions can be restored by slowing of nutrient input. This, in turn, can be used to deal with water pollution problems. However, this can only be achieved through functional studies of the larger landscape.

Food Chains and Food Webs

Changes in the food chains also occur as ecosystems develop. Low diversity in the early stages of ecosystem development maintain a simple and linear food chain. As the system matures, the chains become more and more complex creating food webs. Within these webs, the Odum found that the majority of biological energy flow follows a detritus pathway (598[264]).

Diversity and Succession

Within Table 1 (items 8-11), Odum lists four components of diversity: (8) species diversity – variety component; (9) species diversity – equability component; (10) biochemical diversity; and (11) stratification and spatial heterogeneity (pattern diversity). These kinds of diversity are suggested by the author to follow different developmental avenues that lead to stability of the system. According to the author, the diversity-stability relationship needs better understood. Is diversity necessary for the stability of the ecosystem?

Nutrient Cycling

As a system matures, its capacity to entrap nutrients becomes greater (599[265]). In this discussion, Odum cites Bormann and Likens (1967[24]) and questions whether or not the increased water yield of the stream is a good thing. He suggests that reducing the vegetation around the stream would be accompanied by a greater loss of nutrients, and thus affect those systems downstream. However, the nutrient retention of the biomass at this point (1969) still needs to be tested.

Selection Pressure: Quantity versus Quality

Citing MacArther and Wilson (1967[26]), Odum suggests that species with high rates of reproduction and growth are more likely to survive in uncrowded situations earlier in ecosystem development, while competitive species with low growth would fare better in a more diverse environment in the later stages of the system. Understanding the implications of the dynamics of populations could have potential implications for the adaptations that will occur with overcrowding that is occurring with human populations.

Overall Homeostasis

The review of ecosystems outlined by Odum was in an attempt to discuss the complex nature of the processes that interact with the system (600[266]). Understanding how the entirety of the system as a whole contributes to a better grasp on the nature of ecosystems. This leads to the question of how these systems age: as they get older do they return to a state of “vulnerability”?

Relevance of Ecosystem Development Theory to Human Ecology

Figure 1 is an interpretation of the human view of nature. According to Odum, humans look at the landscape and look for ways to achieve high production of the biomass and fail to see it as a limited resource. In other words, humans see a high P/B efficiency when in reality an ecosystem has a high B/P efficiency.

According to Odum, the human preoccupation with production has caused them to forget that the landscape is not merely a “supply depot” but a home where humans and other organisms must live (600[266]). In other words, are humans getting “too much of a good thing” when they focus on only one aspect of the landscape rather than the impacts on the environment as a whole.

Pulse Stability

There are cases when recurring changes in the ecosystem result in that system to remain in some intermediate stage between development and maturity. This is known as pulse stability. Organisms in the everglades, for example, have adapted to fluctuating periods wet (flooded) and dry periods. In this system wood storks only breed when water levels are falling but will not nest when conditions are still wet. A situation such as this only works in a system if the community is complete. Any sudden change (such as those caused by people) results in the inability of the ecosystem to adapt and reach any point of stability.

Prospects for a Detritus Agriculture

Natural conditions are also better for growing food. Current agricultural practices of selection of plants for rapid growth and edibility make them vulnerable for attacks by insects (602[268]). This, in turn, results in the use of harmful pesticides. Odum suggests that reversing the strategy and selecting plants that have adapted their own insecticides from using delayed consumption of detritus would result in a much clean and stable environment. This would also result in the utilization of natural systems rather than modification and destruction.

The Compartment Model

Odum concludes that a compartmentalization strategy of systems needs to be utilized so that “growth type, steady state, and intermediate-type ecosystems can be linked with urban and industrial areas for mutual benefit” (602[268]). While this would require laws governing zoning procedures, it would limit the impact of humans on the environment. If nothing else, it would provide the opportunity for an increased study and awareness of how much people depend on the environment.