Guest Bloggers – SEAK25: On the third and final day in Angoon, we split into two groups. One climbed Hood Bay Mountain to extract high-elevation mountain hemlock cores, the other kayaked to Turn Point, searching for and coring culturally modified trees (CMTs).
The CMTs at Turn Point are Sitka Spruce that have distinct scars with hack marks, evidence of previous Tlingit generations harvesting sap and fire starter. These CMTs are of heightened interest because a new hydroelectric power plant is soon to be built, and its road will require the removal of many trees in Turn Point. High school students in Angoon have already worked to preserve the CMTs by creating photogrammetric renderings. This work will prevent the information from there valuable trees, which connect locals to their lineage, from being lost altogether. We hoped to contribute to the effort by extracting cores to investigate their growth and date the scars using tree rings.
A map showing Turn Point in relation to Angoon. Turn Point will be the site of a hydroelectric plant for power generation for Angoon, which is now powered by a diesel generator.
We embarked on this mission in the morning, leaving from the seaplane dock on kayaks. We had
Dendrochronological methods are a key part to our research team’s success. While analyzing and drawing conclusions from data is essential, it is equally as important to ensure the proper collection, preparation, and handling of samples and extraction of ring measurements. There are many key steps to this process in dendrochronology, that when done correctly, ensures the success of a research team.
Taking samples
Tree cores are extracted using an increment borer. By manually drilling the auger into a tree, the core is preserved inside the increment borer with minor injury to the tree. The core extractor, a half circular metal tray, then fits into the auger bit. After cranking the handle counter clockwise, the core then fully separates from the body of the tree. Pulling the core extractor out of the auger allows the extraction of a tree core.
Increment borer.
Selecting the right tree within a stand is crucial to obtaining a good sample. It is important to consider factors such as tree health and direction of lean before coring. Trees that lean excessively can be more difficult to core, as the wood is under more directed pressure. We aimed for trees that stand tall, with little to no lean. If there is
Guest Blogger: Lynnsey Delio, The Keck Geology 2025 team has been working in the Wooster dendrochronology lab for the first week of research. The team cored the oak tree in front of Scovel on day 1 for some practice coring. They also made use of the woodshop in Scovel Hall and practiced sanding and mounting cores.
Dexter, Lynnsey, Lev, and Landon coring the oak tree in front of Scovel Hall.
Lev with a core reveal!
The team has also been working with programs COFECHA and CooRecorder in the computer lab to mark the tree rings on red cedars from Southeast Alaska. They have been working to create an optimized red cedar tree ring series for the area, dating back centuries. This data can be used to compare to other tree ring series and look for climate signals and responses. These climate responses can be analyzed from a global climate perspective to understand the correlation between dendrochronology and global climate phenomena.
To accurately date the cedar cores, the team used cores from previously dated red cedars in Southeast Alaska to correlate them to the undated samples. Some of these previously dated cores included logged trees that were intended for use in totem poles.
Figure 1. Title page of Amanda’s thesis including one of the key figures.
Amanda Flory (class of 2025) completed a thesis that investigated the interplay between the pace of the ocean-atmosphere climate in the Northeast Pacific that is dominated by Pacific Decadal Variability along with the volcanically-forced coolings inferred from tree-ring records. Her title page (above) summarizes the results with several known volcanic intervals linked with decade-long coolings. These coolings are inferred from a tree ring-width series located in coastal Southeast Alaska (Dude Mountain, Ketchikan, Alaska). In addition to her thesis work Amanda presented her results at the meeting of the Geological Society of America in the Spring of 2025. The take-home here is that the variability as recorded in the tree-ring record appears to be a combination internal variability of the Northeast Pacific [1] and volcanic forcing [2] contributing to the decadal variability in the climate.
Figure 2. The author (left) cores a yellow cedar (Cupressus nootkatensis) – Nick (middle) and Proto provide support.
Figure 3. Comparisons of Sitka, AK temperature records for the months of December through October of the growth year correlated with the Dude Mountain ring-width record.
This climate/tree-ring comparison (Figure 2) examines the moving correlation over time (since
The lead author of this work, Fred (Wenshuo) Zhao, photographed in front of the Mendenhall Glacier in Juneau, Alaska. The logs at his feet, recently exposed by the retreating ice, are the subject of his undergraduate thesis and this publication. The College of Wooster Tree Ring Lab has an extensive collection of subfossil wood (trees run over in the past by glaciers) and this wood is often stained by exposure to the elements altering the color of the wood. This alteration inhibits the measurement of tree-ring parameters like blue intensity measurements. Measuring blue intensity (BI) has been shown to improve climate reconstruction and improve general tree-ring dating (Wilson et al, 2017, 2019). Fred, with the great help of Junpeng Fu and Nick Wiesenberg at Wooster, chemically treated the wood showing an improved climate signal in the BI measurements after treatment. This paper describes the process and evaluation of this chemical method using wood sampled from along the Gulf of Alaska as an example.
Degrees C
One of the clever tests that Fred performed to evaluate the improved climate signal was to compare climate signal of latewood blue intensity measurements before soaking in hydrogen peroxide (graph on the left) and after soaking (right)
Learning about environmental change from tree rings
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