Wooster Geologists

Guest Bloggers SEAK25 (Keck – Southeast Alaska 2025) – 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 a slight lean, then we cored perpendicular to the direction of the lean. When coring we were sure that the auger aimed to the heart of the tree and did not enter at an angle. Depending on the thickness of the tree, two separate cores are required to get data on the entire diameter of the tree. Smaller trees may only require one coring through the full diameter.

Storing and labeling samples
After extracting cores from trees, samples must be properly stored and labeled. The cores are carefully removed from the extractor tray of the increment borer storing the in a plastic straw. It is important to keep the end of the straw near the opening of the auger to ensure the entire core is preserved in case the core itself is broken and is extracted in multiple pieces. Once the sample is safely inside of the plastic straw, the straw ends are folded in to keep the sample in place. The plastic straws we use have holes throughout for proper drying of the sample.

Plastic straws used for sample storage.

It is critical to label the samples immediately after putting them in the plastic straw to avoid mislabeling and confusion. Samples are labeled by their tree ID. This tree ID is given based on research location and sample number. The red cedar cores from Klawock, Alaska were from the “Lower Steelhead” site. They were marked with the label LSRC, standing for “Lower Steelhead Red Cedar.” Each tree from the site was assigned a number as it was cored,;LSRC01 was the first tree cored. The label is written directly on the plastic straw to keep the samples organized. Assuming there are two cores from each tree, each core should have both an “A” and “B” sample, taken from opposite sides of the tree. If they are stored in separate straws, “A” or “B” should be written after the tree ID (eg. LSRC01 A). If it is not clear which end of the core is which, labeling the inside “pith” could also be helpful for future analysis. Tree IDs are used during the marking and cross dating process to identify particular cores, so accurate identification is important.

Once the samples are labeled and stored in the straws, they can be taken back to the lab where they will air dry inside of the plastic straw for anywhere from a couple days to several weeks. Having a fully dried core will lessen the likelihood of warping or cracking when it is glued to a mount.

Prepping core samples for analyses
Once the cores have been dried, they are placed in wooden core mounts. Cores are glued into the mounts with the grain of the wood oriented vertically. The cores are then secured using tape every 2 to 3 inches. The mounts are then labeled with the sample name. Once the samples are mounted they are ready to be sanded. This process begins with placing the core upside down on the belt sander. The core is first belt sanded on 80 to 150 grit then 180 to 220 grit. The cores should be sanded approximately to the thickness of a quarter above the line of the wood mount. The samples are then hand sanded depending on the softness of the type of wood. For example, yellow cedar is harder than red cedar so it was hand sanded using 600 grit then 800 grit sandpaper. Red cedar is softer so it was hand sanded with 800 grit.

Mounted and labeled cores.

A sample after being belt sanded.

Scanning samples
Once the sanding process was completed, and the wood anatomy was clear and scratches were removed the cores are ready for scanning. We used a flatbed photo scanner to scan the cores (2400 dpi). The scanned images were then uploaded to CooRecorder, a software used for tree-ring dating and analysis (Maxwell and Larsson, 2021). CooRecorder allows users to click and place a point on the boundary between each ring, capturing annual layers within a tree. We placed points on the earlywood-latewood boundary, capturing the end of each growing season. This boundary can be identified by the distinct changes in color between latewood and earlywood, latewood being tighter-grained and darker than the more porous and lighter-colored earlywood. We then measured the distances between ring boundaries (individual ring thicknesses). A master ring-width chronology of red cedars already in hand from the area (our master chronology) was used as a dating reference. Given that cores we measured and the series in the mater chronology were from the same region and experienced the same climate signals, we expected the widths to match to some extent. This is an an important step in recognizing any mistakes in dating or any unusual growth in the trees. The CooRecorder software can also display the latewood blue intensity, which is shown in the image below (a subject for a later blog post, blue intensity is a fascinating parameter that we are excited to analyze later this week). The final step for each core was ensuring the latewood blue boxes were parallel to the ring thus accurately representing the boundaries of each ring. Overall, the dating using CooRecorder is a tedious yet rewarding process, and upon completion, we had dates and ring-width measurements for each core and could proceed to chronology development.

Screenshot of the CooRecorder software with the latewood blue intensity parameter turned on.

Quality Control of the Cross dating
Another important step in the dendrochronological process is the building of a “master” chronology. A master chronology is a collection of tree ring series of a particular species that is generally accepted to be a reliably dated and can be compared with newly measured ring – width series. In our case we added to the master chronology which was then used to evaluate the climate signal in the trees.

An example run that compared two of our Western red cedar chronologies, using the COFECHA program (Holmes 1983). 

For example, an existing Western redcedar master chronology may be used to check the reliability of a different red cedar chronology from a similar area. This is accomplished by comparing the relative growth of the trees over time. If the chronologies display a similar growth pattern as measured by correlations (i.e. years of faster and slower growth are during similar years), then the new chronology can likely be trusted as being a well-dated and potentially useful dataset. This process of cross-referencing an existing chronology with a new one is called cross dating, and is an important principle in dendrochronology. Our research team has built a new master chronology for Western redc edars using the program COFECHA (Holmes, 1983) that consist of 60 ring-width series. To our knowledge, this is the most robust and complete chronology of red cedar in Alaska to date. Thus, this is an exciting opportunity to use this new chronology for potentially innovative projects.

Preliminary investigation of the ring width series
Once samples have been properly collected and prepared for analysis, a preliminary investigation of how the data might be useful can be performed. Before identifying the scope of a study, one needs to know what phenomenon in particular the tree ring chronology is being used to study. This is easily accomplished by loading a tree ring chronology and comparing it with an existing observational dataset. Often, in dendrochronology, this will be a climatic data set (average, minimum and maximum temperatures, precipitation, etc.) because trees are the most sensitive to climatic variables. However, finding which climatic variable a particular chronology is sensitive to can be trickier.

A correlation field demonstrating the high correlation between our Western red cedar chronology and winter minimum temperature in Alaska. Note the high positive correlations of the tree-ring site and much of Alaska and Western Canada.

To accomplish this, our research team loaded our master Alaskan red cedar chronology into an online climate analysis tool called KNMI Climate Explorer (Trouet & Van Oldenborgh, 2013), a useful website that contains a plethora of observational and modeled climatic datasets. This website also allows the user to correlate  datasets, which is how our team, through trial and error, found a climatic variable that our chronology is sensitive to. For this particular red cedar chronology, we found that the chronology is sensitive to winter minimum temperatures. This means that our chronology dataset has a high positive correlation with the observational dataset for this particular variable. The team is working on understanding why winter minimum temperatures are most strongly correlated with the site.

Red cedar chronology (red) the blue line is the sample size. The 1876 ring is the most narrow of the record. Note the increase in tree growth over the past century.

Next steps
Now that we have identified a climatic variable to which our chronology is sensitive, our team can begin more detailed analysis of the chronology. Each of the SEAK25 Team will pick a more narrow topic on which to complete an in-depth research project throughout the course of the summer and the following school year. Potential projects might include an evaluation of the evolution of the Aleutian low-pressure system, an investigation of the Indian Ocean teleconnection recognized in western red cedar, a reconstruction of Great Lakes water levels, and possible snowpack reconstructions in the Sierra Nevada.

References cited
Holmes, R. L. (1983). Computer-assisted quality control in tree-ring dating and measurement, Tree Ring Research, v.43, 69-78.

Maxwell, R. S., & Larsson, L. A. (2021). Measuring tree-ring widths using the CooRecorder software application. Dendrochronologia, 67, 125841.

Trouet, V., & Van Oldenborgh, G. J. (2013). KNMI Climate Explorer: a web-based research tool for high-resolution paleoclimatology. Tree-Ring Research, 69(1), 3-13.

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 1857) is based on a running 35-year correlation. Correlations change from positive (blue) to negative (red) and back to positive. This non-stationary response temperature is puzzling and is likely complex reflecting the ecological and climate-related thresholds at the site. Amanda explored the correlation between ocean heat content ([3]; see Figure 1: title page) and tree growth. The strong and steady relationship between the ocean heat content and growth suggests that the near-coastal tree-ring site is dominated by the ocean-atmosphere system immediately offshore.

Figure 4. Key volcanic events that correspond with decades of cooling.

As is the case with most theses, more crucial questions are raised and will continue to be investigated. These include continuing the examination of the yellow cedar climate response as well as applying new analyses that seek to tease out the volcanic response from the internal response of the Pacific Decadal variability in the record.

Acknowledgements: This work was supported by the National Science Foundation Grant AGS-2002454. We would like to thank Klawock’s Alaskan Youth Stewards (AYS) group for their expertise and guidance while conducting field work.

References:

[1] Schneider, N., and Cornuelle, B.D., 2005, The Forcing of the Pacific Decadal Oscillation:, doi:10.1175/JCLI3527.1.

[2] Wang, T., Otterå, O.H., Gao, Y., and Wang, H., 2012, The response of the North Pacific Decadal Variability to strong tropical volcanic eruptions: Climate Dynamics, doi:10.1007/s00382-012-1373-5

[3] Levitus, S. et al., 2012, World Ocean heat content and thermosteric sea level change (0–2000 m), 1955–2010: Geophysical Research.

Guest Blogger Grace Neuman: From mossy bogs to forgotten fields, the landscape of Northeastern Ohio holds buried stories. My Independent study, examines how two centuries of post-settlement human activity have altered the region’s ecosystems, and how we can still see those imprints today.

I investigated various ecological and historical data sources, such as tree rings, sediment cores, soil textures, soil chemistry, and radiometric dating, to trace land use patterns and forest disturbance over time. These scientific methods helped uncover both natural and human-driven shifts in the region’s environmental conditions.

Me in the lab with sediment grain size analysis equipment (PARIO).

My work focused on Brown’s Lake Bog Preserve, located on Browns Road in Shreve, Ohio. This Nature Preserve harbors remnants of Ohio’s post-glacial ecosystems and is one of the last few acidic bog ecosystems remaining in Ohio. The LiDAR map above shows the location of the Bog (BB) and the lake (BL). This kettle lake is surrounded by kames.

Sediment core (left) and various measurements (right) provided by Erika Freimuth. The sediments here record the transition of the surrounding landscape from an organic-rich bog (black mud) to a brighter clay/silt blown into the bog when the land was cleared. This profound change took place about 1820 dated by Pb-210. The blue line on the left is magnetic susceptibility and tracks the increase in eroded soil to the basin whereas the red line (organics) decreases.

The gain size analysis of the sediment deposited in the basin closely after 1820 is composed of mostly clay and silt. This grain size is consistent with eroded soils from the surrounding farmed landscape.

The dating with Cesium-137 and Pb-210 by Dr. Josh Landis of Dartmouth College yielded interesting results.  The disruption about 1950 in the graph above suggests erosion and and increase in mass accumulation of sediment likely linked to logging in the basin.

Within the Preserve is a white oak stand of trees growing on the kames. These trees were witness to the land use changes. The release in tree growth about 1820 is consistent with the inferred land use change, also not the bump in ring-widths about 1950 when the forest was again selectively logged.

One of the classic kames surrounding the bog. This work was supported by the National Science Foundation and the Copeland Fund of The College of Wooster. We thank The Nature Conservancy for management of the site and permission to core the lake. Thanks also to T.V. Lowell for procuring the core and N. Wiesenberg for his help in the lab.

The link to the full publication and supporting data can be found here.

HBI Wizard, Aaron Diefendorf (University of Cincinnati) on the forest edge of Browns Lake, Wayne County Ohio. Dr. Diefendorf and Dr. T.V. Lowell and their students (Dietrich, 2023; Corcoran et al., 202o; Freimuth et al., 2021) are the force behind investigating biomarkers secreted from diatoms in lake as records of past precipitation changes. This basic research is impressive given they are chasing molecules (shown below) that are secreted from microscopic diatoms in lake waters and in complex organic sediments that accumulate at the bottom of lakes. Wooster Geologists have participated in the field monitoring and diatom work resulting in several Independent Study projects.

Diatom-derived highly branched isoprenoids (HBIs) are lipid bio- markers found in marine and lacustrine sediments. Most of the work on these has been done in marine environments and the UC group is now extending study to lake settings.

The sampling team on a North Dakota Lake.

Locations of the 50 lakes sampled in this study (A) and expanded maps of the Indiana lakes (B) and Adirondack region lakes (C).

The University of Cincinnati team and collaborators from St. Lawrence University coring on an Adirondack lake on a spectacular fall day. T.V. Lowell (orange gloves) is the core boss who has provided “high-quality” mud from the bottom of lakes and bogs across the planet and for several Wooster classes and student theses.

References:

Last Monday there was a power outage on campus and classes were cancelled, despite this news our afternoon lab period fieldtrip went on as planned. The trip consisted of a field trip led by Nigel Brush (retired from Ashland U. and Wooster). It was a great trip on a beautiful day and we greatly appreciate Dr. Brush’s time and willingness to share his expertise of the history of our region. 

Above the students survey ice stagnation features from the top of a kame.

View of a kettle from the rim of the kettle. The kettle is located on the map below (lower right).

Map (soilexplorer.net) showing the kame and kettle terrane with the esker in the middle. The kame shown in the photo above is the circular feature in the lower right.

The Mohicanville Dam is located in one of the former Lake Craigton spillways. The dam, located in this hours glass spillway, is the site of the narrowest reach of the gorge and controls floodwaters that would otherwise inundate communities to the south. Extensive flooding in 1913, in part, prompted the US Army Corp. to build this and other flood control structures.

GoogleEarth image of the Mohicanville Dam.

Map above (from soilexplorer.net) the amazing stagnant topography of the Browns Lake Bog area. Now that Dr. Brush pointed out some additional features in the region we wonder is the feature in the upper left is an esker?

The group at Browns Lake Bog discussing the old growth forest on the kames and the relatively new forest in the flats. The the post-glacial history recorded in the sediments and tree-rings at the site has been an extensive subject of research at the College of Wooster in collaboration wit hthe University of Cincinnati over the past two decades.

The upshot of the bog ecology is that during the time of European Settlement lake core records show a pronounced influx of silt and clay from surrounding soils and the fertilization of the nutrient-limited bog allowing the establishment of vascular plants (trees and shrubs) and the setting that we see today. This model was originally put forth by by Ireland and Booth (2012) and is the subject of Grace Neuman’s (’25) IS project (blog coming soon).

Reference: Ireland, A.W., Booth, R. K., 2012, Upland deforestation triggered an ecosystem state-shift in kettle peatland: Journal of Ecology, vol. 100, p. 586-596. 

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.

Paleoclimate class (2021) at Johnson Woods Orrville Ohio. One of the key sites in the paper and one of the key sites in the Midwest. Originally cored by Ed Cook (Lamont-Doherty Tree Ring Lab) in 1980, the site has been updated by The College of Wooster Tree Ring Lab and by Justin Maxwell at the Indiana University Tree Ring Lab. Students sampling the remanent white oak stand at Browns Lake Bog a site managed by the Nature Conservancy. 

Coring the second-growth white oaks in Wooster Memorial Park.

Another second growth site is within the Wooster city limits at the Kinney Field Park.

The College of Wooster campus maintains an impressive stand of old growth white oaks on its campus. Here members of the Holden Arboretum Tree Corps sample one the the impressive old trees.Secrest Arboretum (on the Wooster campus of the CFAES) is one of our favorite sites to cores trees. Many of the trees from  all around the world have lived in Ohio for over 100 years. Here one of the coauthors cores a white oak planted about 100 years ago.

A final word on this study. Future warming in the Midwest is projected to see increases in spring precipitation, likely decreases in late summer precipitation, which if coupled with an increase in maximum summer temperatures would increase the moisture stress on these trees. Our examination of these varying climate responses with respect to site characteristics and forest age can help future assessments of tree health and the forest’s ability to sequester carbon, as well as facilitate efforts to reconstruct climate by using a range of tree sites for intervals when sensitivity in old growth sites is lost.

These data from the sites in Northeast Ohio are available in the International Tree-Ring Databank maintained by NOAA and many of these records have been incorporated into the North American Drought Atlas contributed to the larger climate science community by Ed Cook and colleagues.

References:

Acknowledgements: This work was funded by The College of Wooster, NSF Geopaths and NSF – EAR 2039939 grants.