Saturday, November 14, 2009

Rats! (and German Ecologists)

Today's USA Today covers a new paper that is just being published in the Journal of Archaeological Science by ecologists Andreas Mieth and Hans-Rudolph Bork from the Institute for Ecosystem Research in Kiel, Germany. This paper "Humans, climate or introduced rats – which is to blame for the woodland destruction on prehistoric Rapa Nui (Easter Island)?" challenges Terry Hunt and my argument that (1) Easter Island was colonized in AD 1200 and (2) that rats played a role in transforming the ecology of the island.

Their argument sets up our previous work as a "straw man." They claim that we argued that rats *only* caused these trees to go extinct. This is, of course, absurd - trees were primarily destroyed by burning, not rats. Rats, however, must have had some impact on the environment simply because (1) they were there, having been introduced when people arrived (2) rat populations must have been large, based on the lack of natural predators and the plethora of food provided by the Jubaea chilensis palm (i.e., nuts). All we are saying is that this aspect needs to be considered when putting together the overall explanation.  

The real point of contention is what prevented regeneration of the forest, not what cut it down. The fact that there was no forest regeneration is fairly clear from archaeological evidence (made by a variety of folks). While we see prehistoric sedimentation, we don't see palm root molds other than those made in the pre-human occupation surfaces. Mieth and Bork, following the standard "catastrophe" story believe that the lack of regeneration is due to erosion and ecological collapse. I would argue that rats would have made it difficult, if not impossible for the trees to regrow - and that humans would have had little incentive to regrow these slow growing trees (Jubea palm live up to 500 years) especially since any new trees would harbor more rats. Much of the differences in these stances has to do with what one assumes the productivity of the wooded environment was like -- they assume that the productivity was high (because it was forested). I think the evidence speaks otherwise.

I've been working hard on this part of the story for the book - it forms the focus of a chapter we call "Resilience." Where this covers the conditions that prehistoric populations faced when they arrived on the island, the materials/technology/plants/animals they had with them, and the details of the history resulting from this combination. It's coming together...

Below is what I do not think is the case. It just didn't happen. More on this later...

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