Mid-Summer Update

This post will be an update from my first post about this summer’s research. Thus far, we have been able to collect tree ring cores and the information about the trees from the TRAYLS group. We have created the Google Earth interactive site that houses this information and is accessible to anyone. We have also added other tree information from Lauren Oakes’s study site and Pleasant Island. We are working on adding data points from Ben Gaglioti’s study site at La Perouse Glacier.

The cores arrived in the mail and were mounted and sanded. The samples came from mountain hemlock and Sitka spruce trees. We were able to create graphs from the data and do some comparing between tree species.

Graph 1. Representing the ring width indices. The black line represents samples so the higher it goes, the more samples overlap during that time. The year 1808 is marked in the graph because of its volcanic events and cooling (Cameron et al., 2006). Although the location of the eruption is unknown, ice cores indicate an eruption occurring from certain chemicals found inside the ice.

In graph 1, the blue line rises to its highest peak around 1880. This means that the rings indices is at the highest point. The tree rings would be thickest indicating the most growth would be happening during this time in all of the overlapping samples.

Graph 2. Representing the ring width indices. Again, the black line represents samples so the higher it goes, the more samples overlap during that time.

In graph 2, the blue line rises to its highest point at about 1900. After this, the line takes a nosedive and drops continuously till 2000. From both graphs, we can speculate what the past environments could have been like. This work is important because it has rarely been studied before. This work can be added to the known information about Alaskan Trees and the history of the area.

Figure 1. An image of the reaction wood in a mountain hemlock sample. Reaction wood means that there was stress imposed on the tree. The darker wood grows to help recover from the stress. Some examples of stress could be wind, weather, or even a bear stepping on a tree as its growing (see below). The tree compensates for the lean in its main stem by putting on denser reaction wood.
Figure 2. Here is an image showing some examples of what the tree and tree cookie would look if the tree has reaction wood.
Figure 3. Showing the two species of samples compared to one another. The Sitka spruce has wider rings and the Mountain Hemlock has thinner rings. Resin ducts (arrows) are seen in the Spruce.

Basics Dendrochronology and Cedar

Each year, a tree grows a ring and this ring can tell us about the climate, growth, and factors influencing the tree that year. The thickness of a ring can tell us the environmental conditions like whether there had been a flood or drought. To study trees, we can take cores with coring tools. This does not harm or kill the tree. We can then analyze the three -rings in each core using principles of dendrochronology.

One principle of dendrochronology is the principle of cross-dating. Because tree rings give us calendar years, we can match previously recorded ring series with new samples to get the years when the tree was living. It’s as if the rings are barcodes; we can match up the lines (rings) to develop and extend a ring-width timeline (see Figure 1 below).

Figure 1. Here is a diagram to help explain the principle of cross-dating (Kumar, 2015).

Another principle of tree-ring analysis is the principle of limiting factors. Limiting factors are environmental factors that can limit the growth of trees. Some examples include temperature, precipitation, sunlight, and nutrients. If a tree experiences a drought, this will be shown in the relative width of the tree rings.

The principle of ecological amplitude suggests that samples should be collected from trees along the edges of environments since those are the most sensitive. These trees will have the best indicators of the past and the climate it went through within its record. For example, one can compare the rings between high elevation and lower elevation trees.

There are many other principles that are applied when studying tree cores, but for the purpose of this blog post and the work done with the TRAYLS group, we wanted to keep the information basic and applied as they cored trees at low and high elevations on Chicagof Island near Hoonah, Alaska.

The TRAYLS group has started coring trees and given us their written data thus far. Julia, one of my classmates and partners in this summer work, created a Google Earth interactive map that has plotted the trees. You can interact with the Google Earth link below.

https://earth.google.com/earth/rpc/cc/drive?state=%7B%22ids%22%3A%5B%221DDEQMmzIAs3FC1mTZ7Es31Szvv3Dz7uh%22%5D%2C%22action%22%3A%22open%22%2C%22userId%22%3A%22105904000101798978065%22%7D&usp=sharing

Alaska Cedar

Today, we are seeing a decline in cedar population in Alaska due to climate change (Hennon, 2016). This is a problem because yellow cedar contributes to Alaska’s economy and has high value in native culture. Yellow cedar is used for strong materials such as paddles, baskets, mats, and many more items. For native culture, cedar is used for totem poles, chests, dishes, and tool handles. Cedar is also important for wood carving. To get the material, the cedar trees are stripped, and the striped bark is soaked. The stripping process is an art and a tradition for native peoples including the Tlingit (Hennon, 2016).

Here is a picture of a stripped cedar tree. After stripping the outer bark, the tree will release meaning that as it continues to grow, the rings will billow out and with the non-stripped bark.
Figure 2. Here is a diagram showing the release while looking down from the top of the tree.

Dr. Ben Gaglioti (University of Alaska – Fairbanks) presented his research to me and other students working under Dr. Wiles in May. The presentation covered cedar basics and information that we could present to the TRAYLS group in our first meeting with them. He also provided the presentation slides to us to use which was a big help in explaining the basics in a visual way. He also discussed the importance of tree ring dating to date glacial advance. Dating when glacier’s advance is just one of the things we can determine using tree cores. Using tree ring dating to determine glacial advance was the focus of my Junior IS that I completed this past spring.

Cedar Decline

Figure 3. Paul Hennon- Here is a map image of the cedar decline in eastern Alaska.

The decline of cedar in response to a changing climate is suggested to be caused from warming temperatures. Because the temperature is rising, the snowpack that forms around the roots and the base of the trees are melting. Snowpacks act as insulators and protect the roots from cold snaps in the winter. The melting snowpack leaves the roots exposed and vulnerable. The warming temperature also influences the timing of dehardening which kills the cedar.

Paul Hennon- The bare, gray trees are dead cedar.

Introduction!

Hi, my name is Claire Cerne and this is my blog for the summer of 2020. I am a student research assistant for Greg Wiles at The College of Wooster. This blog 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, and Dr. Ben Gaglioti and Dr. Dan Mann of the University of Alaska, Fairanks, and several students and I had plans to visit Alaska. I would be going to Dagelet Glacier, on the Gulf of Alaska’s outer coast to collect tree ring. 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 who are interested in studying the forests, terrestrial and marine environment around their town. We would work with the group to add to their lesson plans with presentations and supply them tree-ring data. 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 them and developing them into ring-width series. After this is complete, we will relay the information about the trees they collected cores from. In the meantime, 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.

Here is one of the slides for our first presentation about dendrochronology. This slide shows a cartoon tree core with some basic tree ring principles.
Here is an image of the map Julia made with points from our presentation on the Glacier Bay story. The story is outlined with points showing the locations we discuss in relation to one another.

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.

Here is a picture of me working on my computer at home.

This work has been funded in support by the National Science Foundation. The grant 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.