In his book "Collapse", Jared Diamond highlights the spectacular and mysterious collapse of civilisation on Easter Island. Diamond outlines a number of factors leading to success or failure of civilisations. We have identified that one of these factors - fragile soils - allows us to hypothesise that Easter Islanders would have overshot the carrying capacity of their landscape, reaching maximum population as soil nutrient depletion caused declining crop yields. We propose isotope, biomarker and DNA approaches to reconstruct the biogeochemistry of collapse and thereby test whether the timing of nutrient depletion can answer the question: "Why did they cut down the last tree?"
Within dormant volcanic craters where settlement occurred, we will obtain carefully located cores to precisely resolve the timing of changes in plant, animal and human populations, as well as soil fertility. We will examine plant microfossils (e.g. pollen, starch grains), nitrogen isotopes, the DNA of native and introduced species, and steroid biomarkers derived from humans, animals (faeces) and plants. Plant microfossils from surrounding soils will define the extent of cropping. Collectively, the analyses will enable bio-geochemical modeling to help predict the future of societies around the world where we are stressing carrying capacity of landscapes.
