Nevertheless, important intervillage ties do exist. Marriage often takes place between individuals from different villages, and persons residing in separate villages often come together on ceremonial occasions. Members of culturally and linguistically related villages collectively constitute a tribe, a sociocultural unit that may contain tens of thousands or even hundreds of thousands of persons.
Most simple horticulturalists in recent times have lived in heavily forested environments and practice a form of cultivation known as slash-and-burn (also known as shifting cultivation). This cultivation technique involves cutting down a section of forest growth and then setting fire to the accumulated debris. The remaining ashes serve as a fertilizer, and usually no other fertilizer is added. The crops are then planted in these cleared plots (usually no more than an acre in size) with the aid of a digging stick, a long pole with a sharpened and fire-hardened end. A given plot may be devoted to a single crop, but a more common practice is to plant several minor crops along with one main staple (Sahlins, 1968). The task of clearing and preparing the plots generally falls to the men, while that of planting and harvesting is most often carried out by women.
Since wood ashes generally serve as the only fertilizer, slash-and-burn cultivation is associated with short-term soil fertility. Freshly produced ashes are washed away by rain after a year or two, and for this reason a plot of land can only be cultivated for that length of time. It must then be allowed to remain fallow long enough for the forest to regenerate so that new ashes can be produced. The fallow period ordinarily lasts approximately 20 to 30 years. When the forest growth has returned, the process of cutting, burning, and cultivating can begin again.