Deforestation rates in Papua New Guinea: How much does subsistence agriculture contribute?

Background/Question/Methods

Deforestation rates in Papua New Guinea (PNG) are more rapid than the Brazilian Amazon. While many factors have been linked to deforestation and land degradation in PNG, the relationship between agricultural practices and deforestation have not been fully examined. The effects of agricultural expansion has been overestimated in some areas due to the negative perception of swidden agriculture (slash-and-burn) and difficulties in discerning agricultural land from logged areas. The population of PNG has doubled over the past twenty years, and this research examines how swidden agricultural strategies (expansion, intensification, crop selection, etc.) contribute to forest and land cover changes. To assess agricultural strategy changes, in-depth interviews were conducted in a coastal village and responses were compared to satellite imagery of the agricultural areas. Satellite imagery using tasseled cap methods provided a platform to quantify land cover changes over time and these changes were then related to livelihood decisions. A seasonal perspective was also addressed using satellite images to help clarify differences among natural vegetation and cultivated plots. This novel combination of methodologies comprehensively explains the drivers behind forest and land cover changes, allowing for a more accurate assessment of deforestation rates associated with agricultural practices. 

Results/Conclusions

Temporal analysis of the satellite imagery revealed that cultivated area in PNG has increased by 9% between 1992 and 2010 despite an estimated population growth of 190% over this period. Interviews supported these observations and the strategies described were those of intensification and primarily included 1) shortened fallow periods, 2) an increased number of crops planted per area and year, and 3) changes in cultivars planted and new crop introductions.  Intensified agriculture has had adverse effects on crop yields such as decreases in soil fertility and increases in pest problems, thus furthering the need for additional strategies to increase yields. Although soil quality and fertility cannot be directly studied using satellite images, the percentage of crop cover verses soil brightness was assessed. Overall, the amount of solar radiation reflecting from the soil (soil brightness) has decreased by 30%, suggesting that crop coverage and density has increased.  This was also supported by an observed increase in vegetation cover in the agricultural areas. These results suggest that subsistence agriculture has influenced land cover changes, but has not been a major contributor to deforestation rates in this region of PNG.