“Rather than a case of abject failure,” the authors argue, “Rapa Nui is an unlikely story of success.” The islanders had migrated, perhaps accidentally, to a place with little water and “fundamentally unproductive” soil with “uniformly low” levels of phosphorus, an essential mineral for plant growth. To avoid the wind’s dehydrating effects, the newcomers circled their gardens with stone walls known as manavai. Today, the researchers discovered, abandoned manavai occupy about 6.4 square miles, a tenth of the island’s total surface.
More impressive still, about half of the island is covered by “lithic mulching,” in which the islanders scattered broken stone over the fields. The uneven surface creates more turbulent airflow, reducing daytime surface temperatures and warming fields at night. And shattering the rocks exposes “fresh, unweathered surfaces, thus releasing mineral nutrients held within the rock.” Only lithic mulching produced enough nutrients—just barely—to make Rapa Nui’s terrible soil cultivable. Breaking and moving vast amounts of stone, the islanders had engineered an entirely new, more productive landscape.
Mann sums up:
People have done lots of environmentally destructive things, heaven knows. But there are surprisingly few cases in which societies have permanently laid waste to their own subsistence. The history of Easter Island suggests that humans generally do have a long-term capacity to work with natural systems, even in extreme cases.
I just bought the Easter Island book, Mann’s new book, which I devoured immediately, is out soon.