Agricultural Ecology

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The origins of agriculture can be traced back to Mesopotamia, whence it spread to the fertile crescent of southwestern Asia. In Africa, ancient climatic changes forced humans to make adaptations in their way of life. About 10,000 years ago, as drought and desertification spread from the north into central Africa, nomadic hunter-gatherers began to settle and live by fishing and planting the seeds culled from wild grains in the wet ground left behind by seasonally receding lakes. In the boundary zone between northern and central Africa, planters refined stone tools for digging and hoeing and selected those plant varieties that were most easily domesticated. Around 5000 B.C.E., a cultivated root crop, the white Guinea yam (Dioscorea rotundata), became the new staple food. In the northern savanna, wild millet and sorghum seeds were introduced by cereal farmers. The African agricultural revolution continued with increases in the scale of production and improvements in the food crops themselves. Nutritious oils processed from trees such as the oil palm (Elaeis guineensis) were an important addition to the human diet.

The resulting improvements in human health led to population growth, territorial expansion and new cultivation. Indonesian migrants settling in Madagascar, probably during the first millennium C.E., introduced bananas (Musaceae) and other new foods that were widely adopted in continental Africa. Like the indigenous yam tubers, bananas were propagated not by seeds but by roots and cuttings. The new staples thrived in eastern Africa, where more banana varieties were developed than in any other part of the world. In Egypt the keeping of livestock imported from the fertile crescent of southwestern Asia led to the cultivation of cereal grains such as barley, sorghum, and flax by about 5000 B.C.E. Farming in the Nile River valley made possible population growth and more complex social organization. By 2500 B.C.E., an Egyptian system was in place of overlords and land tenants working irrigated fields and orchards growing vegetables, fruits, and grains with the help of beasts of burden and improved sickles. This became the model for agriculture in the modern sense of the term.

During the era of European imperialism, colonial economic systems dependent on corvee labor in the tropics replaced small-scale local farming with large plantations and monocropping for export. France tapped rubber in southeast Asia, England planted tea in Ceylon, and the United States raised sugar cane in Hawaii. In the colonial world, much traditional subsistence farming was replaced by commercial operations that took advantage of cheap labor and abundant resources while returning little of value to indigenous laborers. The industrial revolution created a huge demand for labor and the resources on which production was based. Mid-nineteenth century textile mills in England were dependent on cotton imported from the slave labor plantations of the southern United States. Some of the most violent and turbulent upheavals of twentieth-century social movements found their popular base in land reform programs that targeted the structural inequities of colonial systems.

Traditional swidden (slash and burn) methods of shifting cultivation in the tropics allowed soils to be replenished by lying fallow for a period of years after cyclical harvesting of rotated crops. Although these time-tested methods have usually been thought to minimize biodiversity, evidence shows that shifting cultivators also preserves wild species as additional resources when economic opportunity permits. Asian forests are mostly old growth that had been cleared in earlier times, by human activity or natural causes, and reached a state of equilibrium. Swidden tracts left to go wild also support significant animal life. In the early postcolonial era, after World War II, international efforts to alleviate chronic poverty and meet the growing food demands of an exploding world population led to attempts at modernizing and rationalizing Third World agricultural production through experimentation with high-yield seed varieties bred in laboratories and new farming techniques. The Green Revolution of the1960s, which introduced genetic monocrops in proprietary seedless variants, produced spectacular short-term results but ultimately did more harm than good. The new methods both failed to produce sustainable harvests and, in the long run, depleted both soil fertility and available seed stock. As a result, once-fertile lands were left barren, and farmers were unable to replenish their crops by the traditional means of saving seeds culled from previous annual harvests. In the biotech farming of today, intellectual property issues are coming to the fore as the adoption of patented super-seed varieties enhances the structural dependency of Third World farmers and accentuates the need for agricultural reform. In technologically advanced farming of specialized high-yield varieties, as practiced by commercial agribusiness interests in the United States and Australia, maintenance of crop diversity helps in the cross-pollination of plants, the control of pests, and the decomposition of organic matter in the soil.

The existing diversity of crops worldwide, selected over 10,000 years of domestication and cultivation, is rapidly diminishing. In North America native farmers first grew Mesoamer-ican varieties of maize, beans, and squash; in the era of colonization they switched to domesticated European plants. Today the breadbasket of the North American plains is the most productive agricultural land in the world, providing food for millions. Nevertheless, market-driven tendencies toward reliance on massive plantations of single varieties—such as the golden russet potato, favored by fast-food outlets for french fries because of its uniform appearance—reduce the gene pool and leave crops with a dangerous lack of resistance to blight. The value and utility of extinct crops can be inferred from the fact that they were once raised domestically. Their surviving progenitors in the wild might be adaptable to increase the genetic diversity and long-term viability of domestic varieties.

European agriculture is relatively low in biodiversity. Over the past millennium, the variety of species in western and central Europe has declined, probably because of the self-contained character of farms. A wide range of crop species were introduced between the eighteenth and twentieth centuries, along with the adoption of technological advances originating in Britain and the lowland countries of western Europe. More recently, increased mechanization has combined with rising costs and falling prices, driving European farmers to seek increased efficiency and higher yields by specializing in a select few crops. According to the UN's Food and Agriculture Organization, rural livelihoods are rapidly changing, becoming far less dependent upon agriculture than is commonly supposed. In Africa south of the Sahara, farming accounts for between 50 and 70 percent of income, while in the southern part of the continent that figure is as low as 10 to 20 percent. Biodiversity of food sources remains relatively high in sub-Saharan Africa, with 60 wild grass species used for food. In Botswana, the agropastoral Tswana people obtain food from 126 plant species and 100 animal species. The maintenance of a wide variety of crops can ensure a steady if modest food supply that is reliable and resistant to the vagaries of climate change. In southern Africa, gradual mixed plantings of endemic species are proving more successful at weathering drought and erratic rainfall than many imported seeds planted according to the calendar.

The developing field known as agroecology takes a systemic ecological approach to the analysis of farming. Its practical application is to promote minimization of energy input and maximization of useful output, while avoiding the negative effects of pollution and depletion of resources. New ecological studies suggest that African rangelands are less stable, less prone to inevitable desertification, and more resilient than previously believed. Local ethnographic knowledge supports the observation that these ecosystems are subject to sudden drastic and unpredictable environmental swings in aridity, erosion, and carrying capacity, rather than slow decline. Human engineering has transformed deserts into irrigated gardens (as in Israel), developed rural agriculture through electrification (as in Egypt's Nile River valley), and dramatically modified soil fertility, the nutritional value of crops, and the gene pool of seeds.

In the Green Revolution, so-called miracle rice produced temporarily high yields, but the high amount of nutrients needed to grow it placed an untenable strain on the soil. The lack of available seed made the damage incalculably more severe. On the Indonesian island of Bali, farm lands could no longer reliably produce the sustainable harvests grown for many generations on terraced rice fields. Outside agronomists did not have a clear understanding of how the calendar of the Hindu ritual cycle, controlled by the priests of the Bali-nese water temples, regulated the flow of irrigation and the agricultural cycle. The religious ceremonial not only is a symbolic representation of social cooperation but also controls the timing of planting and harvesting in phase with the seasonal climatic rounds. The separation of religion and ecology, in this case, was a Western mode of conceptualization whose imposition caused material harm to the ecology of Bali and the livelihood of the Balinese. Anthropologists and other researchers were able to mediate this conflict between the guardians of traditional culture on the one hand and officials responsible for development on the other, furthering the goals of productivity and modernization as well as the continuation of customary religion and social organization. Cost-benefit analyses must take local patterns, social organization, and cultural values into account before drastic change is instituted. By not rushing to devalue and abandon traditional agricultural systems before understanding their integrative ecological functions, a balanced biocultural ecosystem was maintained in Bali.

Present efforts sponsored by the UN Food and Agricultural Organization to sustain crop biodiversity have the goal of attaining food security, defined as universal availability, stability, and access. By that standard, more than 800 million people today are food insecure. Land use and land cover analyses are the first steps to the integrated management of environmental, economic, and social functions. By combining local wisdom and resources with scientific techniques and international aid to encourage the preservation and cultivation of agricultural biodiversity, societies in the future should be able to reap the benefits of sustainable farming practices.

See also: Agriculture and Biodiversity Loss: Industrial Agriculture; Agriculture and Biodiversity Loss: Genetic Engineering and the Second Agricultural Revolution; Agriculture, Origin of; Agriculture: Benefits of Biodiversity to; Alien Species; Biogeography; Coloniality; Conservation Biology; Cultural Survival, Revival, and Preservation; Dams; Deserts and Semiarid Scrublands; Economics; Ethnoscience; Food Webs and Food Pyramids; Industrial Revolution/ Industrialization; Land Use; Organizations in Biodiversity, The Role of; Population, Human, Curbs to Growth; Sustainable Development


Kühbauch, Walter. 1998. "Loss of Biodiversity in European Agriculture during the Twentieth Century." In Biodiversity: A Challenge for Development Research and Policy, edited by W. Barthlott and M.

Winiger, pp. 145-155. Berlin, NY: Springer; Lansing, J. Stephen. 1987. "Balinese Water Temples and the Management of Irrigation." American Anthropologist 89: 326-341; Minnis, Paul E., and Wayne J. Elisens, eds. 2000. Biodiversity and Native America. Norman: University of Oklahoma Press; Shiva, Vandana, et al. 1991. Biodiversity: Social and Ecological Perspectives. London: Zed; UN Food and Agriculture Organization. 1999. "Sustaining Agricultural Biodiversity and Agro-Ecosystem Functions." Prepared by Wino Aarnink et al. Rome: UN-FAO; Warren, D. Michael, L. Jan Slikkerveer, and David Brokensha. 1995. The Cultural Dimension of Development: Indigenous Knowledge Systems. London: Intermediate Technology.

Agriculture and Biodiversity Loss: Genetic Engineering and the Second Agricultural Revolution

Genetic engineering has many and varied effects on biodiversity, but its likely long-term result will be a decrease in genetic variability of crops and other species. In a narrow sense, the large-scale deployment of genetically engineered crops that began in the mid-1990s has increased the genetic diversity of target crops by introducing wholly novel DNA segments (transgenes). When successfully introduced from another species, a transgene causes a plant to express a new trait, with little or no change in diversity among the 10,000 to 100,000 other genes native to the species. Probably more significant than the direct effect of gene insertion, however, are the indirect effects of transgenes on the biodiversity of the target crop, other crops, and other life forms. Hard data are scarce, and the direction and magnitude of biotechnology's effect on biodiversity will be evaluated accurately only after transgenes have been deployed for decades. The eventual consequences will depend on the biotechnological techniques

Genetically engineered corn plants grow in controlled conditions at the SunGene Technologies laboratory, Palo Alto, California. (Lowell Georgia/Corbis)

employed, the genes selected for manipulation, and the ways in which transgenic crops are used. Nevertheless, when viewed as an extension of industrial agriculture, genetic engineering is likely to accelerate homogeniza-tion of the biosphere.

The explicit goals of biotechnology, like those of traditional plant breeding, are to increase agricultural productivity and profitability, and often to improve human nutrition. The consequences for biodiversity are largely unplanned and indirect. Although some predictions can be made, virtually all results of research on biotechnology's environmental impact are hotly debated among scientists.

Early research suggested ways in which transgenes could expand the diversity of crops and associated species. By increasing productivity on land already under cultivation, transgenic crops could forestall expansion of agriculture and the displacement of more diverse natural vegetation. Introduced genes for pest resistance have augmented the collections of naturally occurring genes available to plant breeders, giving them more options in developing sustainable resistance. Genetic resistance, in turn, may reduce the use of broad-spectrum pesticides and the consequent loss of diversity in nontarget species. Engineering of minor crop species to produce economically valuable enzymes, vaccines, or hormones could allow farmers to diversify the range of crops they grow. Manipulation of genes that control chromosome pairing or other aspects of meiosis could allow breeders to produce fertile hybrids between previously incompatible species.

These potential contributions likely will be canceled out in the long term by genetic engineering's negative effects on biodiversity. Historically, a phenomenon known as genetic erosion has occurred when crop varieties with high yields or other traits desired by farmers have displaced more genetically diverse traditional varieties. Transgenic technology is the latest in a long line of genetic tools developed over the past century, and it will enhance the power of modern plant breeding to cause genetic erosion. In the United States, seed of nontrans-genic maize, soybean, and cotton, for example, is now less available because of the wide adoption of transgenic hybrids and varieties.

Diversion of research funds from traditional plant breeding into genetic engineering can further restrict the genetic diversity of farmers' seed sources. Development of a transgenic variety can cost more than twenty times as much as the breeding of a variety through the traditional route of hybridization and selection. Given such a ratio, a breeding program could release to farmers either five transgenic varieties or 100 nontransgenics for an equivalent investment. Whatever their agronomic performance, the 100 varieties are almost certain to encompass more genetic diversity than the five transgenics.

Transgenes may cause ecological disruption and loss of biodiversity that goes well beyond genetic erosion in the farmer's field, however. Some evidence for this comes from the first transgenes to be deployed over large areas of cropland—a gene for resistance to the herbicide glyphosate in soybean and one coding for the Bt toxin that confers insect resistance in maize and cotton. Spraying a field with glyphosate eliminates virtually every plant of every species, except for engineered crop plants carrying the resistance gene. Eval uating the consequences for local or regional biodiversity will require many years, but some computer models have predicted reduction of plant and animal populations. Transgenic maize or cotton plants that produce the Bt toxin in all plant tissues at all stages of growth can dramatically reduce local populations of toxin-susceptible insects. Research has demonstrated toxicity to parasites and predators that attack insects feeding on Bt crops. Concern is compounded by reports that the toxin persists well after harvest, bound to soil particles where it could alter populations of soil microorganisms. However, despite such studies, the long-term effect of Bt on diversity is unknown. Some loss might be avoided by engineering Bt genes to produce the toxin only when the plant is being attacked and only in the tissue being eaten by the insect.

There is widespread evidence of gene flow through natural cross-pollination between crops and related weed or wild species, and transgenes will be transferred in the same way. There is no consensus, however, on what that will mean for biodiversity. In one catastrophic scenario, an escaped transgene might allow a wild or weed species to increase its density and range greatly, displacing other species. Evolutionary theory suggests that a randomly introduced gene has a higher probability of reducing than of increasing a weed's fitness, but whatever the average effect of a particular gene on fitness, we cannot rule out the possibility that a "superweed" may emerge once many different species are exposed to transgenes in many different ecosystems.

Monocultures lack the inherent protection against fungi, bacteria, viruses, arthropods, and weeds that comes with the genetic variability of natural ecosystems or some traditional farming practices. Genetically uniform crops must be protected against pests, and that is most often accomplished through incor poration of resistance genes through breeding, or by the use of chemical control. As illustrated by the transgenes for glyphosate resistance and the Bt toxin, biotechnology is an enhanced method for applying these same control strategies. Therefore its successful application can permit farmers to continue sowing monocultures, instead of turning to pest-control methods that employ genetic diversity, such as variety blends, polycultures, or crop rotation.

—Thomas S. Cox and Wes Jackson

See also: Agriculture and Biodiversity Loss: Industrial Agriculture; Agriculture: Benefits of Biodiversity to


Butler, Declan, and Tony Reichhardt. 1999. "Assessing the Threat to Biodiversity on the Farm." Nature 398: 654-656; Hilbeck, Angelika. 2001. "Implications of Transgenic, Insecticidal Plants for Insect and Plant Biodiversity." Perspectives in Plant Ecology, Evolution and Systematics 4: 43-61; Holdrege, Craig. 1996. Genetics and the Manipulation of Life: The Forgotten Factor of Context. Herndon, VA: Lindisfarne; Rissler, Jane, and Margaret Mellon. 1996. The Ecological Risks of Engineered Crops. Cambridge, MA: MIT Press.

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