One of the greatest threats to natural biodiversity arises from the growing imbalance between human populations and the availability of food, which is especially acute in many of the world's least prosperous nations. Food scarcity lies behind the encroachment of extensive slash-and-burn agriculture upon natural tropical forests, a major cause of biodiversity loss. How can the needs of poor, hungry people be reconciled with the laudable goal of preserving natural biodiversity? To find a solution, we will have to devise effective strategies of sustainable development; these are policies and programs that not only stimulate progressive economic growth but also are socially and environmentally sustainable. The UN World Commission on Environment and Development has defined sustainable development as "development that meets the needs of the present without compromising the ability of future generations to meet their own needs" (WCED, 1987, p. 43).
Designing and implementing sustainable development strategies will be neither quick nor easy. For example, while it seems obvious that reducing human population growth should be a high priority, birth control programs will not succeed on the global level without fundamental reforms in education, health care, and the status of women; such reforms, unfortunately, will probably take many years. A more promising, though more complex, approach is to seek environmentally and socially sustainable ways of increasing food production while simultaneously applying the brakes to human population growth.
One potentially sustainable strategy for enhancing food production involves agricultural intensification, the purpose of which is to increase agricultural yields without expanding the overall area under cultivation. What forms of agricultural intensification might be most effective in less-developed nations? Although it is true that agricultural yields can be increased through "green revolution" programs (usually involving high-yielding crop strains, mechanization, chemical fertilizers, and pesticides), researchers have found that such approaches are costly and tend to favor wealthy farmers over poorer ones, giving the latter no choice but to pursue the more extensive kinds of cultivation that are so damaging to natural biodiversity. Canal irrigation and other water management techniques are forms of agricultural intensification that tend to be more widely available. Yet such methods can enhance food production over the long term only if water is employed efficiently, with maximal benefit to crops and with minimal waste.
Researchers have found that water-use efficiency is often hindered by bureaucratic incompetence, water-access disputes, wasteful applications, and, increasingly, human-induced climate changes that are altering the global distribution of water. Among the likely effects of global warming will be a climatic regime in which some areas receive far less rain and others far more than is currently the case. Future water management projects will have to be flexible enough to deal with such climatic perturbations, along with an array of political and technological challenges. One outstanding question in this regard is whether small-scale strategies, low in cost and tailored to local conditions, might actually be more sustainable over the long run than large-scale projects run by centralized bureaucracies. Of course, such a question cannot really be answered without long-term information on the successes and failures of various kinds of agricultural systems. Archaeology is one field that is especially qualified to provide such long-term data on strategies of water management and agricultural intensification in other times and places. Let us look at some examples.
In Mexico and Venezuela, archaeologists have studied the remains of small-scale agricultural systems that, in pre-Hispanic times, actually sustained larger human populations than do the modern systems now in use in those same localities (Spencer 2000). One example involves human settlements associated with the Purrón Dam, an ancient dam and irrigation system in the Arroyo Lencho Diego locality of the Tehuacán Valley, Mexico. Only 260 people lived at San Rafael in the Lencho Diego region in 1990, sustained by water from a long and costly irrigation canal built by the federal government to transport water from a distant source. By contrast, the ancient agricultural system used water from the local arroyo and yet managed to support a population of 975 to 1,190 (based on the number of archaeological households) during the Early Palo Blanco phase (150 B.C.E.-250 C.E.). A second case is the archaeological site of La Coyotera, near Santiago Dominguillo in the Cañada de Cuicatlán, Mexico; this site is also associated with a pre-Hispanic irrigation system. In 1990 the Dominguillo locality had a population of 477, but one thousand years ago some 1,345 to 1,675 people were sustained by irrigation agriculture there, even though the ancient system was less centralized and much smaller in scale than the irrigation systems recently built by the federal government. A third example is from the western Venezuelan state of Barinas, where archaeologists have surveyed and excavated the La Tigra drained-field agricultural site, in the alluvial zone of the Gavan Locality. The drained-field technique involved the digging of multiple canals, and it required a moderate investment of labor; yet it allowed for the cultivation of two crops per year (instead of just one). The canals served to collect scarce rainwater at the onset of the rainy season, and they also promoted proper drainage in the alluvial zone during the peak of the rainy season; the result was a lengthening of the growing season and a doubling of productive output. At present the economy of the Gavan Locality is oriented toward large-scale ranching, and the area is home to hundreds of cattle but only some fifty people. Yet during the Late Gavan phase (550-1000 C.E.) the human population here totaled between 925 and 1,375, supported in part by the drained-field system.
These cases suggest that archaeological data on traditional agricultural systems could be put to good use by contemporary planners who are trying to find low-cost, sustainable ways to increase agricultural production in tropical countries. These three systems were all relatively small in scale; they required only modest amounts of local labor for their initial construction and drew strictly upon local sources for their water supply. The operation of these systems did not cause any detectable biodiversity loss in their natural settings. Nor is there evidence that an elaborate bureaucracy was required to build or manage any of them. Yet they worked well for hundreds of years, and their success provides support for the argument that small-scale, local solutions are potentially more sustainable than large-scale, centralized strategies of agricultural intensification (see Mabry 1996).
From archaeology we can learn which strategies have worked in the past, under what conditions, and for how long. We can draw upon such data as we try to plan wisely for what lies ahead.
—Charles S. Spencer
See also: Agriculture and Biodiversity Loss: Industrial Agriculture; Population Growth, Human; Subsistence; Sustainable Development
Mabry, Jonathan B., ed. 1996. Canals and Communities: Small-Scale Irrigation Systems. Tucson: University of Arizona Press; Spencer, Charles S. 2000. "Prehis-panic Water Management and Agricultural Intensifications in Mexico and Venezuela: Implications for Contemporary Ecological Planning." In Imperfect Balance: Landscape Transformations in the Precolumbian Americas, edited by David Lentz, pp. 147-178. New York: Columbia University Press; WCED (World Commission on Environment and Development). 1987. Our Common Future. Oxford: Oxford University Press.
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