This week we're learning about using pollen records to learn about paleoclimate. We'll be reading:
McNeil, Cameron L., David A. Burney, and Lida Pigott Burney. 2010. Evidence disputing deforestation as the cause for collapse of the ancient Maya polity of Copan, Honduras. PNAS 107:3, 1017-1022.
(Note that on the wiki, the paper is listed as McNeil et al 2009 - this is a typo.)
As you read this paper, think about how the data are analyzed and interpreted. What, if anything, would you have done differently with the pollen data?
Mike J
ReplyDeleteThe first thing I would have done differently is collect multiple samples. Understanding the time involved in analyzing each sample; the arguments and new suggestions/disproving deforestation as the main cause of the downfall of ancient Maya inhabiting Copan, Honduras would have been much stronger.
I would also have found a way to include the best known climactic data from the region during the incorporated times, as a way to discard possible pollen gain or loss from environmental factors.
When reading the article I was wondering about wind directions and speeds and how that might affect the pollen dispersal.
Were there any other pond/lakes in the region to have yet further samples to strengthen the argument?
The argument that deforestation was the main cause of the decline/loss of humans in the region, to me seems very week. If my plan was to write a paper to some what disprove this hypothesis; there seems to be many other assumptions and/or holes in the hypothesis that could have more strongly emphasized.
One thing that comes to mind is, how much pollen actually gets deposited in a (guessing) small pond from an intact unfragmented forest. It would seem that in the Mayan would have prcticed a more sustainable forestry practice such as, harvesting small patches; this would cause a larger surface area of forest to unforested land and would allow more pollen to be dispersed by wind unabaided from high density of trees and accumulate at higher rates in the pond. If this suggesting even makes sense, it would show up as less forestry in the pollen analysis.
The paper by McNeil, Cameron L., David A. Burney, and Lida Pigott Burney. 2010. Showed evidence disputing deforestation as the cause for collapse of the ancient Maya polity of Copan, Honduras and was published in PNAS.While I was reading it, I felt that the data are not very easy to interpret and that sub-sampling may cause a lot of pollen to go uncounted (especially if there are not many pollens of one species in the sample). I think I would have gotten more samples and perhaps taken more than 1 sub-sample from each sample core. I can see why statistics is a difficult way to interpret this data and that any differences in pollen counts could skew the results by many percentages.
ReplyDeleteWell I am glad I am not the only one that has some issues with this paper. Al-in-all I agree with both Mike and Jayda, there seems to be good hypotheses without the data or explainations to really, in my opinion, justify all of their explainations.
ReplyDeleteI must admit that I am nervous about conclusions made by examining relative pollen abundance in 1/2 cm^3 samples of the core. That sounds like a tiny amount to me! If sediment deposition (inc pollen) changes slightly across locations of the pond, wouldn't this alter the composition of the core and thus be very different from cores taken from slightly different locations? Larger sample sizes or perhaps sample pooling would seem to be the solution.
ReplyDeleteAlso, it would seem that a pond or any other water source may have provided utility for early inhabitants. If this pond or its nearby inputs were ever used for washing, irrigation, drinking water, etc, wouldn't these activities influence pollen? If, as other cultures have done, felled trees were floated in a watercourse for transport or something, this could change the pollen record drastically.
The paper was confusing. It seems like there should be more items looked at. There seems to be too many variables with the pollen. I agree that the climate should have been looked at more closely. I agree that with the conclusion of the paper that deforestation did not cause the collapse.
ReplyDeleteOverall, I thought the deforestation hypothesis just wasn’t a solid argument proposed by the authors for the collapse of the Mayan people. I can somewhat understand their hypothesis in that when you slash and burn an area over time it loses its nutrients. Therefore, this would lead to a lower production in the crops grown within the region to support a large population. Yet, the authors seem to take the approach that it is because of physical erosion of the sediment that leads to the collapse. I guess this is where I get confused because I believe that there are many more reasons for the collapse then just deforestation. I would argue something more drastic had to have happened because I feel like their argument was based on a gradual process that over time a population like the Mayan people would have accounted for. I feel like as a population expands it has the ability to expand it boundaries until it has nowhere to go and as far as I know there are not any major boundaries that restrict the Mayans besides maybe something politically or socially. With that being said if there wasn’t something holding them back from expansion they would have been able to further develop other agricultural lands to account for at least sustaining a population. But overall I thought the paper was pretty cool in that it incorporated geology (sediment cores), biology (pollen), and anthropology (Mayan collapse). I think that this paper showed how all fields of study must be incorporated to get a better understanding of the past.
ReplyDeleteI agree that more samples should have been taken it seems like a far leap to make conclusions from that. Im sure that deforestation would cause problems for a population but it cannot be the only cause.
ReplyDeleteTo take this paper seriously I would first want to know how much variation is possible in multiple cores from different areas of the same pond. It seems too likely that a change in the morphology of a pond or the area around it would modify the deposition of pollen at its base. There wouldn't be a uniform layer of pollen across the bottom of a pond.
ReplyDeleteAnother problem is that deforestation is NOT an adequate reason for an entire population to just disappear unless the deforestation was virtually complete. In other areas of the world slash and burn agriculture was practiced for hundreds and sometimes thousands of years without completely depleting local forest resources, it seems unlikely that this population would fail due to deforestation.
I would like to see archaeological records from this area to determine what else could be the cause. I would need to look at any available skeletal remains, changes in architecture, shifts in location or increased contact with other cultures, especially changes to weapon quantity or quality.
There are too many potential reasons for a population to fail for me to give complete credit to an idea based off of one pond core sample of pollen.
Metta RavenHeart. The authors have a viable point in arguing that deforestation cannot be proven to be the cause of collapse of the Mayan culture. Their use of pollen data add to their argument but it is far from enough to convince one of what the environment was truly like.
ReplyDeleteIt is possible that the Maya were practicing fallow time agriculture and allowing the forest to regenerate while moving their intensive agriculture to other areas, perhaps even for considerable lengths of time. They were also possibly using wetland species in their agriculture. For this reason I think the wetland pollens should probably used with forest and herb pollen ratios, it is fair to include all of those data to create a more accurate picture of their environment.
Drought is definitely a possibility, along with other climatic conditions and those data need to be included in the data analysis and not just discussed as possibilities. Large forest fires and successive grassland and reforestation processes could be an aspect of climate.
Along with that is the need to study the lives and agricultural practices of the Maya descendants today as they are very successful, sustainable farmers and are undoubtedly practicing knowledge passed down from their ancestors. It is important to remember that these civilizations did not disappear, they ebbed and flowed and moved on.