Students core hemlock trees to understand past climate

November 10, 2014
Coring old growth hemlocks
Coring old growth hemlocks

PLATTEVILLE, Wis. — Sara Allen, lab manager and research associate of the Tree-Ring, Earth and Environmental Sciences Laboratory at the University of Wisconsin-Platteville, and three students from UW-Platteville recently took a trip to the Upper Peninsula of Michigan to collect tree-ring samples from old growth hemlock trees. The trip was part of an ongoing research project to update tree-ring chronologies across the Great Lakes region to help improve understanding of the forests’ past climate and environmental history, which in turn will improve understanding of future climate scenarios.

The researchers included Allen; Giselle Varrientos, a senior geography major with a soil and crop science minor from Kenosha, Wis.; Derek Scoville, a junior mechanical engineering major from Kenosha, Wis.; and McKaylee Duquain, a senior forestry science major at UW-Madison and enrolled member of the Menominee Nation. Allen’s daughter Shea provided assistance as photographic support.

This field work contributed to a larger project that emerged from a collaboration with the College of Menominee Nation Sustainable Development Institute and with the help of Dr. Ed Cook, a world-renowned climate change scientist from the Lamont-Doherty Earth Observatory Tree-Ring Laboratory at Columbia University in Palisades, N.Y.

The project began in the summer of 2012, when Dr. Evan Larson, director of the TREES Lab, led a collaborative research project that supported students from UW-Platteville and CMN with funding from the Wisconsin Alliance for Minority Participation to update tree-ring chronologies originally developed by Cook in the 1980s. The research conducted through the WiscAMP grant successfully updated the targeted chronologies and introduced students to the science of dendrochronology, but had the added result of identifying a strong relationship between summer temperatures and the growth of hemlock trees in northern Wisconsin and the Upper Peninsula of Michigan.

“What we found is that hot summers stress hemlock trees to the point that the next year they lay down a very narrow ring,” said Larson. “Going back in time, narrower rings mean warmer summers and wider rings indicate cooler summers.”

On this trip, Allen, Varrientos, Scoville and Duquain identified one site each in the Ottawa National Forest, Hiawatha National Forest and Sault Sainte Marie State Forest Area in upper Michigan using maps that Cook had developed. Then, using an increment borer, a hand-turned tool that is essentially a very long hollow drill, they extracted two cores of wood from each of the 30 trees that included the history of the sampled tree through records of annual growth.

The researchers are now examining, recording and analyzing data from the core samples in the TREES Lab using dendrochronology, the scientific method of assigning exact calendar dates to the annual growth rings of trees and analyzing patterns of tree-ring width to gain insight about past environmental conditions.

“Studying the tree rings in hemlocks is an incredible look into the past because the rings provide information about climate going back hundreds of years,” stated Allen. “Hemlock growth is sensitive to their growing environment, so developing chronologies based on their ring-width data allows us to reconstruct summer temperatures which, in turn, are related to fluctuations in the level of lakes across the Great Lakes Region, including the Great Lakes themselves. This climate history can help us better understand current climate trends and the impact they can have on our environment.”

“This research opportunity reinforced my desire to be a geographer,” said Varrientos. “Trees are excellent sources of information and this research can contribute substantial information to society about the past, and what this might mean for the future.”

“This research experience was an incredible experience,” said Scoville. “It opened my eyes to the value that trees bring to us. Trees are so much more than a resource. They tell us a story about the land.”

“The areas where we collected cores are some of the last old growth patches of hemlock in the Upper Peninsula of Michigan,” said Allen. “Seeing all of the logging operations reinforced how special it is to have old growth and how important it is to preserve what little old growth we have left.”

“The Great Lakes Hemlock project is a beautiful example of how exciting results can emerge from what at first was fairly basic research,” said Larson, “and how this type of hands-on research experience can effectively engage students from a range of backgrounds and interests.”

To date, eight UW-Platteville and CMN students have contributed to this project. Students have been lead authors on four presentations at regional and national professional conferences, with Scoville and UW-Platteville geography major Gabriel Brownell slated to present additional results at the 2015 Annual Conference of the Association of American Geographers in Chicago, Ill., next April.

Written by: Connie Spyropoulos, College of Liberal Arts and Education, 608-342-6191,, and Laurie Hamer, College of Liberal Arts and Education, 608-342-6191,


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