Slash-and-burn

The slash and burn is a common technique for thousands of years, to clear primary or secondary forest areas mostly on the preparation of agricultural production with the use of fire.

Distinction between

Slash and burn is often used in the context of the so-called subsistence farming, which is used solely or predominantly of production for their own consumption, but not for the marketing of products. Another area of ​​application is, for example, the system of grazing areas, which are mostly used extensively due to lack of resistance under low stocking rates.

While in the past often abandoned in the context of shifting cultivation areas after the exhaustion of the available nutrient reserves in the system entirely in favor of new, untouched primary forest areas, it is now against the background of legally binding regulated ownership usually not readily possible. Other areas of slash and burn are eg infrastructure measures such as the exposure routes for road construction or removal of vegetation under power lines today.

Settlement history in Europe

Slash and burn can be, in connection with girdling, suspect as early as the Neolithic. At various stages of land reclamation in Europe Brandrodung was common. Dated to the Middle Ages can be about toponyms on brant, Brende or senge (s), sing (s) sang. In the 15th century, however, slash and burn is already criminalized, and the incipient Little Ice Age prohibits useless destruction of firewood. In wooded Scandinavia the method was practiced until the 19th century by the Forest Finns called.

Modern situation and problems in the tropics

The successful introduction of cash crops for marketing of various agricultural products requires controlled ownership structures, better training of small farmers, access to finance and related markets. Often, in the absence of other effective tools swidden is sometimes still used in equatorial regions such as northern Brazil or the Indonesian part of Borneo Kalimantan mentioned. Slash and burn is, for example, in the north Brazilian state of Pará operated by small farmers on 25 acre parcels that were inhabited since the mid-19th century; ownership were guaranteed by the state in the early 20th century.

Method

A foreseen for agricultural production area is often manually cleared at the beginning of the dry season, for example, with machetes, which can cost at 40 tonnes of dry matter per hectare to about 80 hours of work. If perennial plants such as Maracujá or pepper are grown, is to remove the above-ground vegetation to grub up the roots added. The logging debris is left lying for several weeks to dry and eventually infected. Quite often this is get the fire out of control and devastate whole regions: In the spring of 1998, an area the size of Belgium was in the northern Brazilian state of Roraima prey to the flames. In Southeast Asia, it comes in the months of May to October often lead to health problems through clouds of smoke arising in the context of Indonesian slash and burn. The governments of Malaysia and Singapore publish hourly readings of air pollution on the internet. In June 2013, the measured values ​​reached in both countries due to more than 130 fires in Indonesia for the first time the " dangerous". Previously, the high-water mark was in 1997 in the " very unhealthy ". Through the air pollution outside political tensions over Indonesia develop in the countries concerned. Even animals are threatened by the fires. In the tropical rain forest, however, there is little risk that there will be larger forest fires as a whole, there is a very humid climate and rivers everywhere would the fire blocking the way.

Demographic factor

Slash and burn was under the precondition sparse population until the 19th and beginning of the 20th century a perfectly sustainable technology, as after land clearing and cultivation cycle was followed by a sufficiently long fallow period of about 15 years. This gave the secondary forest, known in Brazil Capoeira ( as the eponymous martial art Capoeira ), opportunity for adequate regeneration, because nutrients such as nitrogen, but also mineral nutrients such as potassium or magnesium replenished over time, including through atmospheric deposition again and have been established in the vegetation. With massive population growth since the 19th century, the floors were, however, often exhausted by too fast production cycles, as the fallow period has been reduced to less than 5 years.

Effect on the nutrient cycle

Basic problem of slash and burn is the distribution of nutrients in tropical ecosystems. In the soils of temperate European latitudes about 80 % of the nutrients in the soil and only 20% in the vegetation are stored. In the equatorial red laterite soils, this ratio is reversed: you are exposed for tens of thousands of years of heavy physical and chemical erosion by sunlight and very high rainfall. In consequence, a " short-circuited " nutrient cycle has developed through decomposition of biomass released nutrients are very quickly absorbed by other plants, so they do not wash out over the floor. The soils of the temperate latitudes, however, were, for example, layered new from the last ice age and enriched with nutrient- rich sediments such as loess; Moreover, local soils relatively low rainfall and thus reduced leaching are exposed.

Slash and burn mobilizes stored in the biomass nutrient capital and makes it available in agricultural production. The fire is not only the carbon previously bound -free and thus contributes to the greenhouse effect. It evaporate during firing, according to studies also up over 90 % of the nitrogen contained in the biomass and to over 40% of mineral nutrients such as potassium or magnesium. The remaining ash is used as fertilizer for the production of eg maize or cassava. For small farmers, this ash - fertilization usually the only affordable Input out to promote their production. The use of fertilizer or own machine comes for it usually out of the question, however, there is sometimes a rental system for machines.

Critical is the slash and burn through the depletion of depleted soils and the subsequent exodus of small farmers to new, unused space. Thus, the pressure grows on previously untouched forest areas, fulfill the ecologically important functions, for example, to safeguard biodiversity because forests provide most terrestrial species habitat, but also as a carbon sink for determining the greenhouse gas carbon dioxide are used. Where the forest has to give way to the pastures of large landowners, the floor is wounded by cattle kick and exposed severe erosion, so that a return of the forest may be impossible. In contrast, the traditional slash and burn taught at barely damage to forests, the regular fire even reduced the risk of forest fires in affected areas. Only the massive and extensive use of slash and burn without subsequent adequate fallow, as for the recovery of pastures, causing permanent damage to the natural environment.

Alternative methods

Due to social conditions, the fire clearance can not be adjusted or forbidden readily, without depriving millions of people of their livelihood. It is therefore of finding opportunities to optimize the slash and burn system in a socially acceptable through improved productivity and sustainability, approaches are:

• Improve soil substrate eg with charcoal to better bind nutrients.
• Enrichment of the regrowing secondary vegetation of fast-growing tree species that reach a high biomass volume in a short time, and legumes, the nitrogen from the air bind and accumulate on the surface.
• Replace the firing by mulching, that is, machine grinding the biomass and leaving on the surface so that the released in the course of rotting nutrients remain on the surface. A Gehölzmähhäcksler developed for this purpose, the Institute of Agricultural Engineering at the University of Göttingen.
• In the cultivation of the forest floor is not destroyed. On the upper floor are large trees, such as coconuts or Brazil nuts, used. In the lower floor, the farmers harvest bananas, citrus fruits, papayas or mangoes. On the ground grows vegetables and soil cassava and yams.