Slash-and-burn agriculture, sometimes known as swiddening or shifting cultivation, involves felling trees and vegetation on a plot of land, leaving them to dry, and then setting fire to them. Crops planted on the plot benefit from the nutrients provided by the ash. A diversity of crops tend to be planted and intermingled with each other. Depending on the fertility of the soil, once cleared, a plot is used for a further 2 to 5 years before being left to fallow. The reasons for abandoning plots vary. It may reflect decreased soil fertility, excessive weeding effort, or combinations of both.
Slash-and-burn agriculture has been widely practiced in human history. It is still extensively used in tropical forests, where some 250 to 500 million people are thought to practice it. Slash-and-burn agriculture can also be viewed as an extensive early stage in the evolution of agricultural practice to more intensive measures. Depending on the fallowing time, it will require 10 to 30 hectares per person. The fallowing period will decline with the increasing population density, with attendant consequences for soil fertility and agricultural practice. But where slash-and-burn agriculture is not practiced just for subsistence, but is one of several pursuits within more diverse livelihoods, it will be less directly dependent on population density.
Slash-and-burn agriculture has its advocates. It minimizes human effort, while maximizing the input of energy from burnt vegetation. It can leave larger trees protecting the soil from vigorous rains. The timing of the burns, the temperature of the flames, and planting the right mix and rotation of crops can take considerable skill.
But slash-and-burn agriculture has rarely been popular in development or conservation circles. It was castigated in the early years of agricultural development for being wasteful and inefficient or lazy. This overlooked both its productivity, per person, and the ecology of intercropping. It is currently widely criticized for its impact on biodiversity conservation where habitat conversion is assumed to be driven by increasing populations and intensity of use. The threats are real, but these criticisms can exaggerate the blame due to small holders, when more profound forces drive their action. They also privilege the role of population growth, when other forces are more significant. Finally, they can overplay the detrimental consequences of anthropogenic disturbance, without acknowledging that disturbance can foster biodiversity at some scales.
References:
- Lambin, E. F., Turner, B. L., Geist, H. J., Agbola S. B., Angelsen, A., Bruce, J. W., et al. (2001). The causes of land-use and land-cover change: Moving beyond the myths. Global Environmental Change, 11, 261-269.
- Moore, H., & Vaughn, M. (1994). Cutting down trees. Gender, nutrition, and agricultural change in the northern province of Zambia, 1890-1990. London: James Currey.
- Sponsel, L. E. (1995). Indigenous peoples and the future of Amazonia: An ecological anthropology of an endangered world. Tuscon: University of Arizona Press.
