Saturday, August 24, 2013

What does my daughter think?

My daughter, Sage, is almost 7. She enjoyed the recent article on Rapa Nui in the National Geographic Kids magazine (August 2013). The article was mainly about moai, and featured a link to video showing different ways some archaeologists think moai may have been moved.


But Sage seemed a bit disappointed. Earlier I'd shown her another set of videos (watch at least the first 2). Those videos present an clever alternative proposal by a Japanese engineer. Perhaps at least the smaller ones moved the way he shows! And some must have fallen over too?! One thing Sage and I agreed on is that the moai walking down the ramp might have been a great form of entertainment. Getting ready for and watching, and then talking about that sort of show might have kept us entertained for many years, if we'd lived on Rapa Nui.

Archaeologists may be the best people to test theories of moai movement, but I'd like to see more bright kids and engineers proposing ways for the archaeologists to test!

As I keep saying, many mysteries remain about moai, but these may not be central to understanding if people ran out of food. On the other hand, many estimates of population have been derived from how many people must have been needed to carve and move moai. But there's a problem – we don't know how moai were moved!

If I were writing something for today's kids, I might or might not start with feeding the moai movers. But I'd point out that the people must have had some great gardens and some great feasts around their umu (earth ovens). Food is something everyone can participate in!

Living here in Windy Wellington, Sage is very interested in the idea that the people of Rapa Nui may have warmed and protected their gardens with stones!

Taro (a Polynesian root crop) growing in the school garden on Rapa Nui.

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!

Tuesday, August 20, 2013

Gardens - Friday 16 August 2013


We've now finished our fieldwork! Time to pack up and think.

Reflecting on the week, and discussions on the island, I'd like to talk about Polynesian agriculture. Agriculture perhaps doesn't compete very well with the mysteries of moai for attention. But every story of moai has to feature how successful agriculture must have been to allow all those people to focus so much labour on building and moving moai. Let's focus on agriculture. Everyone loves a good garden!

The story of collapsing agriculture and soil erosion on Rapa Nui appears to be greatly exaggerated. A recent book by New Zealander Rhys Richards provides abundant evidence from previously unknown ship's logs (in maritime museums around the world) that agriculture remained highly successful on the island up through the period around 1864 when the island's population was decimated by disease. Abundant crops from healthy and extensive gardens were usually available for trade. An extensive 1864 letter from the first European missionary on the island, Eugenio Eyraud, emphasises that plants grew almost effortlessly, especially kumara (sweet potato). 

The key to agriculture, with crops coming from the humid tropics to relatively cool and dry subtropics was to maintain soil warmth and stop water loss. The cool temperatures we experienced this week (average daily high 22°C or 71°F) emphasise that Rapa Nui is cool in winter! Stones provide the perfect means to soak up heat, and also stop water loss from soil.

Since our last visit, there has been a lot of experimenting and demonstration of rock gardens, including mana vai and lithic mulch. Sonia took us to some gardens she created at the local high school, and along one of the main roads. All were impressive. 

A tiny taro plant, emerging from rocks.
Most impressive of all was the story of paired plots of taro. Taro is a root crop from the lily family, with leaves that grow as tall as a person when it is healthy. One plot was grown without stone mulch, and the other plot with stone mulch. After a year, both were harvested by the Earthwatch volunteers. The stone crop was much bigger, juicier, and healthier. Quantitative results, including nutrition testing, are part of the project.

I'm impressed with the emerging story of gardening. Most of all, the use of rocks and written evidence of health agriculture should make us all question the exaggerated stories of soil erosion that supposedly led to collapse after deforestation.


A variety of kumara (sweet potato) from Tahiti, growing in the school garden.

Bananas in a mana vai (enclosed rock garden).

Monday, August 19, 2013

Manu - Thursday 15 August 2013


Manu is the word for bird in Rapa Nui, just as is it in Maori. Prior to Polynesian arrival, Rapa Nui appears to have hosted a huge population of nesting seabirds since the volcano first emerged millions of years ago. For Polynesians, the nesting sites meant easy prey, so the nutrient inputs from guano died away with the birds.

So far, our soil N isotope results show that the N derived from seabird guano has persisted in agricultural soils more than I would have expected. We also planned to use the steroid signature of seabird guano to identify the time in our cores and soils when humans occupied the landscape. But the published signature of seabirds from North America and Australia hasn't matched what we're seeing in steroid samples run so far. Today, we're getting samples to help us establish a steroid and N isotope signature for seabirds.

We're getting some local guano from Rapa Nui. The frigate bird is typical of the seabirds that would have been present, so we sampled a number of individual guano piles beneath perches.

Sonia arranged for Sebastian Yancovic Pakarati, a Rapa Nui who has recently returned to the island to run an ecotourism business and starting a bird conservation project (The Manu Project), to take us to good site. The site is easier for us to get to than smaller islands with nesting sites. The trip was also very enjoyable because we went to the one part of the island where we haven't had a chance to go - Poike, the oldest and most eroded volcano. Sebastian, with his previous experience as a mountaineering guide in Patagonia, proved excellent at knowing a safe way to descend the sea cliff to frigate bird's spectacular perching sites.

Thanks Sebastian!


Sebastian Yancovic Pakarati, atop the sea cliff we descended to access perching sites.
Sebastian helps collect guano from a spectacular site.
We collected from a number of individual piles of guano beneath perches - hopefully provided a range of independent samples.

Sunday, August 18, 2013

Help From Our Host! (Wednesday 14 August 2013)

Today was a day off of field work. Our biggest goal was reporting some of our findings to CONAF – the agency that manages the Natioanal Park. The biggest challenge was that most of the staff don't speak much English and our Spanish is nearly non-existent. It went remarkably well, with our host, Sonia Haoa (pictured below) serving as translator. We gave presentations and tried to tell as much of the story as we could with pictures. The language barrier forced us to keep the messages simple, but some questions proved complex to answer. They seemed entertained when the questions about the ant dating got so complex Mark and I couldn't agree between ourselves anymore!
Sonia Haoa discusses reconstructed Polynesian gardens.

The language barrier makes it difficult for us to fulfil one important ethical responsibility of doing research in a place like Rapa Nui – reporting our findings back to the people on the island, particularly the native Rapa Nui population. It seems some researchers haven't felt this is a responsibility, or communicated enough, and therefore there is tension. We feel this tension most when we arrive and need to obtain permission to collect samples. This is made more complicated by the multiple institutions responsible for granting permission to conduct research. We're lucky that CONAF has stepped forward to coordinate the process for us, and link it to the permission that was already granted 4 years ago. The system of permissions has changed, probably for the better, but remains very confusing to me. It is much easier because we are not doing archaeology, which has a much higher bar for gaining permission. Regardless, it is always very helpful to have a lead agency!

The permission system, and the lack of clarity isn't just stressful for us. It puts a lot of pressure on our host, Sonia. As a Rapa Nui, who began working with Thor Heyerdahl at the beginning of her research career, Sonia is one of the most knowledgable and committed researchers on the island. Unlike the many researchers focused on moai, she is firmly committed to understanding the island's agricultural history. We are enormously indebted to Sonia, and lucky to work with her. Last time, her team was of great help. This time, she's been doing most of the work herself.

Sonia - Thanks! Muchas Gracias! Maruru!

Friday, August 16, 2013

The Nature of Evidence - Tuesday 13 August 2013

Yesterday afternoon, we tackled our first piece of field work. The reasons for this piece of work take a bit of explanation. As a word of warning, this blog post therefore will have some science detail. 

We're to trying to understand confusing evidence from our longest Rano Kau core. With the help of Maureen Marra, we recovered a few ant fossils in our core. We assumed the presence of the particular ants we found meant that the ant species were transported across the Pacific by Polynesians. Most were at the depth in the core we were convinced represented Polynesian arrival. So we radiocarbon dated the tiny ant fossils. But, the results suggested the ants were roughly 3000 years old, much older than the expected age of 800 years.

One could possibly argue that Polynesians must have transported the ants and arrived 3000 years ago, but this would seem to contradict many decades of careful archaeological work. Before we start to accept a new claim, the process of science requires us to try to disprove the hypothesis representing this claim. One of the most logical explanations for the 3000 year old ants is that the ants were eating 'old' carbon. This would undermine the hypothesis of ants arriving 3000 years ago.
Most of you may need a refresher on how radiocarbon dating works. Radiocarbon is produced in the atmosphere by cosmic rays, establishing a fairly uniform amount of radiocarbon in atmospheric carbon dioxide. Radiocarbon dating works by measuring the radioactive decay that has occurs since the atmospheric carbon dioxide has been taken up and used to build plants.  Subsequently, animals who eat the plants may also be dated.  If an animal, such as one of our ants, eats carbon that was taken from the atmosphere a long time ago, its age will appear much older than expected. This commonly occurs with animals (or humans) eating a seafood diet, since the surface ocean holds dissolved carbon dioxide for hundreds of years.

We descended into Rano Kau crater and laid out some lures to collect ants similar to those we found in our cores. We collected ants at three levels - the crater rim, slope and edge of the lake. We found the most ants at the edge of the lake where it was moist (pictured), and few at both the midslope and crater rim (where Mark is pictured).

Do you think our ants will have radiocarbon ages that make them look thousands of years old? If they do, then the age of the ants can be treated as bad luck and discarded. If that's the case, then the presence of ants in the core can be interpreted as evidence of Polynesian arrival. Or, if the ants we collected look like today's atmosphere, maybe we do have very unexpected evidence of Polynesians reaching Rapa Nui but not settling long enough to leave archaeological evidence?

Do you prefer the idea of the now agreed time of arrival (1200AD), or a so-called 'early arrival' (3000 years ago)? For years, archaeologists and paleobotanists have argued for and against 'early arrival' theories, and the ability to clarify the evidence has been greatly improved by our ability to use accelerator mass spectrometry to count radiocarbon atoms (requiring samples of a milligram or less). This has made it much more feasible to date short lived seeds, twigs, leaves and other materials that are not from big, old trees (like charcoal) or from the sea (like shells). Previously, dating by radioactive decay counting required much larger samples - many grams of material.

Hopefully, the evidence will be clear after we 'date' the ants we have collected.

Thursday, August 15, 2013

What does it feel like to be back? (Monday 12 August 2013)

We were last here in April 2009. What's changed?

Much is the same, but rapid economic development is definitely continuing on Rapa Nui. Some aspects are good; others might be considered not so good. And some things really haven't changed.

It's a different time of year (mid-'winter'), so it is cooler, wetter and greener. Flowers seemed to be omnipresent before, but there are even more now. Pictured here is the small but brilliant flower of guava - an introduced scrub tree that covers the island like a woody weed. At least it is both pretty and produces tasty fruit.

Looking beyond the different flowers, the most obvious change is that even though there were a lot of cars before (1 car per 1.8 people according to one source I quoted in my blog), there are even more cars now. They are bigger, newer, nicer and there are more utes/pickups. Before, light Suzuki 4wd SUVs were most common, but this is no longer the case and I wonder where they all went!

Speaking of  transportation, an interesting point I brought up in 2009 was that the police were trying to enforce a helmet law on scooters and motorbikes. Though many tourists wear helmets, when I look at the locals, it is now quite apparent they've given up!

Despite the increase in automobiles, and investment in hotels, and a few new houses, the standard of typical buildings - particularly along the main street - has not changed. I'm told that the reason is very similar to something that affect Maori land in New Zealand. The land is indigenous land. Land owners cannot get mortgages, because the bank can't take the property if they fail to pay back the loan. So without bank loans, investment is limited to surplus cash on hand. In many cases, tourism is providing enough cash for new building. In other cases, there's creative use of cheap materials that are available, which is neat to see when it is done well. My favorites are the artistic flare, and when natural shapes of native wood are incorporated in buildings. The building pictured here is constructed of cheap materials - but adorned with fresh painted art representing the island's cultural heritage.