Soils, agriculture, and land use in island socio-ecosystems: Three case studies from Southeastern Polynesia

The availability of nutrient-rich soils capable of supporting intensive cultivation was a key factor in the relative vulnerability and resilience of traditional Polynesian societies, whose economies were based on agricultural production. We tested the hypothesis that geological age was a key controlling factor in determining the nutrient status of island soils, extensively sampling soils on two islands and a small archipelago in southeastern Polynesia: Mo'orea (1.5-1.72 Ma), Maupiti (3.9-4.5 Ma), and the Gambier Islands (5.6-6.3 Ma). Rather than supporting a hypothesis of island age primarily determining soil fertility, our results indicate that topographic relief, the presence of active slope processes such as landslides and mass wasting, and rainfall are more important controlling factors. Rejuvenation of soil nutrients due to mass wasting, in particular, appears to be the most important factor contributing to soil fertility. Our field surveys also provide archaeological evidence showing that precontact Polynesians were finely attuned to local soil properties, targeting high soil fertility areas for agriculture and reserving lower fertility areas for other land use practices.