The environmental impact of rising populations throughout the world using increasing amounts of both net and per capita resources demands consideration. Increasing consumption will have complex global and local consequences that will affect the developing world the worst (Revkin). Economic development will provide the greatest protection to any individual developing nation (Schelling 3). How developing nations handle their environment and growth will affect the entire world. The destruction of the rainforests located in many developing nations will contribute unmanageable amounts of carbon to global warming. As resource demands increase along with population and economic growth, people push against the stability and ecosystem function of these rainforests in order to harvest resources. The demands placed on communities within such nations make traditional methods of livelihood and sustainability impractical. Overpopulation and economic pressures cause communities that have relied on swidden agriculture to use slash-and-burn agriculture, increasing global deforestation and global warming.

The structure of swiddens make them sustainable but also limit their use for supporting the growth of cities. Swiddens, usually 0.4-0.6 hectares (Dufour 653), are diverse multi-level agricultural plots (Dufour 652). They occur in almost all areas with tropical rainforests, including Southeast Asia, the Philippines, West Africa and South America (Fox 521). Native peoples cut swiddens out of sections of rainforests, sometimes using burning techniques, and cultivate the plots for a number of years and then allow the plots fallow. Families usually manage several swiddens of different ages to gain access to different types of crops (Dufour 654), though specific usage varies between tribes (Miller 157-158). Per unit of cultivated area, during periods of cultivation, swiddens often produce yields over double those of continuous-use fields (Dumond 302). Swiddens, however, require long fallow periods and must exist in relatively isolated sections of forests; they cannot produce much excess food to support cities.

The system works ecological by using diversity to enhance ecosystem function and allowing adequate regeneration time. Rainforests store most of their nutrients in the trees and other plants (Miller 151). Farmers can burn the plants to release the nutrients but because the renewal rate is slow the plots become barren after a few years. The high amounts of diversity present occur because of the amount of heat, light, rain and limited nutrient resources. Species evolve to be highly specialized, competing effectively to obtain different nutrients (Loreau 806). The swidden system suits this ecosystem well because it uses the same mechanisms to harvest the forest as the forest does to regenerate itself. Specifically, it uses small-scale disturbances to free resources and then reallocates them diversely, allowing for adequate recovery time. Managing succession of plants through rotation and diversity gives the agriculture system its renowned stability in the difficult environment of the rainforests (Fox 522).

The historical relationship between swiddens and civilization suggest that the two hold a tenuous coexistence. The most important success story of swidden agriculture comes from the Mayan empire. Some archeologists believe that the shifting of lands and long fallow times required in swidden agriculture caused the spread of villages and supported the empire. The expansionist modification on swidden agriculture, which was not entirely sustainable, depended on new resources and peace among the villages (wars would quickly have decreased resource sustainability) (Dumond 312). The disappearance of the Maya may be explained by a final depletion of resources to the support cities and a return to fully sustainable swidden agriculture. Raw population densities are not, however, the problem with swidden agriculture. In the Amazon, and many other rainforests, swidden harvesting may support up to one hundred and thirty people per square mile (Dumond 308). The structure of the swidden system makes it difficult to export the resources, discouraging the development of cities. When cities do arise they tend to encourage more traditional farming, which gives short-term gains in productivity but cannot sustain forest resources.

As native peoples grow in population and come under economic pressure from governments to support cities they must abandoned key aspects of swidden agriculture. Native Amazonians tend to practice the most pure and traditional forms of swidden agriculture, but other populations hybridize swidden with more western farming practices. The caboclos, or Brazilian peasantry, use methods similar to the natives but will also respond to market preferences and sacrifice some productivity for cash crops. The colonos, farmers that the Brazilian government moves to redistribute populations, are often unfamiliar with swidden practices and use more destructive processes that work in the temperate areas of Brazil (Dufour 658). Also, market demands encourage farmers to raise animals (Miller 162). Raising animals looses ninety percent of the productivity of a plot, because of all of the energy that the animals waste, causing the farmers to deplete the resources of the plot. The presence of greater population interacts synergistically with the negative consequences of market demands to support deforestation.

Recent developments, associated with political, economic and population pressures, cause swidden farmers to switch to slash-and-burn farming and deforestation. While slash-and-burn farming often does use different, and less diverse, plantings than swidden, the main difference is the fallow time. Even under sustainable systems, complete plot recovery can take up to one hundred years (Dufour 655). Native peoples determine fallow periods based on their need of land (Fox 524); as populations increase and need more resources, fallow periods decrease. When farmers abandon the swidden system entirely, in favor of slash-and-burn farming, they receive gains for a year or two in exchange for long-term fertility failure (Fox 251). To complicate the problem, when people receive more food they tend to reproduce more, increasing the future resource demand. Also, recovery time increases geometrically with forest disturbance – the more forest that people remove the lesser the strength of the remaining forest. The result is a positive feedback loop in which people demand more resources out of a weakening ecosystem, encouraging further desperation and deforestation.

The deforestation positive feedback loop has global consequences because of the importance of the rainforests for carbon sequestration. The Amazon rainforest stores massive amounts of carbon, held in the bodies of its trees and animals (Flannery 198). When farmers burn the forest it not only releases this stored carbon but also influences the rain cycle over the whole area. Changes in precipitation patterns detract from the ecosystem resilience, making it more susceptible to further deforestation (Flannery 197). Additionally, a release of carbon from burning contributes to global warming, which also changes precipitation patterns and make the remaining rainforest more vulnerable. When one combines the global warming and rain feedback positive loop with the anthropogenic positive feedback loop a synergistic interaction occurs that jeopardizes the existence of the rainforests and further feeds global warming.

Overpopulation causes the much of the pressure on farmers to shift from swidden agriculture to slash-and-burn farming for the purpose of supporting cities and market economies (Miller 162). An ideal solution, considering the ability of swiddens to support relatively high population densities, is for farmers to return to the swidden system (Fox 527). The ideal cannot be reached because returning to swidden agriculture does not address any of the issues that caused its demised. Unless Brazil can commit to removing market pressures from Amazonian populations, and these populations do not grow themselves, the cycle of deforestation must continue. Given the importance to the entire world of maintaining the rainforest to stem global warming, developed countries may want to offer such assistance. To stop deforestation, and hence to limit global warming, entire societies around the rainforest must be restructured to eliminate population and market pressures.

Literature Cited

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