Slash and burn agriculture is a traditional method of land clearing, also known as shifting cultivation or swidden agriculture. It involves cutting down existing vegetation and burning it to prepare land for temporary crop cultivation.
Defining Slash and Burn
Slash and burn agriculture is a cultivation method where forests are cleared by cutting and burning plants to create arable land. It represents a form of shifting cultivation, where a plot is farmed for a short period before being left to regenerate naturally. The process involves “slashing” or cutting down vegetation, which is then burned to form a field called a “swidden.” This ancient practice dates back at least 7,000 to 12,000 years, coinciding with the Neolithic Revolution. Today, an estimated 200 to 500 million people globally, about 7% of the world’s population, still employ this method.
The Practice in Detail
The process begins with selecting a plot, typically in a forested or overgrown area. Farmers cut down trees and other woody plants, exposing the land to sunlight. The cut vegetation, or “slash,” is then left to dry, usually timed before the rainy season for an effective burn.
Following the drying period, the biomass is intentionally set on fire. This burning clears remaining vegetation and releases nutrients from the ash into the soil. Crops like maize, cassava, or rice are then planted directly into the nutrient-enriched ash.
This cultivation period generally lasts one to five years, until the soil’s fertility begins to decline. Once productivity decreases, the plot is abandoned and enters a “fallow” period. This allows natural vegetation to regrow and the soil to recover its fertility, which can take 5 to over 20 years.
Reasons for its Use
Communities in tropical regions adopt slash and burn agriculture for several practical reasons. The method provides a quick and efficient way to clear dense vegetation, making land suitable for cultivation. A primary advantage is the immediate addition of nutrients to the soil. The ash from burned vegetation acts as a temporary fertilizer, supplying elements like potassium, phosphorus, calcium, magnesium, and other micronutrients.
The burning process also offers a temporary solution for pest and weed control, eliminating unwanted plant species and reducing pest populations. This agricultural technique requires minimal financial investment, relying on simple hand tools like machetes and axes. This makes it accessible to subsistence farmers with limited resources. The method is also well-suited for tropical environments, where soils are often poor in nutrients and heavy rainfall can quickly leach them away.
Consequences for Ecosystems and Communities
Despite its perceived benefits, slash and burn agriculture carries broader consequences for ecosystems and human communities. It contributes to tropical deforestation and the resulting loss of diverse plant and animal habitats. When land is repeatedly cleared, it leads to habitat fragmentation and a reduction in biodiversity. The practice also causes soil degradation over time.
While the initial burn enriches the soil, repeated cycles and insufficient fallow periods deplete fertility. This leaves the soil vulnerable to erosion, especially on sloped terrains, as heavy rains can easily wash away topsoil without protective tree roots. The burning of biomass releases smoke, contributing to regional air pollution. This also results in greenhouse gas emissions, including carbon dioxide, methane, and nitrous oxide, which contribute to global warming.
For instance, burning just one hectare of dense forest can release between 70 to 300 Mg of carbon into the atmosphere. Socially, the increased scale of this practice can lead to the displacement of indigenous communities and conflicts over land resources. While historically sustainable in areas with low population density, accelerated rates due to growing populations render the method unsustainable in many modern contexts.