Print PageIntensive agriculture on Rapa Nui supported a population with sufficient surplus labor to create and transport the massive statues for which the island is famous. However, comparisons with pre-contact agricultural systems in Hawaii – and the soils that supported them – suggest that most Rapa Nui soils are marginal in fertility compared to those on which intensive rain-fed systems were developed and sustained in Hawaii. We evaluated soil nutrient availability and Nb-based geochemical indices of weathering intensity within and surrounding several rock gardens across Rapa Nui, and analyzed fine-scale variation in soils in the Anamarama region. Rock gardens there surround outcrops of basaltic rock; both natural and cultural processes have removed rocks from the outcrops and scattered them on the surface nearby.
Results/Conclusions
Soils on the steep sides of the outcrop were little-weathered and low in resin-available P (~ 20 ppm); those on gentle slopes with surface rock cover were moderately weathered and high in resin P (100 – 120 ppm), and those between outcrops were highly weathered and intermediate in resin P (40-60 ppm). We conclude that Rapa Nui cultivators intensified agriculture on the gradual slopes where erosion and deposition had created a fringe of higher soil fertility – and that their activities may have improved soil fertility in these “sweet spots”. In contrast, Hawaiian cultivators intensified agriculture in landscape-level biogeochemical sweet spots tens of square kilometers in size.
