An Easy Guide to the Theories of Easter's Collapse

So now we have looked at all of proposed theories of collapse on Easter Island. I have created a table which summarises all of the causes of collapse, how they could have caused Easter’s collapse, the lines of archaeological and palaeological evidence that support each theory and the sources and articles I have used in my posts to investigate their impact on Easter Island….hopefully it will make things a little bit clearer for everyone.

So from looking at all these causes, what can today’s society learn from Easter Island? The next few posts will investigate some of the ways that our society today can look at the mystery of Easter Island and learn something from them, no matter whether they collapsed due to murder or suicide.

Europeans and Easter

“This story of self-induced eco-disaster and consequent self-destruction of a Polynesian island society continues to provide the easy and uncomplicated shorthand for explaining the so-called cultural devolution of Rapa Nui society”

(Rainbird, 2002)

The ‘ecocide’ theory is not the only solution to the Easter Island mystery. Numerous other scholars advocate that the arrival of Europeans and slave traders were the reason behind Easter’s collapse. Benny Peiser (2005) in his paper ‘From Genocide to Ecocide: The Rape of Rapa Nui’ claims that Rapa’s culture and environment were destroyed to all intents and purposes by European slave-traders, whalers and colonists, and not by themselves.

Between the first European contact in 1722 and the beginning of Peruvian slave raids in 1862, it is estimated that 53 European vessels called at Easter Island (Peiser 2005). During this time, the Europeans brought foreign diseases to Easter, particularly smallpox and other Old World diseases. As well as diseases, Benny Peiser paints a gruesome picture of violent assaults, murder, rape and mass deportation of the native people by early European visitors, whalers and slave-raids. Slave-raids first started on Easter Island as early as 1805, however from October 1862 to March 1863 an estimated 1000-1400 people were captured and deported by Peruvian and Spanish slave-raiders. Peiser claims that almost 90% died in the following weeks due to disease and malnutrition (yet provides no evidence to support this claim).

With the deportation and deaths of many within the native population, including tribal and community leaders, the social and religious system disintegrated, leading to internal strife and tribal fighting. It is this fighting, combined with the deaths and deportation of 1000-1400 people that Peiser argues was the cause of societal collapse and starvation. He maintains that there is no reason to believe that Easter’s civilization could not have adapted and survived to an environment devoid of large timber, however what they could not have adapted and survived was the ‘systematic destruction of their society, their people and their culture’. Essentially, it wasn’t suicide by the native people themselves, but rather genocide by whalers, colonists and slave-raiders.  He concludes with a quote from Rainbird (2002):

‘Whatever may have happened in the past on Easter Island, whatever they did to their island themselves, it totally pales in insignificance compared to the impact that was going to come through Western contact’

However, there are a couple points on Peiser’s article that I would like to draw attention to:

1. He spends the majority of his article picking apart Diamond’s ‘ecocide’ theory, claiming that it is not the real cause behind Easter’s collapse. His main line of argument to support this is that Diamond has very little archaeological and palaeological evidence, with statements like ‘Diamond’s methodological approach suffers from a manifest lack of scientific scrutiny. Instead of weighing up and critically assessing the quality, authenticity and reliability of the data he employs to support his arguments, he consistently selects only data and interpretations that seem to confirm his conviction that Easter Island self-destructed.’ This claim is not new (many scholars have questioned Diamond’s lack of evidence), however Peiser seems to do exactly the same as Diamond later on in his article as he uses no scientific evidence to prove his assertion that Western contact was the cause of Easter’s collapse, and makes statements such as ‘It is believed (but by no means certain) that almost 90% died in the following weeks and months of diseases and malnutrition’. Essentially (in my opinion), he seems determined to pick apart Diamond’s theory, before collecting solid scientific evidence to prove his theory.
2. He states that Easter’s population collapse occurred in 1864, however Roggeveen’s observations from 1722 suggested that Easter’s collapse had already happened by the time he arrived, and this is supported by numerous lines of scientific evidence (Flenley and Bahn 2003)

However, Hunt and Lipo (2007, 2009) provide a more solid argument backed by evidence for Western contact as the cause of collapse. They argue that demographic collapse likely began as a consequence of Old World diseases, rather than the murder, rape and mass deportation that Peiser maintains (however, these did still have some impact on Easter’s population). The first wave of epidemics occurred with the arrival of the Dutch in 1722, then with the Spanish in 1770 and the English in 1774. Slave trading, more epidemics and other devastating blows from colonialism then hit the population. However, they contest the arguments made by Flenley and Bahn, and Diamond that Easter’s population collapsed pre-European arrival, simply stating that there is no existing evidence for a pre-European contact population collapse, and that a per-contact demographic collapse remains untested and undemonstrated archaeologically. Rather, the impact of historic slave trading, epidemic diseases, intensive sheep ranching and tragic population collapse has been recognized for a long time.

It is clear from this to see two very opposing sides to the Easter Island mystery with respect to Western contact. While one side argues that there is much evidence for pre-contact population collapse (Diamond, Flenley and Bahn), the other side argues there is no evidence for pre-contact collapse (Rainbird, Peiser, Hunt and Lipo), the quality of archaeological and palaeological evidence on Easter Island is not of good enough quality to prove either argument. European arrival on Easter Island had a clear impact on the population of Easter, however the argument is whether the population was already in decline as a result of population expansion, deforestation and resource exploitation. 

Cannibalism and Civil War

According to Diamond’s theory, as deforestation, resource exploitation and population expansion began to ‘destroy’ Rapa Nui, the Islanders descended into warfare and cannibalism. This has captured the attention of the public, as can been seen in the movie ‘Rapa Nui’ (see previous post), which bases its story around civil war on Easter Island.

BBC’s horizon created a documentary on Easter Island (again, see my previous post), but can be summarised in this article (http://www.bbc.co.uk/science/horizon/2003/easterisland.shtml). Evidence of civil war can be summed up into these points:

• Archaeological evidence include wooden carvings of emaciated people and the appearance of weapons, such as spear tips
• Skeletons have been found with severe wounds (Flenley and Bahn 2007)
• Changes in diet coincide with civil war. Resources were scattered around the island, yet friendly trade on the island allowed all tribes to survive – once they were at war with each other, friendly trade disappeared
• Legends talk of a time of hardship, terror and cannibalism

Diamond claims that three-quarters of the human population died out due to cannibalism, starvation and civil war, and that one of the world’s most remarkable civilisations self-destructed. The last point encapsulates the theory that Easter Island descended into warfare and cannibalism…it is simply a legend and myth. It is plain to see from these points that very little evidence exists to support warfare and cannibalism on Easter Island. The texts from the Dutch expedition in 1722 report fields of yam, and healthy, fit people, which contradicts a violent cannibalistic society suggested by Diamond (1995):

‘They also turned to the largest remaining meat source available: humans, whose bones became common in late Easter Island garbage heaps. Oral traditions of the islanders are rife with cannibalism; the most inflammatory taunt that could be snarled at an enemy was “The flesh of your mother sticks between my teeth.” ‘

Most scholars researching Easter concur that this theory is no more than a hoax designed to capture the imagination of the public, and has very little archaeological evidence to support it:

• Hunt and Lipo (2007) analysed spear heads that were supposedly used for weapons, and concluded that very few of the hundreds they inspected possessed the traits that would make them good weapons
• Based on a study of 2618 bones, Owsley (1994) deduced that 2.5% of them showed signs of traumatic injuries
• NO evidence has actually been found for cannibalism

To conclude, Bahn (1997) claims this theory as:

‘One of the most ridiculous yarns ever spun about the island’

References

Owsley, D. W., Gill, G. and Ousley, S.D. (1994) ‘Biological effects of European contact on Easter Island’ In. Larsen, C.S. and Milner, G.R. (eds) The Wake of Contact: Biological Responses to Conquest 161-1 77. New York: Wiley-Liss, Inc.

Bahn, P.G. (1997) ‘Easter Island or (Man-) Eaters Island?’ Rapa Nui Journal 11(3): 123-125.

Resources on Rapa

Resource exploitation is clearly a potential cause for the collapse of Easter Island, and it is supported by Diamond’s “ecocide” theory and those who follow a similar view to him. Resource overexploitation started with the Jubaea chilensis palm deforestation, which then triggered the overexploitation of a whole host of resources. Meith and Bork (2005) analyse the soil profile on Poike peninsula to prove that soil erosion was a contributing factor to Easter’s collapse, whereby poor soil fertility (caused by deforestation) halted agriculture, thus depleting resources produced from farming. 

Easter Island’s isolation combined with the population expansion suggested by Bologna and Flores (2008) triggered resource exploitation, exceeding Easter Island’s capacity. Population and deforestation of the Jubaea chilensis palm caused the overexploitation of the resources provided by the palm, for example firewood, building materials for houses, roof thatching, food from the palm nuts, hunting material and canoes for fishing offshore. Diamond (2005) suggests that although Roggeveen found no animals bigger that insects when he arrived on the island, however Diamond (2005) claims that Easter once had the richest seabird-breeding site in Polynesia, once being home to porpoises, turtles, fish, shellfish, rats, seals and large lizards. This clearly advocates resource exploitation, however Diamond provides no evidence to support this point.

Croix and Dottori (2008) implement a model that reconstructs the population, economy and resources on Easter Island. It pretty much summarises resource exploitation as a cause of Easter Island collapse, showing the decrease of forest resources from the reconstruction of forest pollen and corresponding increase in soil erosion (from % Loss on Ignition), which triggered a decrease in agricultural resources. It also illustrates evidence from charcoal particles that were used to reconstruct population increases, which is a trigger for resource overexploitation. The figure below represents the model results from this study.

However, Rainbird (2002) has challenged the view that resource degradation was the principle cause of the collapse of the Easter Island economy and society. Although Rainbird acknowledges that extensive environmental degradation may have occurred on other resource-poor and relatively small Pacific Islands, instead he maintains that contact with the “material culture” and “diseases” brought by Europeans was the more likely source of the demise of Easter Island. Hunt and Lipo (2007) also challenge this view, suggesting alternative theories (some already covered in this blog) such as rats causing deforestation, the capture of Islanders for slave trade and the arrival of Europeans brought diseases that the Islanders were not immune to. The impact of the arrival of the Europeans and their disease will be analysed in the next post.

References

Diamond, J. (2005) Collapse: How Societies Choose to Fail or Survive London: Allen Lane

Kevin Costner and Easter Island?!

The Easter Island mystery is so intriguing, that a film has been made about it. Produced by Kevin Costner, the film ‘Rapa Nui’ tells the story of civil war between the ‘short eared’ and ‘long eared’ tribes on Rapa Nui (Easter Island), and the fight between two opposing leaders of these tribes for the love and affection of one girl. In terms of geography and anthropology, you do have to take this film with a pinch of salt, as factually it is most certainly not perfect! I may be in danger here of turning into a movie critic, but by investigating the parts of this film that are factually inaccurate, we can actually highlight and learn some things about Easter Island.

For example, this film is set 300 years ago (around AD 1700), and tells how there is civil war between tribes on the Island. The tribes are still erecting statues, however, it is impossible for these tribes to be erecting the moai when they are at war. As has been highlighted in a previous post, resources were scattered around the island, with stones for the moai in the, quarries for the red stones that formed hats for the moai, fishing in the, agriculture in the, and forests in the. This suggests not only a complex and highly organised society on Easter Island, it also suggests that friendly trade between tribes that congregated round the resources must have been in place for the statues to have been built. Thus statue building and civil war could not have coincided. Basically the film seems to have mixed two eras into one!

Secondly, the film assumes that the islanders cut down the palm trees for space for the moai. Although this could have been possible, it is much more likely that the trees were cut down, if they were cut down at all, to provide resources and to make space for agriculture rather than the statues.

The film advocates the popularised view shared by Jared Diamond that Easter Island collapsed due to the ‘ecocide’ theory. The influence of both the film and Diamond’s books are dangerous for Easter Island as causes people to form a preconceived view on why Easter collapsed, without looking at the different theories of collapse. 

Easter Island Apocalypse: Population Expansion?

So, what has happened to the point I made in my very first post about Easter Island being a parable to today’s society? Well today’s post will look into just this. Already we can see the potential impacts deforestation had on Easter Island (depending on whether you support Jared Diamond’s theory, or Hunt and Lipo’s theories), yet the underlying cause of deforestation, as proposed by Diamond, is population expansion.

It may (and should) be clear by now that the theories behind Easter’s collapse are highly contested. Population expansion, as suggested by Jared Diamond and many other scholars COULD be a cause behind Easter Island’s demise, but it should be obvious that t his is only one side to the argument. Theories already discussed, such as the rat theory, and theories to come, for example, the arrival of the Europeans and slave trade are also supported by archaeological and anthropological evidence, and are no less important. I am only saying this because it is easy to be caught up in the more popular idea that the Easter Islanders caused their own demise….’suicide’, without looking at all the arguments and evidence. That said, I will investigate a couple of papers that suggest population expansion was the cause behind the Easter Island collapse.

The Malthus prediction that:

‘Population growth would eventually lead to natural resource depletion, economic decline, starvation, violent conflict and population decline’

seems remarkably close to the Easter Island story suggested by Diamond.

Bologna and Flores (2008) implement a mathematic model that explains the rise and fall of Easter Island. The model considers the interaction between natural resources and population, and generates an estimation of the civilisation’s collapse time. The diagram below shows the model predicted population and amount of resources.

They predict a population increase to 7000 by AD 1400. This estimate is similar to those made by Bahn and Flenley (1992) from the pollen record, and by Diamond (2007) and Rainbird (2002). In addition, this peak population is also supported by the fact that moai construction peaked between 1100 and 1400 A.D. Moai construction indicates the presence of a large population since their construction requires intensive labour, and it also suggests a complex society that were able to organise such large-scale projects.

Bologna and Flores use their model to determine the civilisation’s equilibrium point where humans can coexist with the available natural resources indefinitely. They estimate the equilibrium population size to be around 2000 people, as it was around 1175. Meith and Bork (2005) suggest that sustainable agriculture existed up until A.D 1300, perhaps implying that humans and natural resources were in equilibrium. Considering the year 1175 falls into this phase of sustainable agriculture, Bologna and Flores’ predicted equilibrium population size seems entirely likely.

The model then shows a population decline to 2000 by 1600 A.D that coincides with a sharp drop in resources, as shown by the diagram.

However, Wolcott and Conrad (2011) advocate that using the interaction between humans and resources to drive the model is not accurate, and the influence of soil erosion must be factored into population estimates from mathematical modelling. Their research proposes that population decline occurred because soil erosion caused agriculture to fail, which can be seen in the diagram below.

Either way, both studies show the general trend that Malthus predicted, where population increased past the equilibrium population size, resources were depleted (with the help of soil erosion causing agricultural failure), causing population decline. Bologna and Flores conclude by stating:

‘The model could be, with the opportune changes, applied to the planet…of course there are many differences but surely the planet can be considered an isolated system as Easter Island was’

which sums up not only their view, but many other scholars as well. Of course, as I have already mentioned, this popular viewpoint is only one side of the story…there is much more to be discovered and told about Easter Island yet!

Easter and erosion: Could soil erosion have been a contributing factor?

Now that we’ve looked at the impacts of deforestation on Easter Island, its time to look into a couple of other causes, and whether or not they contributed to Easter’s demise. Using a study by Meith and Bork (2005) in their paper, ‘History, origin and extent of soil erosion on Easter Island (Rapa Nui)’, the existence and contribution of soil erosion on Easter’s demise will be examined. Meith and Bork (2005) follow the view shared by Jared Diamond that:

“The isolated Easter Island (Rapa Nui) is an outstanding example of land degradation caused by land use in a sensitive ecosystem”

Meith and Bork (2005) use a detailed analysis of the causes, chronology and spatial pattern of soil erosion on the Poike peninsula on Easter Island to answer the following questions:
   1. Did erosion of Rapa start with the rise of Polynesian agriculture?
   2. Can phases of different chronological differentiation of soil erosion processes?
   3. Was soil erosion a less significant problem in the prehistory of Rapa or was the loss of fertile soils an important reason for the complete change in way of life and culture about AD1400/1500?

Phases of prehistoric land use and soil erosion were investigated in the most eastern part, northwest and southwestern parts of Poike peninsula, whereby all the investigation sites were all characterised by severe erosion. The method for reconstructing past soil erosion is an entire topic in its own right, and a comprehensive methodology is outlined in the paper, however I won’t go into that right now.

Figure 1. Complex of land use and soil erosion in the most eastern part of Poike peninsula near Cabo Cumming

Figure 2. Soil profile from the most eastern part of Poike peninsula

The two figures above represent the soil profile of the Poike peninsula. Historically, the most interesting part of the bottom of the soil profile is the existence of root channels, which have been identified as the Jubaea chilensis palm found on Easter Island when the Polynesians first settled. Above this layer is yellowish soil that shows evidence for planting pits, which indicated agricultural land use. The absence of soil erosion and quality of the soil in both these layers suggests a phase of successful soil protection and sustainable agriculture up until AD 1300. Meith and Bork propose the reasoning for this is because the palm trees protected the soil against intensive radiation, strong winds and heavy rainfall.

The soil profile shows that this phase ended suddenly with the appearance of charcoal in the soil profile. Meith and Bork state that ‘obviously the palm forest was subjected to an extended woodland clearance’, which (in my opinion) is a rather sweeping statement, as if I have shown anything so far in this blog, the controversy surrounding deforestation and the evidence to support deforestation are certainly not clear, and do not merit a statement such as this one.

However, my opinion aside, Meith and Bork continue to suggest that woodland clearance in AD 1400 had dramatic consequences for soil erosion:
   1. Loss of protection from the palm trees caused sheet erosion
   2. Agriculture under open land conditions might have destabilised slope
   3. Erosion and accumulation process shown in soil layer were caused by heavy rainfall and started at downslope areas

This erosion was thought to be the main cause for the abandonment of agriculture in AD 1500, where after AD 1400/1500, human influence can longer be seen in the soil profile.

So what can we infer from soil erosion, and was a contributing factor for the collapse of Easter Island? Well Meith and Bork propose that the sudden shift from the bottom layers to those influenced by humans suggests that the techniques of land use shifted suddenly from traditional sustainable agro-forestry to intensive non-sustainable land use in open land, however the reasons behind this shift are unknown. They suggest that soil erosion and consequently a decrease in soil fertility caused abandonment of agriculture and moai construction on the Poike peninsula, and the burial of settlements. They conclude that:

‘On the basis of results from Poike peninsula, we hypothesis that soil erosion may have had a dominant role in the break down of Easter’s stone culture’

However, soil erosion has only been investigated in detail on the Poike peninsula. We cannot reconstruct whether soil erosion was a contributing factor in Easter’s demise based on one area, thus much more research on soil erosion on Easter Island should be conducted before we can make such conclusions.

That said, it is an interesting thought that soil erosion may have been a contributing factor to Easter Island’s collapse….

A simplified Easter Island story....

So you may be forgiven for getting a little confused over the dates and series of events that happened on Easter Island during its settlement, expansion, collapse and post-collapse….so for your benefit only, I will post this VERY simplified (and potentially controversial due recent research that disputes many of these dates and events) table.

I hope this makes the story a little clearer, as its most definitely going to get more complicated as we bring in more suggested theories for collapse!

Deforestation: A Conclusion

So the intriguing question we can conclude from the last few posts is: Did the Easter Islanders completely destroy the island’s dense subtropical forest, or was Rapa Nui since the beginning of human colonization, a poor environment covered only with local spots of forest, and was it drought and the introduction of rats in combination with humans that finally triggered the extinction of the already rare plant species (Jubaea chilensis).


Due to problems and inaccuracies associated with dating human arrival, deforestation, climate variability and the impact of rats, it is hard to tell which was the dominant cause, or what combination of causes could have triggered and brought about the deforestation of Easter Island. Nonetheless, what we can be sure of, is the deforestation on Easter Island was a complex process. Many scholars researching the collapse of Easter advocate that deforestation played an important, or even central role in the collapse of Rapa Nui, for example Jared Diamond’s highly popularised ‘Ecocide’ theory that humans caused deforestation, which in turn caused their own collapse. However, there are numerous other theories that try to explain the collapse of Rapa Nui, for example overpopulation, soil erosion, warfare and conflict, and the arrival of the Europeans and slave trade. The subsequent posts will investigate these theories as a cause of collapse. 

Easter Island Ecocide: Deforestation due to Humans?

Easter Island underwent deforestation between the arrivals of the Polynesians c. AD 800,and the arrival of the Europeans 1722. The circumstances, causes and triggers of this environmental change have been partly discussed in the last few posts, now this post will attempt to uncover whether humans caused deforestation on Easter Island. This is perhaps the most researched, written about, and debated cause of deforestation, not only because of evidence and support from Jared Diamond’s much publicised view of ‘Ecocide’, but also because of the parable it has for today’s society.

In their paper ‘Humans, climate or introduced rats – which is to blame for the woodland destruction on prehistoric Rapa Nui (Easter Island)?’ Meith and Bork (2010) investigate the causes of deforestation on Easter Island, and concluded that it was humans who caused their own demise…thus it was ‘suicide’.

After settlement on Rapa Nui, population rapidly expanded to a peak of maximum 10,000 (Diamond 2007). The now extinct Jubaea chilensis palm provided numerous uses, including firewood and timber, the construction of canoes, possible transportation methods for the Moai, edible fruits and seeds, and palm leaves that could be used for thatching and rope. As the population expanded, not only did the need for the palm increase, but also more open space was essential for the increased agriculture and number of dwellings and gardens.

One of the best ways to investigate whether anthropogenic deforestation has occurred is to distinguish if charcoal appears in both the pollen diagrams and the soil profile, as this is a clear indicator of man’s influence on the forests. Soil profiles on Rapa Nui provide evidence of ‘slash and burn’ fires in the former palm woodland (as shown by Figure.1), where some of the charcoal layers (specifically on the Poike Peninsula and the southwest of Rapa Nui) contained burned nutshells of the Jubaea chilensis.

Figure 1. Two segments of soil profile in South West Poike. Summarized stratigraphy: (1) Weathered volcanic bedrock. (2) Cone of palm root molds. (3) Pre- clearing garden soil. (4) Accumulation of charcoal from a burned palm stump containing in situ aggregates of burned soil. Result of intentional burning by humans. (5) Charcoal layer. Charcoal layers are best preserved in concave down-slope sections. (6) Post-clearing garden soil with planting pits. (7) Fine layered sediments, resulting from post-clearing sheet erosion of unprotected soil. 

Carbon dating these burnt nutshells indicate that the oldest date of charcoal is around AD 1244-1254, and therefore supports the conclusion made by Meith and Bork (2010) that deforestation and ‘slash and burn’ on Rapa Nui started around the 13^th Century. These findings by Meith and Bork are supported by Hunt and Lipo (2006), where Figure 2 sums of Hunt and Lipo’s work by showing the chronological sequence of slash and burn for 12 sites of Rapa Nui. The suggestion by Meith and Bork (2010) that anthropogenic deforestation started in the 13^th Century is supported by this chronological sequence.

Figure 2. The chronological sequence of slash and burn for 12 sites on Rapa Nui.

From looking at Figure 2, and Figure 3 below, which provides probability distributions for 15 calibrated radiocarbon dates in context with woodland clearance from different sites around Rapa Nui, Meith and Bork (2010) have built up a picture as to what happened on Easter Island.

‘Clearance occurred in phases of deforestation on Poike Peninsula between approximately 1250 and 1510 AD, and at the slopes of Rano Kao roughly between 1400 and 1520 AD. All data demonstrate that the destruction of the palm woodland on Rapa Nui probably lasted no longer that 300-400 years….the main slash and burn activity occurred between 1200 AD and 1600AD.’

Figure 3. Probability distributions for 15 calibrated radiocarbon dates in context with woodland clearance from different locations on Rapa Nui. 

Meith and Bork (2010) thus conclude that:

‘Both the temporal placement (after the onset of human colonization) and the sequential chronology of woodland clearance in different parts of the island underscore that the deforestation was an act of humans’

 This paper also investigate the role that rats play in deforestation (see previous post), and from looking at the nutshells in the soil profile, less than 10% of these charred palm nuts actually contained teeth marks from rats, therefore they conclude that rats are NOT the cause of deforestation on Rapa Nui. They also use a several other lines of evidence to support this conclusion. Firstly, they found that the Jubaea chilensis palm in La Campana National Park, Central Chile, sustains a healthy population of 80,000 palms whilst coexisting with a similar type of rat that is suspected to have inhabited Rapa Nui. And secondly, these rats simply could not have felled mature trees.

Pollen proxies in the lake sediment (Flenley and King 1984) also verify a long existence of the palm woodland (around 35,000 years) on Rapa Nui before the arrival of humans, suggesting that the palms survived all climate variations from the late Pleistocene to the late Holocene.

‘What were the Easter Islanders thinking when they cut down the last tree’?

Once the last tree had gone, they no longer had firewood and timber, ropes, thatching, possible transportation of the Moai, and canoes (their only way off the Island). This then starts the ‘Ecocide’ theory that Jared Diamond suggests….

A quick note: The uses of the palm on Rapa Nui, and the anthropogenic deforestation theory is summed up very well in a paper by Rosalind L. Hunter Anderson (1998). I havn’t used it in my post here as some of the research is slightly out of date, however it does provide a perfect summary of what has been indicated in this post!

Climate Variability, An Afterthought

In relation to my last post on whether climate variability and change could have been a contributing factor to the deforestation of the Jubaea chilensis palm on Easter Island, i thought it was important to share with you a couple of graphs that support this hypothesis.

There is controversy over whether ENSO could have affected deforestation, whereby some studies have found no evident correlation between both variables. However, Stenseth and Voje (2009) show that there is an interesting 'coincidence' between the most intense ENSO (El Nino-Southern Oscillation) activity during the last millennia and the period of deforestation on Easter Island, as shown by the graph below. Could this be more that coincidence? 

It is exceptionally complicated to reconstruct past climatic changes and provide evidence for its relationship to deforestation due to the sheer complexities assocated with the climate system and its relations to bioloy, as shown specifially for Easter Island below.

Again, this reinforces the fact that further research is required on Easter Island before we can be making such claims, which could have significant consequences on the reasons as to why Easter Island was so severely deforested and why its society collapsed.

Easter Island Deforestation: At The Hands of Mother Nature?

As discussed in the previous post, within a matter of a few hundred years, the forested landscape that existed on Easter Island since the Pleistocene disappeared to the grassy stoney landscape that exists today. The collapse of Easter Island is widely percieved as murder or suicide by the settlers themselves…but what if it was murdered by mother nature?

This post aims to assess the theory proposed by Mann et al (2008) in the paper: ‘Drought, vegetation change and human history on Rapa Nui (Isla de Pascua, Easter Island)’, which suggests that climate variability and change caused deforestation on Easter Island.

Mann et al (2008) reports on sediment, charcoal and pollen stratigraphy in the Rano Raraku lake core on Easter Island, and use their results to help identify the timing of widespread forest clearance and help test the hypotheses about involvement of drought. Stratigraphic records from lake sediment cores and slope deposits on Rapa Nui indicate that the Rano Raraku lake basin dried out after 4090-4410 cal yr BP (BC 2140-2460). A depositional hiatus (in this case an angular unconformity whereby younger sediment lies on the eroded surface of older rocks) in the sediment record suggests that drought occurred between 1180-3990 cal yr BP (BC 2040 to AD 770) due to the fact that the soil structure originated from dessication-cracking of the dry lake bed. So what caused these droughts?

There are three meteorological phenomena that are important for controlling rainfall patterns in southeast pacific; Subtropical southeast Pacific high, tracks taken by cyclonic storms carried in the westerlies, and ENSO

1.    Subtropical southeast Pacific High: can block approach of storms carried by westerlies, therefore when it weakens, cyclonic storms track further north (equatorwards) it reduced rainfall and lake levels at Easter.

2.    Cyconlic Storms: Most of the rains come from these cylconic storms moving eastward across the Pacific. Mann et al (2008) argure that shifts in the latitude of storm tracks are probably an important trigger for drought on Rapa Nui, as they shift latitudinally depnding on the overall pole-equator temp gradient.

3.    ENSO: During phases of La Nino, Easter Island experience warmer sea surface temperatures and extended droughts.

Mann et al (2008) conclude that:

“latitudinal shifts in the subtropical storm track and resultant changes in the intensity and frequency of cyclonic storms provide feasible, though untested, climatological trigger for radical changes in moisture balance on Rapa Nui”

They also provide another line evidence based on the knowledge that the geography of the subtropical high pressure system, due to the fact we would expect synchronous droughts on Easter Island and mainland Chile. Based on the Rano Raraku sediment record, the refilling of the lake basin at AD 1180-1290 coincides with the end of a warm and dry climate episode over central Chile, which thus strengthens evidence for drough found in the Rano Raraku sediment record.

There is some literature to support the conclusions made in this paper, for example Stenseth and Voje (2009) present evidence that the ENSO causes reduced marine biomass and resources on Easter, and thus during extended La Nina phases, and other climate variability, reduced marine resources leads to more intensive agriculture on land, or the search for new fishing grounds, both of which require wood of some sort, consequently increasing deforestation.

However, even at a first glance, it is clear to see that many issues surround this theory. Firstly, the trees and shrubs on Easter Island survived climate variability due to ENSO, cyclonic storms and changes in the Subtropical southeast Pacific pressue belt for tens of thousands of years before (Flenley and Bahn 2007), therefore it seems very unlikely that the droughts proposed by Mann et al (2008) could have caused such extensive and widespread deforestation. A paper by Saez et al  (2009) that investigates the sedimentary record of the Rana Raraku lake basin on Easter Island also supports this point, whereby the sedimentary record shows intense drought periods occurred from the mid to late Holocene, yet trees and shrubs survived throughout this period. They also go on to suggest that the Medieval Warm Period aided population expansion, howver because population expansion and deforestation are supposed to go hand in hand, climate is not likely to have had any impact on deforestation.

Secondly, the depositional hiatus in the sediment record is assumed to be caused by drought, however because there is no sediment record, it is impossible to say what the cause of this hiatus is, as we simply have no evidence. As a result, detailed records and evidence of past climate variability on Easter Island remains (and accordingly conclusions as to the effect of climate on Easter’s deforestation) unfeasible to date.

So, did drought and climate variability cause deforestation? From looking at the evidence it is clear that before we can make any solid conclusions on the relationship between climate variability and deforestions, a more accurate sedimentary record is needed. For now though, it is safe to say that it seems likely that climate did not cause deforestation, BUT it could have exacerbated it.

Terry Hunt and Carl Lipo Podcast

Podcast: Terry Hunt and Carl Lipo discuss Easter Island...

Above is a link to listen to a podcast where Terry Hunt and Carl Lipo discuss Easter Island, and their theory that rats caused deforestation with New Scientist's Ivan Semeniuk. Their view on Easter Island, when it was settled and deforestation has caused much controversy recently, particularly with Flenley and Bahn, and Jared Diamond, the most prolific scholars associated with Easter Island.


Enjoy!

Deforestation: The Rat Theory!

The palaeoenvironmental record on Easter Island suggests that the landscape Roggevann arrived on in 1722 would have been very different if he had arrived at the same time as the first polynesian settlers, where the vegetation was once dominated by millions of Jubaea palms. The palaeoenvironmental record indicates that the Jubaea palms have existed on Easter since Pleistocene times, and have survived significant climate changes and numerous environmental perturbations. So what caused deforestation to occur on Easter Island since humans first settled in AD 800-900? The next few posts will investigate the different theories that try to explain this very phenomenon.

Firstly, a theory proposed by Terry Hunt (2007) in his paper, ‘Rethinking Easter Island’s Ecological Catastrophe’ suggests that rats brought over by the first Polynesian settlers were the cause of deforestation on Rapa Nui. In this paper, Hunt advocates that:

“Rats are remarkable fecund and given a nearly unlimited food supply such as the fruits and seeds of pristine native forest, they can irrupt into enormous, dense populations”

By investigating evidence of the relationship between rats and deforestation of palms on Little Barrier Island, New Zealand and Hawaiin Islands, both of these sites underwent extreme deforestation within 200 years due to rat population explosions, and he therefore suggests that recent extinction of palms in New Zealand and Hawaii due to rats can be used as modern analogs to Easter Island’s deforestation. The figure below shows some results from the research on Little Barrier Island, New Zealand, implying a stong correlation between rat population increase and deforestation.

From looking at the closest relatives of the extinct plants on Rapa Nui, the majority were highly vulnerable to impacts by rat predation. Most yielded relatively large edible fruits/seeds, lacked toxicity, and faced destruction rather than dispersal by rodent predation. By using this evidence, and evidence from the abundance of rat bones and skeletons in archaeological  

archaeological excavations and the discovery of many palm fruits with signs of gnawing and removal of the interior nuts, Hunt proposes that rats were the cause of deforestation on Rapa Nui.. He also tentatively suggests that the pollen record shows that the decline of forest pollen (i.e. trees and shrubs) started to decline BEFORE charcoal and charred remains were found in the pollen record (indicators of burning caused by humans), however the pollen-charcoal evidence from Rapa Nui must be understood more fully before he can make such conclusions.

However, Hunt’s theory that rats caused deforestation on Rapa Nui has been contradicted by numerous lines of evidence proposed by Diamond (2007), Flenley and Bahn (2007), Meith and Bork (2010) and Rolett (2008).

1.   Rats simply could not have felled the mature trees, which grew from between 15 and 30m high. The life span of some of the trees reached 2000 years old (Rolett 2008), and from looking at pollen evidence undertaken by Flenley and Bahn (2007), deforestation occurred quite rapidly (on some parts of the island within centuries of the first settlers arrival), and therefore rats could not have caused deforestation on such massive trees within this short time period.

2.   Research undertaken by Meith and Bork (2010) drew attention to the fact that healthy populations of a similar type of palm to the once grew on Easter Island, Jubaea Chiliensis, coexists with rats on mainland Chile.

3.   Among more than 200 completely preserve and charred nutshells that we discovered in the burned layer of a pollen record undertaken by Fleley and Bahn (2007), whereby  less than 10% of the nutshells had bite marks. Thus indicating that the extensive deforestation attributed to rats by Hunt may not have been extensive as he insinuates.

4.   There is a wealth of evidence to suggest causes other than rats were the major cause of deforestation (to be discussed in following posts), for example climatic variability and drought, and human impacts.

Despite the contradictions and controversy stemming from the theory that rats caused deforestation on Easter Island, both the proponents and opponents agree on Hunt’s concluding remarks in his paper that firstly,

“Additional research will be essential to disentangle the contributing factors…the environmental catastrophe of Rapa Nui is likely a complex history”

And secondly,

“As biological invasions and extinctions continue at unprecedented rates, deciphering ecological histories and the consequences of biological invasions has gained urgent significance.”

References

Flenley, J. and Bahn, P.G. (2007) The Enigmas of Easter Island: An Island on the Edge Oxford: Oxford University Press