They often act as intermediaries in the trade of goods such as polished stone axes, salt, and especially prestige items such as the plumes of the bird of paradise. See SS IV for detailed information on these groups. Originally covered in forests they are now densely occupied by man and heavily deforested. The Highlands are an area of high reliefs with deep valleys in between. Highland societies are engaged in intensive horticulture based on sweet potato and pig husbandry.
Population densities are high.
Though primarily cultivators engaged in swidden agriculture on grasslands, all Highland societies rely on the remaining forest environment , either higher up or on the edge of the mid-mountain plateaux. Highland peoples show great respect for the forest, even fear, and many beliefs are linked to it. The wild forest and mountains stand in opposition to the village and cultivated fields. Strong population pressure together with very high growth rates have lead to intensive deforestation, replacing primary forest by grasslands. This is precisely what drives people nowadays to exhaust the land, seek virgin lands on the fringes, and increasingly clear the surrounding mid-mountain forests for firewood and timber.