1. Slash-and-burn agriculture has been practiced for millennia in tropical count
ID: 29593 • Letter: 1
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1. Slash-and-burn agriculture has been practiced for millennia in tropical countries throughout the world. In this form of agriculture, some timber may be harvested from tropical forests prior to their conversion to agricultural use, but most of the aboveground biomass is cut and burned on site. Agricultural crops are planted immediately following burning. Recently, there has been increased pressure to harvest all timber (for transport off site) from tropical forests prior to their conversion to agriculture. What are the implications of such complete harvest for the success of subsequent agricultural activities on oligotrophic soils in the tropics?Explanation / Answer
Although a solution for overpopulated tropical countries where subsistence agriculture may be the traditional method of sustaining many families, the consequences of slash-and-burn techniques for ecosystems are almost always destructive.[citation needed] This happens particularly as population densities increase, and as a result farming becomes more intensively practiced. This is because as demand for more land increases, the fallow period by necessity declines. The principal vulnerability is the nutrient-poor soil, pervasive in most tropical forests. When biomass is extracted even for one harvest of wood or charcoal, the residual soil value is heavily diminished for further growth of any type of vegetation. Sometimes there are several cycles of slash-and-burn within a few years time span; for example in eastern Madagascar the following scenario occurs commonly. The first wave might be cutting of all trees for wood use. A few years later, saplings are harvested to make charcoal, and within the next year the plot is burned to create a quick flush of nutrients for grass to feed the family zebu cattle. If adjacent plots are treated in a similar fashion, large-scale erosion will usually ensue, since there are no roots or temporary water storage in nearby canopies to arrest the surface runoff. Thus, any small remaining amounts of nutrients are washed away. The area is an example of desertification, and no further growth of any type may arise for generations. The ecological ramifications of the above scenario are further magnified, because tropical forests are habitats for extremely biologically diverse ecosystems, typically containing large numbers of endemic and endangered species. Therefore, the role of slash-and-burn is significant in the current Holocene extinction. Slash-and-char is an alternative that alleviates some of the negative ecological implications of traditional slash-and-burn techniques.
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