This week we'll be reading:
Li, Jinbao, Edward R. Cook, Rosanne D'Arrigo, Fahu Chen, Xiaohua Gou, Jianfeng Peng, and Jianguo Huang. 2008. Common tree growth anomalies over the northeastern Tibetan Plateau during the last six centuries: implications for regional moisture change. Global Change Biology 14: 2096-2107.
This week, when you are reading the paper about tree rings and climate in Tibet, be thinking about how those methods could apply to other studies. Last week, we had a good discussion regarding the collapse of Copan. If you were to conduct a study using tree rings and similar metrics to those used in the Tibet study, how would you apply those to Copan to answer hypotheses? What other metrics would be useful? Be specific about your hypotheses and sample sizes and describe what your hypothetical dataset would look like. What other forms of data would be useful to determine the Copan collapse? Think of at least three. Be prepared to discuss your hypothetical experiment and blog post and have the class scrutinize them like we did for the palynology paper last week!
My tentative hypothesis is that between 400 A.D. and 900 A.D. there were several natural and human factors leading to two deforestation events in Copan, Honduras. The natural factor were episodes of decreased precipitation in the Copan region, coupled with deforestation due to fire, which resulted in erosion as evidenced by the pollen-inferred changes in vegetation in the sediments in lower watershed reservoirs . Tree ring records are a source of information for determining drought conditions on a regional scale. Tree ring anomalies are linked to availability or lack of available moisture. Pollen taxa is high when there is regional land clearance. As vegetation may be influenced by climate changes carbon isotopes are obtained to determine any change from C3 to C4 flora. Erosion rates may not be adequately explained by the drying of vegetation alone. There appears to be an unknown factor operating in this region as the human population in this area was low when the erosion rate was the highest and the population peaked when erosion diminished.
ReplyDeleteThe study of tree rings is very useful in seeing climate change, but trying to show a collapse of a civilization must go beyond climate data. There is no way to say that a civilization perished based on the climate evidence found no matter what evidence there is. We have to look at archaeological records, dig sites, or, if we are lucky be able to decipher the language of the civilization. So, I don’t really know what you guys are wanting in terms of data when the data you want us to use could only be secondary to the actual physical evidence at hand.
ReplyDeleteIf you wish to see if the civilization was dealing with harsh weather conditions then tree ring data is a great start. I will look at both the tree rings from the building structures, if any and the rings from the terrain. Also the different isotopic analyses can help show that there either was or not harsh living conditions. Next I would look for evidence of their crops. In doing this I can see what kind of crops are in abundance or those that are scarce and figure out which kind of climate is needed for the success or failure of said crops. If I were to go with the pollen, which we all know can be dodgy, and then I would take the deepest core I could from several locations and try to make the best statistical model for the job. I will look to the trees for damages, and in doing so try to pinpoint in the historic record what kind of incident happened around the time of the scars and see if I can closer pinpoint the exact dates of some of the data sets. I would also interview people from close civilizations to see if there was a movement rather than a destruction of the people in Copan, much like the Mayans. If, at my disposal are any animal remains of the time in question I will look to their teeth for isotopes and micro-wear patterns to again try to distinguish vegetation and the climate needed for the said vegetation.
After doing all of this I would qualitatively match the finding with the other data sets and the climate records to see if there was indeed a climate hardship. However, my real evidence of causation would be from the archaeology and form their decedent’s culture, if there is any. I guess my Hypothesis would be that, if climate was a factor, the people would not be able to grow their crops and had to move.
I would gather tree samples from areas all around and close by Copan to see what kind of info could be used with the pollen data. I would also want to see if I could find remains of animals to look for information there as well. I would want to see if the tree ring data gave any info or clues like a prolonged drought that may have drove the civilization out. My hypothesis would be what can tree ring data if any tell us about the Mayan civilization at the end of their presence.
ReplyDeleteThe hypothesis for the Copan paper is wrapped around the failure of the Mayan civilization at a particular city. Pollen evidence from grasses and maize are used to argue the loss of forest,. Therefore tree ring data would be a good construct for making their argument more thorough. Trees currently in the area that date back to the early to middle period may be difficult to find, they would almost need to be similar to our bristlecone, but if found they could show climatic conditions.
ReplyDeleteTree core data could be used to develop an historical picture of the climate in Honduras over time from which to construct a likely scenario of how the trees would have grown during the classic to pre classic ages. Pine pollen was found in the post classic period up to 1500 which indicated to the authors that fewer people lived In the area and dendrochronology possibly corroborate this claim.
It is pretty clear that neither pollen nor tree ring data are enough to make strong claims about the growth patterns, climate or sociological behavior of the Maya.
Tree ring data would counter-balance evidence indicating over deforestation. If trees grew very slowly a drought may be indicated.
Since Honduras is in the Northern Hemisphere it likely experienced the drought that Tibet experienced during the same period, between 1400 and 1600 AD. That data can be used to develop the argument that climatic conditions had a considerable effect on the population/culture of the Maya at that time. According to the Tibet paper, the most effective monsoon for growth was the early and was linked to the tropical Pacific ENSO, which also strong controls the climate of Central America. So climate data could round out the pollen and tree ring data. Maps such as the correlated precipitation maps could be used to construct a model of the environmental challenges they faced. The lack of diversity is the greatest failure of the Copan paper, the more possible cohorts brought in to the data bank the greater will be the understanding of the people and their civilization.
Tree ring data seems to be the best bet in reconstructing climate and should have been used in Copan. In the Tibet paper I definitely liked that they had more than a single tiny sample. In Copan I would take tree ring samples from the surrounding lake, animal or human remains, and perhaps any historical accounts or even agriculture counts from the population itself, with drought would come a decrease in crops.
ReplyDeleteI feel like tree ring data would only be useful for the Copan paper's hypothesis if the cause for the city's collapse was a climate change. Tree rings don't really address deforestation, unless you could gauge the age of many trees in the area (if many of them dated back to before the collapse, then they were around during the collapse). ... New data could be collected maybe, if trees grew in a different way when recovering from deforestation.
ReplyDeleteTree rings might show if there was a prolonged drought, though this paper seemed to say that the amount of precipitation mattered less then when that precipitation was falling, therefore it is possible that changes in precipitation that affect crops would not affect trees or vice versa.
I feel like tree ring data may have helped the argument in the Copan paper in showing whether some type of drought existed. From this the authors could have looked into other factors like lack of production in agriculture as an explanation for the collapse. As we have heard in class agriculture is the factor that determines population expansion. So as far as I’m concerned it would have to be something major like this that would lead to a collapse or lead to a breakdown of their society. As far as I know the Mayan depended on rainfall for agriculture so the tree ring data could help to either shore up that idea or disapprove it. However, would there be trees available to get tree ring data being that the argument was that deforestation led to the collapse? Overall, I would argue that everything from tree ring data to archaeological evidence would have to be taken into account to explain the collapse.
ReplyDeletePost 1 of 2. Climate and environmental change can be used to detect changes and periods of extreme stress (such as periods of fire) but I have to agree with Zach that trying to show a collapse of a civilization must go beyond climate data and show substantial evidence of broad scale societal collapse. The Copan paper (McNeil et al. 2009) found that evidence of civilization destruction was low during these periods and that the deforestation was caused by agricultural development. It would be possible to use the dendric record to show whether there were periods of drought associated with collapse of civilizations by examining the archaeological evidence for collapse conditions or changes in habitation zones. It could also show if there was a catastrophic event like a fire or extreme drought. The data from such evidence is strong if it is used in conjunction with actual signs of collapse. I am particularly interested in collapses in Europe and the Middle East, but tree data is not really available for those areas. I think it is sort of strange that people pin so much on dendritic effects in Mesoamerica because the trees are primarily showing a pattern of monsoons with a gradual warming over time. This is not beyond the ability of civilizations to cope with; people must have adaptive strategies which are at least moderately able to cope with drastic changes in immediate climate, because otherwise we would be extinct. As a species we have a lot of adaptations to cope with temperature and environmental change and as a social species with cultural modifications to local environments and other buffer mechanisms we are extremely good at adapting to environmental change.
ReplyDeletePost 2 of 2.
ReplyDeleteIsotopic analyses of skeletal remains in the area (both human and nonhuman) would give a clearer idea of what the civilizations of the past may have faced when dealing with environmental change. The paper on the tree rings and climate in Tibet was interesting. It seems like these methods would work well in other environments with extremes in temperature like Tibet has. For example, tree rings in Finland may be more informative of extremes in climate change while tropical tree rings would reflect long term and short term changes in monsoon patterns. The monsoon pattern data could be used in conjunction with fire records to determine weather and fire relationships and this could be used to see what changes in human societies. The methods could easily be applied to many other kinds of studies depending on what data you wanted to determine and what type of climate and seasonal patterns existed at different time periods in recent earth history. The collapse of Copan could be studied using tree rings and similar metrics to those used in the Tibet study, by applying those to Copan to answer hypotheses regarding drought hypotheses which exist in relation to the collapse of Mesoamerican culture groups, by showing if the trees experienced a period of very high stress and maybe also fairly large fires. Palynological data like that used at Copan would be useful, isotopic data from land animals would also be useful for testing that hypothesis. I don’t understand what is meant by “be specific about your hypotheses and sample sizes and describe what your hypothetical dataset would look like” I guess it would probably match up pretty well and that it might also match isotopic records from deep sea cores. I would like more than 20 and less than 500 data points in a single study so that individual variation would not skew the results. I think palynology, Lake Core isotopes, Gulf of Mexico sea core isotopic data, and land mammal data would present a clearer picture of the Copan collapse. The most likely current hypothesis in the Archaeological world is that Copan lost trade contact (probably because of a disease outbreak) and that within about 50 years the city’s glory period was over and the population had plummeted. We are culturally buffered and supported from long supply chains. I guess my specific hypothesis would be that the Copan collapse was caused by something other than a climate episode because there does not seem to be any correlation between the time of the collapse and a climate event in the record (at least not beyond ranges found in the current climate period) therefore there is less likely to be a climate event than some other cause.