Unraveling the Mystery of Easter Island

So my last post was about rats and the role they may have played in deforestation on Easter Island. As you may have noticed, a great deal of the rat debate comes from the archaeologists Terry Hunt and Carl Lipo, (who I think I take far too much information from!). Upon searching the news for stories related to Easter Island I came across this blog entry on the courier-journal.com, reviewing one of Hunt and Lipo's latest books "The Statues that Walked: Unraveling the Mystery of Easter Island," written in 2011. As Peter Smith at the courier-journal reviews, the book goes into great detail looking at the entire Easter Island story, reviewing (and rejecting) evidence for the traditional explanation (ecocide) and instead suggesting that rats drove deforestation the island and that contact with Europeans led to the island's ultimate collapse.

Mr. Smith makes a closing point which I think is very important: assuming ecocide was not the cause for the collapse on Easter, the alternative story still offers lessons: "Live within your means. Watch out for invasive species. And especially invasive people," (Courier-journal.com 2012). The impact invasive species can have on ecosystems, as I have discussed, can be potentially catastrophic, so if we can't learn a lesson about human driven environmental degradation from Easter, we can certainly be more cautious about this one. Especially as humans have time and time again ruined the biodiversity of numerous ecosystems by introducing outside species into them - e.g. introduction of the Nile Perch into Lake Victoria in 1955 devastated native fish populations. Anyway, I highly recommend both Hunt and Lipo's book and the courier-journal.com, which seems to offer news and posts related to almost anything I can think of let alone Easter Island! 

A rat race?

As my earlier posts have discussed it is likely that deforestation was driven by a number of factors. I touched upon the role that rats may have played in this post but now I will go into a bit more detail about them. Hunt and Lipo (2009) write that there is an extensive literature documenting the profound impact rats have had on the vegetation and ecosystems of a number of islands across the Pacific. Although, Diamond pointed out (2005) that while on some islands rats have had catastrophic effects, on others they have made no apparent impact, showing that although there is potential for rats to be damaging to island ecosystems they aren’t necessarily the cause in every case. 

Andreas and Bork write (2010) that it was common for Polynesian settlers to bring rats with them to an island as a valuable source of protein, and indeed on Easter numerous rat bones were found in archaeological excavations and often in cooking pits. Rat bones on the island have been dated to first appear as back as between 600AD and 1260AD (Andreas &Bork 2010), showing that they were around long enough ago to potentially have played a role in the greatest period of deforestation between 1200AD and 1650AD (Hunt & Lipo 2009).

If you remember from one of my previous posts, the island had a particularly fragile environment, especially to invasive species due to the relatively small biodiversity and lack of predators (Hunt 2007). Rat populations therefore could have grown very rapidly on the island, and as palm nuts were a primary food source (Sardar 2008) it is likely they would have had some sort of destructive impact on the forests, as was seen on numerous Hawaiian islands (Hunt 2007).

Hunt (2007:496) Shows decline of rat population between early and late period – rat populations dependent on forest resources?

However, as Hunt (2007) comments, the relative contribution of rats to deforestation remains poorly understood, although a large amount of palm nuts have been discovered gnawed. Andreas and Bork (2010) add that numerous pieces of evidence suggest that rats were not responsible for deforestation. Firstly, rats are unable to kill mature trees, making palms fully grown by the 13^th to the 15^th century able to survive till the first European contact due to their relatively long lifetime, suggesting a number would have indeed been cut down. Furthermore, numerous palm stump relicts have been found, as well as widespread ash and carbon layers to show that fires had burned over extensive areas of the island (Andreas & Bork2010).

Despite this, I believe writers like Hunt & Lipo are more suggesting that rats played a role of relative importance, rather than an all or nothing factor. Although it seems unlikely rats could have been the sole cause for deforestation, the evidence suggests that they must have played a significant part. Rat populations could have grown almost completely unhindered on the island and as palm nuts were their primary resource, it is likely this growth would have been reflected by forest destruction. Indeed, the greatest period of deforestation appears to occur following the growth of rats on the island and as the forests declined so did rat populations.

The statues that walked?

Since my last post concluded that climate change probably wasn't the cause for the collapse on Easter, my following posts will be talking about other possible causes. Today however, I thought I would just share a very interesting video I came across on National Geographic's website that shows an alternative method of statue transportation to the classic story (using numerous logs to roll them).

The video shows a group of archaeologists moving statues down a path using just rope - and to be honest, if a group of pasty archaeologists can do it I'm fairly sure the hardened Polynesian's could have handled it easily enough as well! If the Easter Islanders did in fact move their statues using just rope, this suggests the deforestation on the island wasn't a clear cut case of them cutting down all the trees to satisfy their need to construct statues. Therefore, it is likely something other than just the islanders played a part in the severe deforestation, but this is something I'll come onto in another post.

The Usual Suspect?

In my last post I discussed whether or not ecocide was the cause for the collapse of the society on Easter Island and as I concluded with a probable 'no' I'm now going to talk about what else could be to blame. Now, the title of this post doesn't refer to the mid 90s neo-noir film starring Kevin Spacey (although I highly recommend it), but instead I'm going to be talking about the common suspect behind environmental issues - climate change.

brrr! 

When I started reading around to understand the argument behind climate change as the cause for deforestation on Easter Island, two issues came up repeatedly - that there is no direct information about climate change on Easter, especially between AD1000-1700 (Diamond 2005, 2007, Mann et. al. 2008) and that Easter's forests survived tens of thousands of years of climatic fluctuations since the Pleistocene (Diamond 2007, Hunt 2007).

These two issues therefore already make the case for climate change a tough one but two articles I read argue the case in spite of this. Mann et. al. (2008) argue that although palaeoenvironmental history of Easter is very poor, some hypotheses can be made. One interesting argument is that latitudinal shifts in subtropical storm tracks could have resulted in changes in intensity and frequency of cyclonic storms in the Pacific in a way that would have deprived Easter of a great deal of rainfall (Mann et. al. 2008). Most of the rain on the island comes from cyclonic storms moving across the Pacific, but the track of these storms can shift depending on the temperature gradient between the pole and equator which varies on an annual, decadal and millenial time scale. It therefore could be that these shifts in storm tracks may have deprived Easter of rainfall that was already fairly low, leading to severe droughts on the island and thus driving deforestation. Although this is an interesting hypothesis, Mann et. al. agree that it is as yet untested.

Strenseth et. al. (2009) argue that periods of greatest deforestation (AD1250-1650) coincide with the most intense El Nino Southern Oscillation activity during the last millennia, suggesting that there could be some correlation. ENSO is known to directly or indirectly cause shifts in Sea Surface Temperatures which can lead to lower biomass production. As a result of this it is possible that the islanders may have put greater pressure on forest resources in order to either build larger canoes in order to reach other fishing grounds or to create more land for agriculture to cope with lower marine food resources (Strenseth et al. 2009). In a Hunt and Lipo paper (2009), evidence suggests this is an unlikely explanation as the palm trees that largely made up Easter's forests were not likely to be used for woods and marine food resources do not disappear from the faunal record at all, with sea mammal bones remaining present in even late pre-historic deposits (i.e. there was no decline in fishing that would have led to a resulting increase on land resources, at least to an extent that would push deforestation alone) (Hunt and Lipo 2009).

Added to the two issues I raised at the start of this post and the lack of convincing arguments elsewhere, I do not think climate change played a hugely significant role in deforestation on the island, although as Cole and Flenley (2007) comment, it is likely forest vegetation recovery may have been constrained by droughts at times, I do not think that any specific climatic events caused it's downfall.

Easter Island – ecocide?

Easter Island is widely referred to as a classic case of ecocide “where the ancient Polynesians recklessly destroyed their environment and, as a consequence, suffered collapse” (Hunt & Lipo 2009:601). In this post, as Jo rightly mentions (who, by the way has a great blog about societal collapse of the Norse in Greenland – here), I will be examining how accurate this is – to what extent was the collapse of the Easter Island society a result of ecocide?

As I established in previous posts, Easter supported a subtropical tall forest and a range of food resources from shellfish to land birds (Diamond2005, Hunt 2007). However, the island was also a relatively fragile and vulnerable environment, with quite poor soil subject to strong winds and highly variable rainfall (Hunt & Lipo 2009). It is therefore no surprise that the arrival and growth of human populations on such a small and isolated island led to the depletion of these resources and the degradation of the environment as a whole.

On the surface the widely known image of collapse on Easter as a case of ecocide seems likely. Early research puts the blame largely on the shoulders of the Polynesians, the French explorer La Perouse commented in 1786 that the islanders “were indebted to the imprudence of their ancestors for their present unfortunate situation” (1789:318-319 in Hunt and Lipo 2009:602). The common explanation being that as population grew, more forest was cut down for agriculture, fuel and statue building and at a rate faster than it could regenerate (Diamond 2005).

Although this seems plausible, recent research casts doubt on this version of events. Although to summarise all the research against this case would be beyond the scope of this meagre blog, I will discuss a couple of issues raised in recent papers.

Hunt (2007:485) argues that “prehistoric deforestation did not cause population collapse,” using numerous observations to illustrate his argument. One major issue is that all palaeo-environmental evidence used in papers discussing the conventional story has questionable reliability and validity, with error margins often between 100 to 200 years (Hunt 2007). In this paper Hunt stresses that humans were not the sole driver of deforestation and points to the huge impact rats would have had. As a small, closed ecosystem Easter would have had little biodiversity and few, if any predators, making invasive species hugely threatening (Hunt 2007).

Documented rat population growth rates on other Pacific islands suggest rats could have grown into huge numbers in a very short space of time on Easter. Many other Pacific and Hawaiian islands have seen severe deforestation resulting solely from rats, as they use tree nuts as a primary food resource, thus preventing tree populations from regenerating (Hunt 2007). Hunt argues the relative contribution of rats to deforestation remains poorly understood and that is highly likely that both a combination of humans and rats, and indeed other factors, would have driven deforestation.

Doesn't seem so bad does he?

Hunt and Lipo (2009) make a number of points, but one argument that struck me was that the period of greatest deforestation occurs between AD 1200 and 1650, a period where population actually rose, with the only sustained decline of population occurring between AD1750 and 1800, after the arrival of European visitors (Hunt & Lipo 2009).

Source: Hunt T.L. and Lipo C.P. (2009:609)
Obsidian hydration dates used to infer population - obsidian used to make tools, weapons etc.
Population rises between 1200-1650, only sustained drop post European contact (downward arrow)

In both papers (Hunt 2007, Hunt & Lipo 2009) the sharp population decline on the island is framed as resulting largely from contact with Europeans, due to disease and slavery, with conventional arguments being based on speculation about prehistoric population size and unreliable palaeo-environmental records. Even in Diamond’s book Collapse (2005) this issue is clear, as many conclusions are drawn from evidence on the Poike Peninsula which are then extrapolated to the entire island (Diamond 2005). This is an important issue as Poike is in fact relatively peculiar in that is one of the few places on the island not covered in bedrock outcrops (Hunt & Lipo 2009) and therefore an unreliable analogue for the rest of Easter.

I therefore think that the collapse on Easter is not a clear cut case of ecocide, as records show that there was not a solid trend of deforestation matching population decline and that the largest periods of population decline occur after contact with Europeans. Furthermore, humans were likely not the only cause of the environmental degradation, as mentioned earlier the soil on the island was poor to begin with and as Hunt (2007) shows, other factors such as rats would have had a huge impact. I will go into alternatives in more detail in later posts, but it is clear that the conventional story is not completely sound.

A bit of geography!

As I will be talking about Easter Island in the following blog posts, I suppose it is necessary, as a Geographer, to give an overview of the island's geography.

Easter Island, as mentioned previously, is a very remote island located in the south eastern Pacific Ocean many thousands of miles from any other landmasses (2300 miles from Chile, 1300 miles from Pitcairn Island) (Diamond 2005). The island is located at a latitude of 27 degrees south in the subtropics. This subtropical location gives it a mild climate but interestingly as all other Polynesian settlements lay much closer to the equator, Easter is relatively cool in comparison. The weather on the climate involves relatively strong winds but a very small amount of rainfall at around just 50 inches per year (Diamond 2005). This rainfall percolates very quickly into the soil of the island due to it's volcanic nature, cutting down freshwater supplies significantly, as shown by the island's one intermittent stream (Flenley and Bahn 2003).

Easter Island - Middle of nowhere!

Why is this important?

Even if you didn't ask, I feel like I should probably tell you anyway. The isolation of the island made life difficult for the islanders in two important ways. Not only did it make communication with other Polynesian colonies difficult but it also made it relatively deficient in biota:

• Flenley (1993) reports only 48 plant taxa for the island, fourteen of which were introduced by Polynesians 
• Few if any indigenous terrestrial vertebrates with just two lizard species being native to the island (Klemmer and Zizka, 1993 cited in Hunt 2007)
• Steadman et. al. (1994 cited in Hunt 2007) report just 25 seabird species 
• Diamond (2005) documents just 127 species of fish compared to over 1000 species at Fiji 

Similarly, the subtropical location of the island brings a lot of negatives for the colonists. As all other Polynesian colonies were far closer to the equator, many crops they brought over to Easter grew poorly there, such as coconuts (Diamond 2005) or breadfruits (Hunt 2007). Furthermore, this cooler climate meant the ocean surrounding the island could not support coral reefs as other Polynesian islands could, greatly reducing the amount of fish and shellfish available to them. 

Finally, the relatively low amount of rainfall has obvious implications, as the islanders would have had to put a considerable amount of effort into obtaining freshwater with such a limited supply. As Hunt (2007:486) comments, not only was the rainfall limited but it could also "fluctuate dramatically" and "serious droughts could have been a significant problem" due to the low rainfall and excessive drainage of Easter's soils. Additionally, strong and salty winds would have had a devastating impact on agriculture (Hunt 2007) as well as causing breadfruits that could grow to drop before they were ripe (Diamond 2005).

From this overview we can see that the Polynesians that settled on Easter would have had a comparatively hard time surviving there than on many of the other islands in the south Pacific. Not only were resources relatively limited, the weather was against them, they had little ability to remain in contact with other islands and many crops and foods they brought to the island were ill suited to it's climate. However it is clear, purely by the fact that the islanders were around for many hundreds of years to follow, that they could adapt to these problems - to an extent, at least.