Forests as Ecosystems

Eugene P. Odum

Some twenty-five years ago, I made an invited presentation at the annual convention of the Society of American Foresters entitled “The Life-Support Value of Forests,” which was published in the Proceedings of that meeting (1977). The first paragraph of that paper reads:

The time may soon come, if it is not already here, when a forest will be valued as much for its life-support capacity as for its yield of products and services. By life support, we are referring to the role of forests, along with other vegetated ecosystems, in maintaining the quality of air, water, and food along with other energy necessary for the human civilization to survive and prosper. It is not so much that we fail to recognize the value of vegetation in supporting vital life processes such as breathing, eating, and drinking because we certainly do in a vague, general sort of way. But in the past, we have not been able to satisfactorily quantify these values in competition with more materialistic ones. Thus, life support values of the forest ecosystem have too often ended up at the bottom of a list of “multiple uses” being considered (if they appear at all), even though common sense tells us that life support should rate among the very highest and best uses for forests.

After a brief review of what we knew then about forests as: (1) carbon sinks, (2) moderators of the downhill flow of water and sediments in the hydrological cycle, and (3) filters for air and water pollution, I discussed the “market failure” that occurs when the market economy fails to value the nonmarket goods and services of nature. I ended the article with this paragraph:

To get people to start thinking about Life Support values, we could suggest adding a phrase or so to the educational billboards that the U.S. Forest Service places at the entrances to or viewpoints within National Forests. The following is a copy of such a sign with added wording underlined:

UNDER FOREST SERVICE MANAGEMENT THIS FOREST PROVIDES LIFE SUPPORT FOR INDUSTRIAL AND URBAN AREAS WHILE AS A BONUS IT PRODUCES TIMBER, FORAGE, WILDLIFE, FISH AND ENERGY ON A SUSTAINED-YIELD BASIS FOR MAXIMUM PUBLIC BENEFIT. MULTIPLE USE MANAGEMENT IN ACTION!!

In retrospect, the time for serious consideration of nonmarket values had not yet come in the 1970s, but the time for such consideration is here today, as evidenced by the new ecological-economics society and journal, and the numerous papers and books by ecologist and economists that attempt to bridge the gap between market and nonmarket values. Also, it is noteworthy that, the U.S. Forest Service and other funding agencies are giving more support to biodiversity studies and forest management to include values other than the production of wood products.

Paralleling the increase of forest research and management, is ecology as a discipline, has emerged from its roots in biology to become a stand-alone discipline that interfaces organisms, the physical environment, and human affairs. This is in line with the root meaning of the word “ecology,” which is “study of the household” or the total environment in which we live. When one goes from the study of structure to the study of function, the physical sciences (including energetics, biochemical cycling, and earth sciences) have to be included. Now more than ever, we have to include humans and the social sciences, too.

Furthermore, the development of ecologically based pest management, as outlined in the National Research Council’s 1996 report, is a good example of expanding theory and management from dealing with each pest, one at a time, to more holistic approaches. Natural selection in undisturbed, diverse forests tends to promote coexistence in host parasite relationships, because if the parasite takes too much from the host, both may die. So, we can ask why are we having so much trouble with new pest diseases and exotics in intensely managed forests and agricultural crops.

In a commentary presented at a recent workshop on ecological based pest management, we listed the following four conditions or management practices that encourage pests (Odum and Barrett 2000). Although these factors referred to agriculture, they apply equally well to forestry, especially on plantations that are more crop than forests.

Eutrophication
Our effort to increase agricultural productivity worldwide in order to support the increasing numbers of people and domestic animals (which in turn excrete huge amounts of nutrients to the environment) has caused global eutrophication problems, which are perhaps the greatest threat to ecospheric diversity, resilience, and stability. Global warming that results from CO2 enrichment of the atmosphere is just one aspect of this overall perturbation. Nitrogen enrichment also is a serious threat (Henrikson et al. 1997; Vitousek et al. 1997). Excess nitrate fertilizer and other nutrient runoff favor many noxious weeds, exotic pests, and dangerous disease organisms because these organisms are highly adapted to high-nutrient environments.

The well-known red tide phenomenon is a good example of how enrichment can create a pest out of normally innocuous organisms. At their typical low densities, the red tide microorganisms in estuaries cause few or no problems. They secrete a toxin as a defensemechanism but not in concentrations that could affect fish. When the estuary is enriched by nutrient-filled pollution, however, the organisms can rapidly multiply and reach densities when their defensive toxins can cause massive fish kills.

Ecosystem Stress and Excesses
Humans tend not to be satisfied with a reasonably good yield and always seem to strive for more, even recognizing that it is possible to have “too much of a good thing.” When a crop plant or tree (or the cropland itself for that matter) is forced to produce a maximum possible yield of desired products (e.g., forced increase in the harvest ratio), the plant has very little energy left to defend itself from pests. This is one of the reasons we see an increase in pesticide use. Also, growers seeking the maximum rather than the optimum will often experience overshoot or “boom-and-bust” crop production patterns, as occurred with cotton in the Canete Valley of Peru in the 1950s (Barducci 1972) and in Texas in the 1960s (Adkisson et al. 1982).

Control Versus Eradication
A common response to the appearance of pest species is an effort to eliminate them completely rather than reducing their numbers to a point where their impact is small. The trouble with the “kill ‘em dead” approach is that it often involves heavy applications of pesticides, which can result in strong selection favoring resistant strains (the few individuals in a given pest population that have some mutation-derived differences in their metabolic pathways that confer resistance against the pesticide). More moderate measures that control but do not eliminate pest species appear to alter the relative frequency of these resistant mutations and slow the development of resistance in the pest populations. An example is the development of a rust-resistant strain of wheat, which is accomplished by introducing a “slow rust” gene that keeps the disease at a low level so that there is less selection pressure on the rust fungus to mutate (Holden 1992). Therefore, reducing the overuse of a pesticide may help reduce the development of particularly challenging resistant pests.

Monoculture Vulnerability to Pest Invasion
For decades, the goal of agriculture and agroforestry has been to increase crop yields per unit of land by promoting industrial culture that involves large-scale monocultures, the use of fossil-fuel-powered machinery, and very heavy applications of chemical subsidies. One result, as documented in numerous papers, reports, and books, is the rapid increase and spread of pests (see two reports: NR 1989, and 1996; and two agroecology books: Altieri 1987; Gliessman 1998).

Fortunately, new practices involving crop rotations, strip cropping, trap crop buffers, and other diversifications that are coming into greater use do reduce pests and decrease the need for heavy pesticide use.

Adkisson, P.L., G.A. Niles, J.K. Walker, L.S. Bird, and H.B. Scott. 1982. Controlling Cotton Insects Pests: A New System. Science 216:19-22.

Altieri, M.A. 1987. Agroecology: The Scientific Basis of Alternative Agriculture. Boulder, CO: Westview Press.

Barducci, T.B. 1972. Ecological consequences of pesticide used for the control of cotton insects in Canete Valley, Peru. Pp. 432-438 in The Careless Technology, M.T. Farvar and J.T. Milton, eds. Garden City, NY: Natural History Press.

Gliessman, S.R. 1998. Agroecology: Ecological Processes in Sustainable Agriculture. Chelsea, MI: Ann Arbor Press.

Henrickson, A., Hessen, D. O., and Kessler, E., eds. 1977.  Nitrogen: A Present and a Future Threat to the Environment. Ambio. 26:253-325.

Holden, C. 1992.  Hard-won victory over wheat blight.  Science 258:551.

National Research Council. 1996. Ecologically Based Pest Management: New Solutions for a New Century. Washington, D.C.: National Academy Press.

Odum, E.P, and G. Barrett. 2000. Pest Management: An Overview. Nat. Res. Council. National Academy Press. P. 1-5.

Vitousek, P. M., Aber, J., Howarth, R. W., Likens, G. E., Matson, P. A., Schlindler, D. W., Schlesinger, W. H., Tilman, J. D. 1997.  Human Alteration of the Global Nitrogen Cycle: Causes and Consequences.  Issues in Ecology, Report 1. Ecological Society of America. Washington, D. C.

NOTE: The watercolor illustrations in this paper are by Martha Odum.  Images are reproduced courtesy of Dr. Eugene P. Odum.