The most significant difference between the two is that slash-and-burn is associated with raising field crops, while nomadism usually involves herding livestock.
Farmers have practiced slash-and-burn agriculture, which is also referred to as shifting cultivation or swidden agriculture, in almost every region of the world where farming is possible.
Although at the end of the twentieth century slash-and-burn agriculture was most commonly found in tropical areas such as the Amazon River basin in South America, swidden agriculture once dominated agriculture in more temperate regions, such as northern Europe. Swidden agriculture was, in fact, common in Finland and northern Russia well into the early decades of the twentieth century.
Slash-and-burn acquired its name from the practice of farmers who cleared land for planting crops by cutting down the trees or brush on the land and then burning the fallen timber on the site. The farmers literally slash and burn.
The ashes of the burnt wood add minerals to the soil, which temporarily improves its fertility.Crops the first year following clearing and burning are generally the best crops the site will provide. Each year after that, the yield diminishes slightly as the fertility of the soil is depleted.
Farmers who practice slash-and-burn do not attempt to improve fertility by adding fertilizers such as animal manure to the soil. They instead rely on the soil to replenish it-self over time.
When the yield from one site drops below acceptable levels, farmers then clear another piece of land, burn the brush and other vegetation, and cultivate that site while leaving their previous field to lie fallow and its natural vegetation to return.
This cycle will be repeated over and over, with some sites being allowed to lie fallow indefinitely, while others may be revisited and farmed again in five, ten, or twenty years.
Farmers who practice slash-and-burn do not always move their dwelling places as they cultivate different fields. In some geographic regions, farmers live in a central village and farm cooperatively, with fields being alternately allowed to remain fallow and farmed, making a gradual circuit around the central village.
In other cases, the village itself may move as new fields are cultivated. Anthropologists studying indigenous peoples in Amazonia, for example, discovered that village garden sites were on a hundred-year cycle. Villagers farmed cooperatively to clear a garden site. That garden would be used for about five years; then a new site was cleared.
When the fields in use became an inconvenient distance from the village—about once every twenty years—the entire village would move to be closer to the new fields. Over a period of approximately one hundred years, a village would make a circle through the forest, eventually ending up close to where it had been located long before any of the present villagers had been born.
In more temperate climates, farmers often owned and lived on the land on which they practiced swidden agriculture. Farmers in Finland, for example, would clear a portion of their land, burn the covering vegetation, grow grains for several years, and then allow that land to remain fallow for five to twenty years.
Although slash-and-burn is frequently denounced as a cause of environmental degradation in tropical areas, the problemwith it is not the practice itself but the length of the cycle.
If the cycle of shifting cultivation is long enough, forests will grow back, the soil will regain its fertility, and minimal adverse effects will occur. In some regions, a piece of land may require as little as five years to regain its maximum fertility; in others, it may take one hundred years.
Problems arise when growing populations put pressure on traditional farmers to return to fallow land too soon. Crops are smaller than needed, leading to a vicious cycle in which the next strip of land is also farmed too soon, and each site yields less and less. As a result,more and more land must be cleared.
Nomadic peoples have no permanent homes. They earn their living by raising herd animals, such as sheep, horses, or other cattle, and they spend their lives following their herds from pasture to pasture with the seasons, going wherever there is sufficient food for their animals.
Most nomadic animals tend to be hardy breeds of goats, sheep, or cattle that can withstand hardship and live on marginal lands. Traditional nomads rely on natural pasturage to support their herds and grow no grains or hay for themselves. If a drought occurs or a traditional pasturing site is unavailable, they can lose most of their herds to starvation.
In many nomadic societies, the herd animal is almost the entire basis for sustaining the people. The animals are slaughtered for food, clothing is woven from the fibers of their hair, and cheese and yogurt may be made from milk.
The animals may also be used for sustenance without being slaughtered. Nomads in Mongolia, for example, occasionally drink horses’ blood, removing only a cup or two at a time from the animal.
In mountainous regions, nomads often spend the summers high up on mountain meadows, returning to lower altitudes in the autumn when snow begins to fall. In desert regions, they move from oasis to oasis, going to the places where sufficient natural water exists to allow brush and grass to grow, allowing their animals to graze for a few days, weeks, or months, then moving on.
In some cases, the pressure to move on comes not from the depletion of food for the animals but from the depletion of a water source, such as a spring or well. At many desert oases, a natural water seep or spring provides only enough water to support a nomadic group for a few days at a time.
In addition to true nomads—people who never live in one place permanently—a number of cultures have practiced seminomadic farming: The temperate months of the year, spring through fall, are spent following the herds on a long loop, sometimes hundreds of miles long, through traditional grazing areas, then the winter is spent in a permanent village.
Nomadism has been practiced for millennia, but there is strong pressure from several sources to eliminate it. Pressures generated by industrialized society are increasingly threatening the traditional cultures of nomadic societies, such as the Bedouin of the Arabian Peninsula. Traditional grazing areas are being fenced off or developed for other purposes.
Environmentalists are also concerned about the ecological damage caused by nomadism. Nomads generally measure their wealth by the number of animals they own and will try to develop their herds to as large a size as possible, well beyond the numbers required for simple sustainability. The herd animals eat increasingly large amounts of vegetation, which then has no opportunity to regenerate. Desertification may occur as a result.
Nomadism based on herding goats and sheep, for example, has been blamed for the expansion of the Sahara Desert in Africa. For this reason, many environmental policy makers have been attempting to persuade nomads to give up their traditional life-style and become sedentary farmers.