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)
The College of Wooster Tree Ring Lab faculty, staff and students have teamed up to publish results of an analysis of a network of tree-ring sites in Northeast Ohio to ask the question what is driving the changing climate response of the trees. The tree-ring sites include young (100-year-old) white oaks in Secrest Arboretum, Wooster, two sites of post-settlement age (about 200-years old) from Wooster Memorial Park and The Kinney Field Park both in Wooster and four old growth sites (>300 years old) from some of our favorite sites including The College of Wooster campus, Cornerstone Elementary, Browns Lake Bog, David Kline’s (the author) old growth forest on his farm and Johnson Woods the largest tract to old growth white oak forest in Ohio.
The upshot of the study reveals that the one- hundred-year-old white oak stand in Secrest Arboretum, along with two second growth stands have consistently responded positively to summer (June-July) precipitation over the past century, whereas the four nearby old growth sites have lost their moisture sensitivity since about the mid 1970s. This “fading drought signal,” which has been previously reported by Maxwell et al. (2016), appears to be more a result of the legacy of land use
Learning about environmental change from tree rings
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