Raised Field Farming versus Slash-and-Burn
Despite slash-and-burn’s risk of starting uncontrolled fires, depleting soil nutrients, and adding carbon emissions to the atmosphere, it is being championed by some as an effective method of forest clearance. Especially popular with some smallholders who cannot afford more expensive methods of land clearance, slash-and-burn involves felling trees and burning them when they dry out. It is declared illegal by many governments.
However a study featured in SciDev earlier this year claimed that slash-and-burn method furnish more beneficial growing conditions for new trees. Comparison of cleared areas using clear-felling, bulldozing, and slash-and-burn showed that slash-and-burn areas provided the best conditions for mahogany. In addition, other commercially valuable tree species thrived in the areas. Laura Snook, one of the authors of the study, says that the burning releases nutrients in (slashed-and-burned) trees and makes them available to new trees.
Another research study published in PNAS (Proceedings of the National Academy of Sciences) this April may challenge the earlier study’s conclusion that slash-and-burn is the best method for managing land in preparation for agriculture, particularly seasonally-flooded savannahs.
The latest study focuses on an ancient technique developed by farmers to manage their land without resorting to frequent burning. Raised-field farming was practiced by local farmers 800 years ago before Europeans settled inLatin America.
In raised-field farming, small-scale agricultural mounds were built to promote drainage and soil aeration, and to retain moisture. According to SciDev, this practice conserves soil nutrients and organic matter while preserving soil structure. Jose Iriarte, a researcher at the University of Exeter, UK, said that paleoecologists generalized that slash-and-burn was practiced in the past from observing modern indigenous farmers in savannah environments. But this was hardly the case, as the later study’s findings showed that very low frequencies of charcoal particles in the savannahs of French Guyana did not support the supposition of frequent use of slash-and-burn in the past. The full report can be seen at the PNAS’ site.
The study suggests that raised-field farming can be a more productive, more sustainable land use method for modern farmers minus the carbon emissions generated from slash-and-burn.
Snook says in an interview that policymakers may be unaware that fire is a natural phenomenon occurring in many forests and important in sustaining diversity.
A flaw in this analogy may be pointed out in that slash-and-burn occurs more frequently compared with natural forest fires, because it is driven by human intention rather than natural conditions.
Just as forest fires occur naturally (and so compared to slash-and-burn), it may also be pointed out that a form of raised-field method can also be observed in nature.
An unlikely relationship between termites, trees, and the seasonal floodplain of Okavango delta was featured in an earlier post. The Okavango Delta is a flat wetland visited by huge seasonal floods, bringing water and life to the Kalahari Desert. But, as the water from the Okavango River carries salt, it would poison the delta. The water is cleansed of the salt through the thousands of trees’ roots where salt deposits accumulate.
But the trees themselves would not grow and survive in the seasonally flooded delta were it not for the termites’ work. Termites need air vents to regulate the temperature in their tunnels, and they do this by building turret-like soil structures several feet high. The ‘raised’ mounds of soil enable trees to become established above floodwater-level and do their part in cleansing the water that floods the Okavango delta.
The trees thrive year after year, without the need for fires to ‘cleanse’ and replenish the nutrients of the area’s soil. In raised-field farming, studies also show that decomposed leaves, plant matter, etc. left by the seasonal floods on raised-field canals provided rich nutrients for growing plants and trees.
Slash-and-burn may be a good method as far as easy-and-cheap is concerned, but raised-field farming sounds a lot more ‘eco-friendly’ and ‘sustainable’.
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