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!