Paper 27

Paper 27

Blog Author: Alex Shupinski

Authors: Christopher Bernabo 

Thompson Webb 

I received a botany degree from Swarthmore and a PhD in atmospheric sciences from the University of Wisconsin-Madison. In 1972, I joined John Imbrie and R.K. Matthews to study Quaternary climates, as CLIMAP was starting. I added a terrestrial paleoclimate and paleovegetation focus to their paleoceanographic perspective on earth system history. Once COHMAP (Cooperative Holocene Mapping Project) began in 1977, I worked with colleagues at Wisconsin, Minnesota, Oxford, Durham, Lamont, Brown, and Oregon to compile large data sets, to interpret them in climate terms, and to compare the results with climate-model simulations of the past 21,000 years. Key results appeared in Science in 1988, in a joint-edited book in 1993 and in an issue of Quaternary Science Reviews in 1998. In 1996, I and Jeff Donnelly began studying the sedimentary record of land-falling hurricanes. I retired in 2005 and continue teaching in Summer and Continuing Studies at Brown.

Introduction

-Pollen data was mapped in northeastern North America 

-Studying Holocene vegetation

-Five categories: pine, oak, spruce, herbs and BAFT group

The Data Base

-Data was obtained from published sources

-computer programs calculated the pollen percentage data

-300 pollen types identified

-Radiocarbon dates on cores determined depth, most cores had sediments throughout the Holocene

-Average of four dates per core

-62 sites with the greatest changes occurring between 11,000 and 7,000

Construction of the Maps

-Isochrone maps show the movement of pollen species and a time period

-Isopoll maps demonstrate patterns in the pollen frequency across the distribution

-A sequence of events was created 

-Maps were created of modern distributions for the identified pollen and then a numerical comparison was used using Pearson product-moment correlation coefficient

Description of the Holocene Pollen Maps

-Spruce reduced in abundance around 11,000.  Pine increased in northern regions, oak increased in the southern regions. Spruce no longer dominated and herb pollen was reduced showing a more closed forest.

-10,000 the spruce was replaced by pine.  By 9,000 it was no longer a major pollen found and by 8,000 it was a minor element of the region

-Laurentide ice sheet collapsed around 8,000 and spruce pollen was gone from the south  and pine and oak shifted farther north.

-As time continued the change in pollen patterns was more gradual up until 4,000.  BAFT pollen  increased at the expense of pine changing.

-Between 4,000 and 2,000 the gradient between arboreal and nonarboreal pollen increased in the Midwest.

-Up until 500 right between vegetation changed due to European settlement the vegetation tended to change only on a local level.  Since this time the vegetation change is mainly due to human activity. Herbs increased due to agriculture.

-Final glaciation showed the greatest change in pollen movement.

Four Major Changes

-Spruce declined

-Pine moved westward, beech and hemlock moved to the great lake region around 8,000.  Hardwood forests shifted north. 

-Hemlock, Birch, Maple and Beech all expanded their ranges.  BAFT becomes dominant in New England

-Prairie development occurring the Midwest over 11,000 years ago and began to move east around 10,000 to 9,000 and then receded westward up until 2,000

Conclusion

-Major vegetational shifts and patterns were able to be tracked using the pollen data

-Mixing of pollen in the air took away fine scale changes and taxonomy was general

-The cartographic approach provided visual aids to demonstrate the patterns

-Areas of steep gradients in vegetations should be studied more closely with more densely spaced sites

-This study will provide a framework for future studies to better understand the vegetational history of North America

Thoughts: 

The authors recognized the flaws in the strategies they used but provided more types of criteria to be used and combined when analyzing pollen data which is important in understanding the entire ecosystem of North America.  This paper would help to improve future studies looking at pollen data. I also felt it was very well-written and easy to follow, which is important for any paper to be influential. The methods was a bit boring to read but I think the level of detail we can obtain is fascinating and the history of our vegetation is very interesting to me.