The distribution of rock gardens on Rapa Nui (Easter Island) as determined from satellite imagery

Abstract

Rock gardens were the primary agricultural resource on Rapa Nui. These extensive features were constructed in a range of environmental and climatic zones. They provided agronomic advantages of enhanced wind protection and water permeability, reduced evapotranspiration and soil erosion, and possibly soil nutrient enhancement. Early European descriptions of Rapa Nui suggest ca. 10% of the island was covered by gardens, yet due to the lack of spatially extensive fine-grained data archaeologists have until recently not been able to document the distribution of these gardens. The analysis of highresolution WorldView 2 satellite data provides an accurate estimate of the total area of the island covered by rock gardens. A series of supervised classification techniques and filtering algorithms identifies several categories of rock gardens. The classifications were assessed with data from GPS-based surveys, and it was found that between 2.5 and 12.7% of the island's surface was covered with agricultural rock gardens. The gardens were located below an elevational threshold, indicating specific zones of agricultural productivity throughout the island. © 2012 Elsevier Ltd.