Slash-and-burn is one of the oldest agriculture types. These days, ill-effects of slash-and-burn agriculture attract more attention than its benefits. Here is some interesting information about the method, such as its origins, meaning, benefits, major drawbacks, along with steps involved and where it is practiced.
Did You Know?
The burning of forests for slash-and-burn agriculture in the Amazon basin is visible from outer space.
Shifting agriculture is a type of farming in which a part of a forest is cleared to obtain land for growing crops. The crops thrive only on the inherent fertility of the soil itself; no external fertilizers are added. After successive cycles of crops deplete the amount of nutrients found in the soil, production gradually becomes inadequate.
Also, all this while, weeds constantly compete with the crops. Once the harvest decreases to an unacceptable limit, or if weeds completely take over the field, it is then abandoned so that natural vegetation can reclaim the land. Cultivation is then carried out on another part of land, after clearing it of all vegetation. This process continues.
It’s obvious that such kind of agriculture comes with its share of drawbacks. While damage to the forest and its inhabitants is the direct result, shifting agriculture is also criticized for draining the fertility of soil, and being unsustainable.
This is especially true in the present situation, where every patch of forest is vital for purifying the air of its noxious pollutants, and for sheltering the planet’s dwindling wildlife. Of all the types of shifting agriculture, slash-and-burn is the most widespread and infamous.
Slash-and-burn Method Meaning
Slash-and-burn agriculture, also called swidden or Jhum agriculture, is the temporary cultivation of a part of land which has been cleared of its natural forest cover by starting a fire. The ownership of the land belongs to the family which clears and cultivates the land, until loss of soil fertility prompts them to abandon it and move to another site.
Years later, when growth of natural vegetation makes the site fertile again, it can be reclaimed and cleared by another family for cultivation. Most slash-and-burn agriculture is carried out in tropical forests and grasslands.
Slash-and-burn agriculture is estimated to be carried out by about 200 to 500 million people around the globe, about 7% of the current human population. Although it was earlier carried out in temperate regions, it is more common in the tropics now, with almost half the land in the tropical regions currently being under this form of cultivation.
It is carried out in parts of Central Africa, northern regions of South America, and parts of Southeast Asia. The origins of slash-and-burn agriculture can be traced back to 12,000 years ago, in the Neolithic Age, which saw great advances in agricultural implements.
This was the main reason why man could shift from his hunter-gatherer lifestyle to a stable agricultural one, leading to a spurt in the human population.
Steps in Slash-and-burn Method
► Using simple implements like axes, the trees in a particular region are slashed, i.e., cut, and allowed to lie where they are. Species which provide timber, fodder for cattle, and food for man, may be spared.
Burning of Forest
► The cut trees and plants are allowed to lie in the field till the next dry season so that they can dry out. Just before the onset of the rains, the biomass, i.e., the plant and tree matter, is set on fire. The ash produced will make the soil fertile for cultivation.
► In the regions that receive a lot of rain, which makes drying of the biomass difficult, it is allowed to decompose in the moist conditions, rather than burning it. This releases nutrients from the biomass into the soil, just like burning.
Clearing is Formed
► With the arrival of the rains, crops are sown in the ash-covered field. From then on till the harvest season, farmers are preoccupied with removing weeds which may compete with the crop. Chopped vegetation from other regions may be spread over the field as mulch.
Clearing is Cultivated
► The field is cultivated in multiple cycles, until the soil loses its fertility due to successive cultivation. Then the site is abandoned for a few years to allow the natural vegetation to take over and replenish the soil fertility.
► Farmer move on to clear another forested patch by slash-and-burn, till the earlier field regains its fertility, at which point, it is deforested and cultivated again.
► It is the easiest way to clear a tract of land for cultivation. If one hectare of tropical forest is cleared, it will produce around 500 tons of biomass, which would take at least 3 years to decompose and free the land for plantation. Slash-and-burn makes this process much quicker, economical, and requires less labor.
► This method is sustainable in less populated areas, or where a large forest is available. This has traditionally been the case, and low populations allow a cultivated field to be left fallow for at least 15-20 years, which is enough to restore its fertility.
► This has been type of agroforestry, where crops were grown surrounded by trees. This caused disruption to ecosystem, but resembles natural disturbances experienced by forests. Modern agriculture follows monocropping system, where one type of crop is cultivated. All trees in a patch of land have to be felled for movement of modern agricultural equipment.
► Burning a patch of forest kills and drives away pests that would have attacked crops. Besides, it allows any parasites or predators of these pests to enter the crop from surrounding forests to control their infestation.
► The fires can help local tribes in capturing game animals from the forest for their food requirements.
►This form of agriculture, while allowing a hand-to-mouth existence for farmers, keeps them in poverty. This is due to decreasing harvest as soil fertility diminishes. Also since the field is to be abandoned after few years, farmers have to move far, and they cannot guard cash crops from robbers at night. They have to take long daily walks.
► As the returns diminish, people may be forced to seek alternative sources of income, or try their luck in cities, where they may have to endure life in the slums.
► Despite the weeding operations carried out by farmers, in most cases, weeds successfully grow on the field. The labor required to remove all weeds from an infested crop is usually lesser than that of clearing another patch of forest, so farmers may be prompted to slash and burn other regions too.
► This system requires 15 – 30 hectares of land to be cultivated, just to feed a single person, due to diminishing harvest and long fallow periods.
► Slash-and-burn is not suited to modern situations, which involve large populations living around shrinking forests. In such cases, the period when the land is left fallow, so that natural vegetation can reestablish itself, may be 3 – 5 years as compared to the recommended 15 – 20 years. This does not allow nutrients to return to the soil properly.
On the Environment
► Several rare species of plants and animals are threatened by the burning of forests. Besides, the maximum variety of flora and fauna is found in tropical forests, many of which are endangered.
► The fires can rage on for days, or weeks, until the biomass is completely burned off. This releases large amounts of gases like carbon monoxide and dioxide, sulfur dioxide, and nitrous oxide, which contribute to global warming and climate change. It is thought that slash-and-burn causes twice as much air pollution as that caused by annual air travel.
► The soil in tropical forests is naturally infertile, as the moist conditions cause microbes to degrade all the beneficial organic matter found in the soil. But forest trees are well-adapted to such conditions, and they absorb nutrition from the soil, and concentrate it in their tissues.
Thus, most of the nutrients in tropical forests are found in the trees, rather than the soil. While the ash formed on burning returns most of these nutrients to the soil, it is quickly depleted in just 3 to 4 crop cycles, after which the land has to be abandoned.
► If slash-and-burn is used in an unsustainable manner, it may take more time than fallow period for the land to regain lost fertility.
► It can cause accidental forest fires in other parts of the forest. Each year, Amazon rainforest experiences 2,000 to 3,000 accidental fires. Once, a 250 × 370 mile-area of forest was completely devastated by such a fire.
► Clearing forest vegetation contributes to soil erosion, by helping wind and flowing water carry away soil, which would have otherwise been tightly held by tree roots. Besides reducing soil fertility, this increases the occurrence of landslides and floods.
► The soil carried away by wind and water enters water bodies and forms sediment. This reduces the sunlight entering the water, which causes the death of corals in oceans. Since corals shelter a large number of fish, fishermen catch will be reduced, increasing poverty in the region.
Due to the ill-effects of slash-and-burn, efforts are being made to promote alternative systems of agriculture. This includes alley cropping, in which crops are grown in between rows of natural forest trees, and crop rotation, in which two crops are grown successively. The second crop returns those nutrients to the soil, which the first has removed.