Shifting cultivation
In this type of farming, a patch of forest land is cleared by a combination of felling (chopping down) and burning, and crops are grown. After 2–3 years the fertility of the soil begins to decline, the land is abandoned and the farmer moves to clear a fresh piece of land elsewhere in the forest as the process continues. While the land is left fallow the forest regrows in the cleared area and soil fertility and biomass is restored. After a decade or more, the farmer may return to the first piece of land. This form of agriculture is sustainable at low population densities, but higher population loads require more frequent clearing which prevents soil fertility from recovering, opens up more of the forest canopy, and encourages scrub at the expense of large trees, eventually resulting in deforestation and soil erosion. Shifting cultivation is called "dredd" in India, "ladang" in Indonesia, "milpa" in Central America and Mexico and "jhumming" in North East India.