Wednesday, August 21, 2013

Carry capacity - Saturday 17 August 2013

Today is our departure - back to New Zealand.

The week of sampling and discussions makes my mind spin on many topics. There always seem to be interesting researchers passing through, doing research or sometimes leading tours. We only have had this one project here, yet many of the people we meet have spent much of their research career working on Rapa Nui. This leads to very interesting discussions.

A view of one of the large areas where population potentially thrived on Rapa Nui. Could it have exceeded agricultural carry capacity?
While departing, the big question on my mind is about the ultimate question: was there a "collapse"? There's very little (if any) hard evidence. Certainly the statue-building culture came to an end, but did population crash or collapse too? There's a real risk that we won't have any clearly dated section of sediment core that allow us to achieve our goal of measuring fertility and relatively population size during that critical timeframe around 1600 AD.

That's plan A. Our plan B has always been to reconstruct the nutrient budgets of the agricultural systems. Then we can determine if they could support a large population through climate extremes, particularly drought, even as nutrients declined from peak pre-deforestation levels. This allows us to better understand the carrying capacity of the island.

Did the people there exceed the limits of the their environment? Understanding how environment places limits on society and economies has become a major focus of environmental science recently, with serious arguments about how multiple limits can be calculated. Can Rapa Nui's past help us shed light on this debate? Are there boundaries or limits that must not be crossed?

This trip has helped us understand the details need to calculate how much food can be produced in an area like the one shown in the photo above. This photo shows the view looking west from Poike. The best beach for landing ocean going canoes is off the farm to the right, and the statue building area at Rano Raraku is off to the left. It looks rocky, and it is. But maybe those rocks protected the soils and plants, and indicate occupied structures, much more than we would have ever thought!

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