Week 9: Abundance and Distributions (continued)
Paper for Thursday: Changing Patterns in the Holocene Pollen Record of Northeastern North America: A Mapped Summary (1977)
Commentary author: John W. "Jack" Williams
Jack Williams is currently the Bryson Professor of Climate, People, and Environment in the Department of Geography at the University of Wisconsin-Madison, as well as the director for the Center for Climatic Research. He was also a research associate at the Limnological Research Center at the University of Minnesota from 2003-2004. Williams' research interests nicely tie in with the subject of today's paper: he mostly looks at Quaternary paleoecology, atmosphere and vegetation dynamics. His lab's main focus is on vegetation change and its link to environmental fluctuations.
Paper authors: J. C. Bernabo and T. Webb III
Thompson Webb III received his PhD from the University of Wisconsin-Madison in Meteorology in 1971, where he studied fossil pollen for evidence of climatic sequences. Webb was at the forefront Quaternary paleoclimatic studies when it was still becoming a hot topic -- his major contribution was pushing the use of paleovegetation data (and not just paleoceanographic data) in paleoclimatic simulations like CLIMAP, as well as helping lead the project COHMAP, and contributing to many databases. After 2 years of postdoc, Webb started work at Brown University and never left. He is now an emeritus at Brown.
J. Christopher Bernabo was one of Webb's first graduate students upon Webb's arrival at Brown. Bernabo obtained his PhD under Webb in 1977, and worked with him on a postdoc for 3 years. I could only find two scientific papers authored by Bernabo - this one and another from 1981 - but I did find that he was the second AGU Congressional Science Fellow, and worked in the office of a Californian representative from 1978-1979. It looks like he got really involved in pushing the issue of modern climate change on politicians and decision-makers.
Cliffnotes:
This paper came out during a time when Quaternary paleoecology and climatic reconstruction was growing in popularity. The CLIMAP (Climate Mapping and Prediction) Project (on which Tom Webb collaborated) published the first reconstruction of the LGM around this time. Reconstructions like this required all sorts of information including ice sheets, micropaleontological data, and vegetation patterns.
In this paper, Bernabo and Webb provide the first paleoclimatic reconstruction with pollen data in the northeastern United States, where effects of climate change can be well-traced throughout the Holocene. The pollen studied are from spruce, pine, oak, herbs, and the BAFT group (representing the boreal forest, conifer-hardwood forest, deciduous forest, the prairie, and northern hardwoods, respectively). By mapping pollen occurrences through time, Webb and Bernabo get a broad sense of vegetation dynamics and responses to climate change in the area.
Vegetation patterns were mapped from 11, 000 BP to present, each over 1000 years. Pollen was collected from 62 cores, both published and unpublished data, from around the northeastern United States. Isopoll, difference, and isochrone maps were constructed for comparison of vegetation ranges through time. Vegetation patterns were mapped along with paleogeographic features like ice sheets, glacial lakes, and shorelines so that a more well-rounded overall picture of paleoenvironment could be seen at each time.
The results show the shrinking and redevelopment of a boreal forest; expansion of pine followed by the replacement by oak; the changing composition of deciduous and conifer-hardwood forests, along with the expansion of the BAFT group within the latter; the westward retreat of prairie and forest following 7000 BP; and increase in herbs following the immigration of Europeans. These pollen changes or migrations can be related to changes in glacial conditions; a decrease in pollen variability (i.e., an increase in vegetation stability) occurs around 7000 BP, correlating with the disappearance of the Laurentide ice sheet.
This paper likely helped Webb and his colleagues develop COHMAP (Cooperative Holocene Mapping Project), an interdisciplinary project similar to CLIMAP that looked not only at the LGM, but also at the interglacial conditions that followed. The authors provide a few reasons for the movement of vegetation (glaciation and deglaciation, immigration of new taxa, further development of already-present taxa) - maybe think about what other factors could be affecting the patterns seen here? Could there be anything biasing the data?
Cliffnotes:
This paper came out during a time when Quaternary paleoecology and climatic reconstruction was growing in popularity. The CLIMAP (Climate Mapping and Prediction) Project (on which Tom Webb collaborated) published the first reconstruction of the LGM around this time. Reconstructions like this required all sorts of information including ice sheets, micropaleontological data, and vegetation patterns.
In this paper, Bernabo and Webb provide the first paleoclimatic reconstruction with pollen data in the northeastern United States, where effects of climate change can be well-traced throughout the Holocene. The pollen studied are from spruce, pine, oak, herbs, and the BAFT group (representing the boreal forest, conifer-hardwood forest, deciduous forest, the prairie, and northern hardwoods, respectively). By mapping pollen occurrences through time, Webb and Bernabo get a broad sense of vegetation dynamics and responses to climate change in the area.
Vegetation patterns were mapped from 11, 000 BP to present, each over 1000 years. Pollen was collected from 62 cores, both published and unpublished data, from around the northeastern United States. Isopoll, difference, and isochrone maps were constructed for comparison of vegetation ranges through time. Vegetation patterns were mapped along with paleogeographic features like ice sheets, glacial lakes, and shorelines so that a more well-rounded overall picture of paleoenvironment could be seen at each time.
The results show the shrinking and redevelopment of a boreal forest; expansion of pine followed by the replacement by oak; the changing composition of deciduous and conifer-hardwood forests, along with the expansion of the BAFT group within the latter; the westward retreat of prairie and forest following 7000 BP; and increase in herbs following the immigration of Europeans. These pollen changes or migrations can be related to changes in glacial conditions; a decrease in pollen variability (i.e., an increase in vegetation stability) occurs around 7000 BP, correlating with the disappearance of the Laurentide ice sheet.
This paper likely helped Webb and his colleagues develop COHMAP (Cooperative Holocene Mapping Project), an interdisciplinary project similar to CLIMAP that looked not only at the LGM, but also at the interglacial conditions that followed. The authors provide a few reasons for the movement of vegetation (glaciation and deglaciation, immigration of new taxa, further development of already-present taxa) - maybe think about what other factors could be affecting the patterns seen here? Could there be anything biasing the data?
Woah, site looks different. My keyboard is still broken, so I'll mostly save my thoughts for class. But I will ask one thing: how do they account for changes in wind patterns? Like, if to the left of your lake you've got a grassland and to the right you've got a boreal forest and the wind prevailingly blows to the right, you'll get a 'grassland' signal, But what if, after 1,000 years of blowing to the right, the wind shift and starts to mainly blow to the left? Then you'll start getting a 'boreal forest' signal, even if there's no actual change in vegetation. Maybe wind currents around lakes change infrequently enough that this doesn't matter? Maybe they corrected for this somehow and I just missed it, or it was in the supplementals? I'm sure you guys'll know.
ReplyDeleteI second what Lucius is saying about the differing wind patterns altering what is accumulated. I would also think that potential biases to the data would be the prevalence of pollen from different plant types (r vs. K selection) or if different morphotypes of pollen have slightly different diagenetic histories (insert taphonomic mega-bias here).
ReplyDeleteOne of the things that kept coming to my mind when reading this paper was: Where they obtain the pollen from and how do they actually quantify it? Which types of tools researchers had in 1976 to quantify that and how precise were they? And all these questions can be related with what Lucius was saying about the wind… Did they account for things like that?
ReplyDeleteAlso, another thing that I missed was more more numerical summary tables (there is only one plot at the beginning of the paper and it’s not very helpful in my opinion). I think that the idea of using maps is a great idea and it really helps to understand visually how vegetation changed through time, but I would have cut down in maps (maybe add more information in each one of them) and include some numerical tables instead and even some more graphs to get a better idea of the data they were dealing with. What do you guys think?