Hi, my name is Claire Cerne and this is my first blog post for the summer of 2020. I am a student research assistant for Greg Wiles at The College of Wooster. The blog I created is dedicated to highlighting research topics throughout this summer. I am working alongside another classmate to help analyze tree ring data and educate a group of young scientists living in Hoonah, Alaska.

Before the stay at home order due to the COVID-19 pandemic, Dr. Wiles, Dr. Ben Gaglioti, Dr. Dan Mann, and several students and I had plans to visit Alaska. I would be going to Dagelet Glacier to collect tree ring samples with Dr. Gaglioti and Mann. We were planning on taking a two-week trip (weather permitting) that would have been in the late May/ early June months. Unfortunately, this trip had to be canceled.

After the plans fell through, Dr. Wiles offered me and another classmate, Julia Pearson, a position for the summer that would focus on science education. We would work with the TRAYLS group in Hoonah, Alaska interested in the environment and add to their lesson plans with presentations. In our first Microsoft Teams meeting, we started with introductions, the basics of dendrochronology, and how to core a tree. The TRAYLS group has begun the tree coring process and once this is complete, they will be sending the cores to the College of Wooster. The cores will be scanned and we will begin analyzing. After this is complete, we will relay the information about the trees they collected cores from. In the mean time, Julia and I will give access to maps and presentations to teach the group about topics like the Little Ice Age, what happens to a tree when it is stripped, and the story of Glacier Bay.

This summer research position heavily relies on Microsoft Teams meetings, shared Google slides, and an open schedule for meetings during the week. Communication is key in this process and I am learning how to better communicate like asking more about certain topics or where I can find information if I get stuck. We had a meeting with one of Wooster’s science librarians, Zach Sharrow, to help us find academic sources from home. I have also had to learn to be more independent while working from home, how to create a work environment, and a create schedule that works with the rest of my family’s schedules. Adapting to working at home will be a summer-long process but with the support of Dr. Wiles and Julia, we will make an awesome final product with the TRAYLS group.

This work has been funded in support by the National Science Foundation. The grant that was received is the AGS 8001184 –RUI: Collaborative Research: Extending key records of Holocene climate change and glacier fluctuations in the North Pacific region using subfossil wood from Southeastern Alaska.

The Wooster Tree Ring Lab has just published a paper with Franklin and Marshall College and The Ohio State University on the climate response of the Dawn Redwood tree. The study site is the beautiful Secrest Arboretum at the OARDC – OSU Wooster Campus. The upshot is that these remarkable and fast-growing trees are clearly doing well and as long as the increase in precipitation that Northeast Ohio is receiving keeps pace with the summer warming they should continue to do well. Why not plant more of these beautiful trees as they thrive, sequester carbon, and provide many other ecosystem services.

The senior author is Lauren Vargo, who is now a glaciologist research scientist at the Antarctic Research Centre in Wellington, Australia. Lauren did much of this work while an undergraduate at Wooster. Lauren is also the recent lead author on this Nature Climate Change contribution.

Here is the technical abstract of the Dawn Redwood paper:

ABSTRACT

Figure above shows the tree-ring record from a stand of 19 Dawn Redwood trees (upper panel A). The lower blue and red graph (B) is the climate response of the trees – temperature (red bars) is strongly negatively correlated with summer (June and July) temperatures and with February temperature. The summer relationship makes sense as hot summers require higher evapotranspiration demands. The negative correlation with winter is hypothesized to be linked to warming winters leading to less snow cover leaving roots exposed and vulnerable to damaging frosts. This negative relationship may go away as warming continues and frosts become less frequent.

Figure above shows three photos of cores from Dawn Redwood – note the narrow 1988 drought ring (white dots). 

The College of Wooster Paleoclimate class mulls around the Dawn Redwood stand. 

Another great photo of  Dawn Redwoods – they are deciduous conifers so this photo in the early spring before growth.

Many thanks to the Secrest Arboretum for permission to core these impressive trees. We greatly appreciate the support of Jason Veil the Curator of the Arboretum.

Four new studies from the Wooster Tree Ring Lab have recently appeared in Ecology, Journal of Geophysical Research – Biosciences, The Holoceneand Chemosphere.

Brian Buma lead the study published in Ecologythat described the results of revisiting a classic ecological succession site in Glacier Bay National Park and Preserve. The article is titled: 100 years of primary succession highlights stochasticity and competition driving community establishment and stability. We blogged about some of the fieldwork for this study a few years ago here.

Abstract: The study of community succession is one of the oldest pursuits in ecology. Challenges remain in terms of evaluating the predictability of succession and the reliability of the chronosequence methods typically used to study community development. The research of William S. Cooper in Glacier Bay National Park is an early and well‐known example of successional ecology that provides a long‐term observational dataset to test hypotheses derived from space‐for‐time substitutions. It also provides a unique opportunity to explore the importance of historical contingencies and as an example of a revitalized historical study system. We test the textbook successional trajectory in Glacier Bay and evaluate long‐term plant community development via primary succession through extensive fieldwork, remote sensing, dendrochronological methods, and newly discovered data that fills in data gaps (1940’s to late 1980’s) in continuous measurement over 100+ years. To date, Cooper’s quadrats do not support the classic facilitation model of succession in which a sequence of species interacts to form predictable successional trajectories. Rather, stochastic early community assembly and subsequent inhibition have dominated; most species arrived shortly after deglaciation and have remained stable for 50+ years. Chronosequence studies assuming prior composition are thus questionable, as no predictable species sequence or timeline was observed. This underscores the significance of assumptions about early conditions in chronosequences and the need to defend such assumptions. Furthermore, this work brings a classic study system in ecology up to date via a plot size expansion, new baseline biogeochemical data, and spatial mapping for future researchers for its second century of observation.

Photo taken in the West Arm of Glacier Bay close to where the Cooper plots were “rediscovered” by Buma and others.

Dr. Ben Gaglioti (University of Alaska – Fairbanks) and collaborators just published another innovative study. This time Ben has assembled a time series of traumatic resin ducts (TRDs) in mountain hemlock that  is a record of past winter conditions and the strength of the Aleutian Low. The article appeared in the Journal of Geophysical Research: Biogeosciences.

The study included tree-ring records from four wild outer coast sites along the the Gulf of Alaska. This is the first work to use these TRD features in tree-rings as a proxy for winter storminess.

a – The clearly-stressed trees used in this study. b – Careful observations and measurements from increment cores were taken to work out the timing of maximum wind stress and storminess. c, d –  Examples of Traumatic Resin Ducts in the tree rings.

Once assembled, the decadal variability of the winter time record was clearly related to the Pacific Decadal Oscillation (see below). This new record is the first of its kind and gives us a new record of wintertime variability from the North Pacific.

Rob Wilson (University of St. Andrews) lead a study from the Yukon. He used blue intensity tree-ring records from white spruce to improve dendroclimatic temperature reconstructions from the southern Yukon.

The study is titled: Improved dendroclimatic calibration using blue intensity in the southern Yukon. and the abstract reads like this: In north-western North America, the so-called divergence problem (DP) is expressed in tree ring width (RW) as an unstable temperature signal in recent decades. Maximum latewood density (MXD), from the same region, shows minimal evidence of DP. While MXD is a superior proxy for summer temperatures, there are very few long MXD records from North America. Latewood blue intensity (LWB) measures similar wood properties as MXD, expresses a similar climate response, is much cheaper to generate and thereby could provide the means to profoundly expand the extant network of temperature sensitive tree-ring (TR) chronologies in North America. In this study, LWB is measured from 17 white spruce sites (Picea glauca) in south-western Yukon to test whether LWB is immune to the temporal calibration instabilities observed in RW. A number of detrending methodologies are examined. The strongest calibration results for both RW and LWB are consistently returned using age-dependent spline (ADS) detrending within the signal-free (SF) framework. RW data calibrate best with June–July maximum temperatures (Tmax), explaining up to 28% variance, but all models fail validation and residual analysis. In comparison, LWB calibrates strongly (explaining 43–51% of May–August Tmax) and validates well. The reconstruction extends to 1337 CE, but uncertainties increase substantially before the early 17th century because of low replication. RW-, MXD- and LWB-based summer temperature reconstructions from the Gulf of Alaska, the Wrangell Mountains and Northern Alaska display good agreement at multi-decadal and higher frequencies, but the Yukon LWB reconstruction appears potentially limited in its expression of centennial-scale variation. While LWB improves dendroclimatic calibration, future work must focus on suitably preserved sub-fossil material to increase replication prior to 1650 CE.

The Figure above shows the location of the Yukon study site and includes various other sites the Wooster lab has worked on in Alaska. Rob has been a great help in the efforts at the Wooster Tree Ring Lab facilitating our lab’s ability to perform these analyses.

Mary Garvin (Biology, Oberlin College) lead the study using tree-rings and chemical analyses entitled: A survey of trace metal burdens in increment cores from eastern cottonwood (Populus deltoides) across a childhood cancer cluster, Sandusky County, OH, USA.  

Abstract: A dendrochemical study of cottonwood trees (Populus deltoides) was conducted across a childhood cancer cluster in eastern Sandusky County (Ohio, USA). The justification for this study was that no satisfactory explanation has yet been put forward, despite extensive local surveys of aerosols, groundwater, and soil. Concentrations of eight trace metals were measured by ICP-MS in microwave-digested 5-year sections of increment cores, collected during 2012 and 2013. To determine whether the onset of the first cancer cases could be connected to an emergence of any of these contaminants, cores spanning the period 1970–2009 were taken from 51 trees of similar age, inside the cluster and in a control area to the west. The abundance of metals in cottonwood tree annual rings served as a proxy for their long-term, low-level accumulation from the same sources whereby exposure of the children may have occurred. A spatial analysis of cumulative metal burdens (lifetime accumulation in the tree) was performed to search for significant ‘hotspots’, employing a scan statistic with a mask of variable radius and center. For Cd, Cr, and Ni, circular hotspots were found that nearly coincide with the cancer cluster and are similar in size. No hotspots were found for Co, Cu, and Pb, while As and V were largely below method detection limits. Whereas our results do not implicate exposure to metals as a causative factor, we conclude that, after 1970, cottonwood trees have accumulated more Cd, Cr, and Ni, inside the childhood cancer cluster than elsewhere in Sandusky County.

Figure that shows the extent of the cancer cluster that coincides with more accumulated Cd, Cr and Ni in the tree-rings.

Tree Corpsvisits the Wooster Tree Ring Lab. Tree Corps is a program run out of the Holden Arboretum designed to provide training to the arboriculture workforce in the Cleveland Area. It is funded by the Cleveland Foundation and this is the second year the group has visited Wooster. We all learned a lot from each other and everyone got to core some of the oaks on campus with the end of assessing tree health and age.

The group discusses the information that can be derived from the tree-ring record. This black oak shows outward signs of deterioration, however inside it is solid. In terms of management, the location of the tree with respect to foot traffic,  balanced with other pressing tree issues across campus, all need to be considered when assessing the possible removal of this tree.

Nick extracts a core from the oak and discusses the reasons for the various discolorations of the wood.

Josh Charlton (class of 2019, purple shirt) was visiting the lab and offers some advice in coring – thanks Josh for your help.

We also spent some time coring pin oaks on campus. Great fast growing trees – the group mounted up the cores and analysis of the tree rings is underway. Thanks to Tree Corps for making it down to the lab, we look forward to following the future progress of the group in arboriculture.