"Most secondary forests in the mountainous parts of mainland Southeast Asia owe their origin to swidden farming. Secondary forests are defined here as ?forests regenerating largely through natural processes after significant human disturbance of the original forest vegetation at a single point in time or over an extended period, and displaying a major difference in forest structure and/or canopy species composition with respect to nearby primary forests on similar sites” (Chokkalingam et al. 2000). Swidden farming, practised by minority groups referred to as hill tribes or hill people, was the dominant form of land use in mainland Southeast Asia until the 1960s. This is still the case in most of this region except maybe in northern Thailand. Occupants of the lowlands only recently began to encroach into the highlands to practice supplementary swidden cultivation, using short cultivation and fallow periods that result in a severely degraded version of secondary growth dominated by thorny species. Swidden farming as practised by upland minorities is of two types. Rotational swidden farming applies short cultivation and long fallow periods, during which swidden fallow secondary forests establish rapidly over the course of several successional stages. Swidden fallow secondary forests are defined here as ?forests regenerating largely through natural processes in woody fallows of swidden agriculture for the purposes of restoring the land for cultivation again” (Chokkalingam et al. 2000). Pioneer swidden farming has longer cultivation periods and an irregular fallow length, which is dominated by weeds and grasses for a long time before secondary forests regenerate. In some regions, these two types of swidden farming can be correlated to specific ethnic groups and altitudinal zones. Rotational swiddening is mainly practised at intermediate elevations between 600 and 1000 m by ethnic groups that are long-time residents in comparison to more recent immigrants, who practise pioneer swiddening at altitudes above 1000 m..."