Sunday, November 17, 2013

Response to Comment

 

A Sophist wrote a comment in response to the blog entry Diamond attempts to defend myths of Easter Island: Lipo and Hunt respond :

My questions remain: 1. Were there Palm trees on Easter Island when the first Europeans visited? And if not, then H+L are arguing this was rats and not humans cutting the trees down? 2. If Palm Trees are unable to be made into canoes, how did the people make ocean going canoes? In there were no canoes, how did Dolphin get into the diet? I guess I am missing the problem. This seems to be a lesson in how isolated political leaders who do not feel the pain of their actions (cutting down the forest for whatever bloody reason: fuel, canoes, to move statues, etc) can lead their society to the brink of destruction. 

The questions themselves point to common but false assumptions often made about Easter Island prehistory and they are worthing examining. 

Question #1:  Palm Trees.  I’m not sure how the two different parts to the question are related (i.e., whether there were palm trees at contact in 1722 and whether rats “cut down” the trees). For the first question: no one knows exactly whether there living examples of palm trees on the island in AD 1722 when Roggeveen first arrived nor later in the 1770s when the Spanish and English arrived.  The overall impression we get from these early written accounts is that the island was largely devoid of trees though there are also mentions of “palms” in some of the descriptions.  The pollen and macro  botanical record is equally unclear given the relatively poor dating of the island as a whole and relatively few dates of palm nuts in particular. A major effort to date events on the island (with modern understanding of the need to link past events with dated events) would go a long way to resolve this issue (among many others). 

One difficulty in resolving pre- versus post- contact differences in the island’s landscape and ecology is the fact that point at which researchers arrived on the island to make systematic descriptions is more than 250 years after initial contact and decades after the island was turned into a sheep ranch. Certainly, the presence of 60,000 sheep and associated ranching activities likely resulted in the final termination of many plants that may have been present in small numbers in late prehistory.  So the timing of the final termination of the palm is still a bit unclear.

The second part of the question seems to assume that we (Hunt and Lipo) argued that it was “rats… cutting the trees down.” The statement is absurd to begin with and of course we have never argued this. What we have argued is that arrival of rats with humans on to the island brought immediate and substantial changes to the ecology of the island. The introduction of rats is really the introduction of the first teeth on the island and their presence (as is well documented in many environments) will impact native vegetation especially that which has coevolved dispersal mechanisms with birds. The impact of rat is a fact and indisputable given the evidence that exists of rat gnawing seeds. But did they “cause” the trees to go extinct (as this question implies we say)?

The answer is, of course, no. The rats did not cause the palm forest to go extinct for several reasons. First, things don’t “cause” other things to happen except in common sense (see Sellars 1963: Science, perception and reality).  Second, while rat predation on palm nuts has been an ignored factor in the vegetation changes that are commensurate with human arrivals, rats were not the sole factor.  We *do* know that rat predation on seeds can make massive changes in vegetation and even extinction even when humans are not present.  As Hunt has discussed, the elimination of Pritchardia palm in the Ewa Plain clearly predates the actual arrival of humans (see Hunt, T., 2007. Journal of Archaeological Science 34 (2007) 485-502; Athens, J.S., Tuggle, H.D., Ward, J.V., Welch, D.J., 2002. Avifaunal extinc- tions, vegetation change, and Polynesian impacts in prehistoric Hawai’i. Archaeology in Oceania 37, 57-78.p. 73).

On Easter Island with its tiny size (about 6x10miles), however, there was never a point at which rats were separate from humans. It takes about an afternoon to walk from one side of Rapa Nui to the other: human and rat impacts will be effectively simultaneous across the the entire island.  We know that the people arriving on Easter Island were slash-and-burn cultivationists — a strategy we side widespread across the Pacific (and indeed around the world). Their lives depended on transforming the environment to one that was capable of supporting human life through the growth of Polyensian domesticated plants. Thus, humans burned the forest down right from the get-go.  The combination of human burning for land clearance with rat predation on palm nuts would mean that the forest have a difficult time to grow back on its own.  Recent excavations by a Belgian team up at Vaitea (I believe: I heard about this second hand) show that in prehistory there were attempts to grow these palm trees. This is not at all surprising: the trees were certainly disappearing given activities of slash-and-burn and rat predation and this would be something that prehistoric people noticed (contra the assumptions inherent in claims by Diamond). 

What gets confused as a claim that we (Hunt and Lipo) argued that rats “caused” palm tree extinction are some comments that Hunt made in his paper in American Scientist that:

 

The evidence from elsewhere in the Pacific makes it hard to believe that rats would not have caused rapid and widespread environmental degradation. But there is still the question of how much of an effect rats had relative to the changes caused by humans, who cut down trees for a number of uses and practiced slash-and-burn agriculture. I believe that there is substantial evidence that it was rats, more so than humans, that led to deforestation.

and in his 2007 JAS article where he says:

 

In this review I have examined ar- chaeological, palaeo-environmental, and contemporary eco- logical evidence to suggest that the Pacific rat may have played a major role in Rapa Nui’s ecological catastrophe. The fact that rats alone are capable of widespread forest de- struction compels us to evaluate their contribution to the trans- formation of Rapa Nui, as well as in other island ecosystems. While I argue that the role of rats has often been underesti- mated, direct human actions of felling and use of fire likely have played a significant role as well. Additional research will be essential to disentangle the contributing factors. The environmental catastrophe of Rapa Nui is likely a complex history, one that has been masked by speculations about the in- tentions of people cutting down the last tree. Indeed, the ‘‘last tree’’ may simply have died. Rats may have simply eaten the last seeds. Perhaps the lessons of Rapa Nui tell of the effects of invasive species, invasional meltdowns, and the synergy of ef- fects that ensue as people and their portmanteau biota reach evolutionary isolates in the remote islands of the Pacific. 

But what is clear in the context of these quotes is that what Hunt is arguing (as we both do later on) is that the loss of the forest is the outcome of a number of factors among which rats is one. It is certainly possible to argue that rats could have caused the extinction of the palm trees, but in the case of Rapa Nui it also seems clears that the rat predation was occurring simultaneously with human burning and clearing of the palm forest. Empirically, this is undebatable  as we have rat gnawed seeds that are found contemporaneously with burned palm. 

It is also silly to argue that the presence of non-gnawed seeds somehow “disproves” the role of rat predation. Some nuts probably didn’t get eaten especially if the tree was burned before the rats were able to consume them.  Even a small impact to seed production for these trees is likely to have caused changes in the life history structure of the forest whereby there become fewer and fewer young trees. Rats do not have to eat every single palm nut for the forest to go into major decline or even extinction. Clearly the r-selected strategy of palm trees embodied by nut production is a testament to the fact that the palm is evolutionarily successful by maximizing the number of offspring due to the fact on average some of the nuts will grow into new trees, not all.  The novel introduction of toothed predators likely only had to have a small effect to have upset the balance between forest regeneration and failure. Of course, this is topic that clearly needs more research. 

Question #2:  Canoes and Dolphins: In the second part of his/her question, A Sophist writes: "2. If Palm Trees are unable to be made into canoes, how did the people make ocean going canoes?”  I guess the assumption here is that the presence of dolphin remains at Anakena must somehow have required large ocean going canoes. It also refers to the fact that we argue that palm trees are not useful for constructing canoes, at least not the sailing/voyaging canoes used by Polynesians. To disentangle this question, let’s start by saying that it is likely that whatever canoes brought people to Easter Island were likely around for some period after their arrival. We don’t know this specifically since we have no evidence but the faunal record seems to record more deep water/pelagic fish in the early assemblages than later. The acquisition of these fish would have required canoes and early on there would have been the original canoes to use.  It also seems that at some point these canoes rot away, are lost, or used to sail elsewhere as the faunal remains show significantly less pelagic fish. From that point on the emphasis of the population was nearly entirely on terrestrial resources (though some small % of fish from the limited nearshore reef seemed to supplement the diet). The palm trees appear to have been lost over 4 centuries were not used in canoe manufacturing even though they were present.  This is almost certainly because palm trees are not good raw material for canoes: they are flexible grasses filled with mush. 

The presence of dolphin remains at Anakena is certainly interesting but it doesnt seems to contradict our overall understanding of the archaeological record.  The remains are few in number and were never a major source of food. Ethnographically we know that dolphin come into the Anakena bay and were sometime hunted there. The bay is shallow. Traditional means of hunting dolphin often involved trapping them in shallow water by driving them toward shore with rocks knocked underwater (see http://www.youtube.com/watch?v=QP3FbrF5YyM if you stomach it). Deep water canoes were not necessary for hunting dolphin. 

Final Comment:  The final comment by A Sophist is a bit puzzling: "This seems to be a lesson in how isolated political leaders who do not feel the pain of their actions (cutting down the forest for whatever bloody reason: fuel, canoes, to move statues, etc) can lead their society to the brink of destruction. “ It is not clear at all what “this” refers to or who the “isolated political leaders” are or what “brink of destruction” means. Inherent in here is the idea that somehow the forest was a vital resource upon which people depended. The fact is that there is no evidence that palm trees ever played a central role in the subsistence or settlement activity of people of the island. As sweet potato farmers, the clearance of trees (like all farmers) resulted in more land available for growing crops. The burning of the forest resulted in temporarily increased nutrients in the soil. The fact that rat predation (not to mention the slow growth and reproduction of the tree itself) meant that the forest never regrew was not a catastrophe. Alternative (laborious yet, but indeed clever) means of enriching the soil through rock mulch as well as intensely tended gardens (manavai) were able to keep the soils growing food. The trees simply were not a vital resource to the prehistoric population.

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