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.