The ecology of Huli subsistence agriculture

A detailed study of the ecology of subsistence agriculture in the Tari Basin was conducted to investigate the stability of intensive agroecosystems in the highlands of Papua New Guinea. The highly intensive agricultural systems that have evolved in the wetland environments in the lowest parts of the basin were found to be extremely stable and capable of further intensification. Both soil fertility and sweet potato yields showed no signs of degradation even though some areas had been under continuous cultivation for hundreds of years. In the dryland environments with volcanic ash soils there was evidence of ecological instability in the form of declining soil fertility and sweet potato yields over time and the progressive replacement of forest vegetation with grasslands having a much lower biomass and nutrient content. Higher altitude dryland environments were the most susceptible to degradation due to lower fertility soils, higher rainfall and higher rates of soil loss by erosion. The Huli people have responded to these differences in ecological stability by concentrating their agricultural activities increasingly on to the more fertile wetland areas. Much of this movement into the lower parts of the basin is thought to have occurred in the period since European contact, over the last 50 years. These findings have implications for much of the Papua New Guinea highlands where volcanic ash soils occur. Although these soils are highly suitable for growing sweet potato and have been able to support large rural populations with their pigs, they are unable to remain productive under continuous cultivation even though the cropping practices of most highland groups are well adjusted to conserving soil fertility and maximizing crop yields. The chemical fertility of volcanic ash soils is being progressively depleted and much greater efforts are needed to promote the restoration of soil fertility during the fallow period. Much greater emphasis is needed on improving fallow practices such as the promotion of woody regrowth and forest regeneration and the growing of leguminous cover crops to protect soils against erosion and to provide a large volume of nutrient-rich plant material suitable for composting.