Concluding thoughts Part 1 - The Forests

Firstly I'd like to say sorry for a long gap between this and my last post but you know what it's like going back to the family home at Christmas! Anyway, back to Easter Island! In this and my next post I will be concluding my thoughts about the mysteries of Easter Island; what caused the forests to deteriorate and what caused the population to collapse? In this post I will be looking at the forests. The conventional story argues that the islanders put too much pressure on the forest, both for food resources and for wood for canoes and the statue building. Other writers argue the importance of climate change while others put further alternatives to blame, such as rats and so on.

Rollet and Diamond (2004) argue that the key issue facing the island was that the geography of Easter was extremely vulnerable, to an extent that it was predisposed to deforestation. Receiving some of the lowest amounts of volcanic dust and tephra than any other Pacific islands meant poor soil quality and receiving a relatively small amount of rainfall but reasonably strong winds compounded this. The island was therefore very fragile, and the presence of some thousands of Polynesians that were dependent on the land for most resources would have put enormous pressure on the environment.

Hunt & Lipo’s (2009) paper observed that the greatest period of deforestation (around 1200AD) occurs several hundred years before the only sustained population decline on the island that occurs after European contact, suggesting that the islanders were not the sole driver of deforestation as they were not solely dependent on the forest for all their resources. As Hunt & Lipo (2009) add, the islanders developed numerous adaptations to the poor geography of the island to cope with resources scarcity, suggesting that they did not just thoughtlessly put up with an increasingly degraded environment. Furthermore, as I discovered in this post, the islanders may not have even used trees that heavily for statue building and transportation, which is a key source of blame in the conventional argument. 

This conclusion therefore led me to look at the role climate could have played in deforestation. One of the first things I noted while researching this was Hunt’s (2007) observation that Easter’s forests survived thousands of years of climatic changes since the Pleistocene, suggesting that it is unlikely climate could be solely to blame. Junk and Claussen (2011) developed climatic models to observe the influences El Nino Southern Oscillation could have had on Easter’s vegetation, as well as the impact of volcanic eruptions, the Medieval warming period, the ‘Little Ice Age’ and a number of other climatic variations. They concluded that no significant or even marginal changes in vegetation or forest cover was observed as a result of climatic variations between 800 and 1750AD on Easter. Although they add that is possible small scale changes in climate could have been important, such as localised droughts, a crucial issue is that there is no direct information about climate change on Easter (Mann et  al.2008).

Since it seemed that it wasn’t just the islanders that pushed the environment to the limit, and that climate was also not to blame, I looked for alternative explanations. One argument is that rat populations on the island would have been able to grow on the island without predation (small island with low biodiversity and lack of predators (Diamond 2005)), putting enormous pressure on forests as they are able to prevent them regenerating through their use of tree nuts as a primary food source (Hunt 2007). Hunt (2007) noted that as the forest declined, so did rat populations, making this an interesting argument. Andreas and Bork (2010) noted several issues with this argument, an important one being widespread evidence of felled and burnt trees across the island, suggesting that both rats and humans played relative roles of important. I therefore conclude that it is likely the combination of human and rat pressures on the forests in an already fragile environment was the main cause for deforestation, with localized droughts probably also playing a role.