Peeking Into the Past, One Ring at a Time

The tree ring lab  – Photo by Tam Tran

By Tam Tran, Climate and Society ’13

Tucked away in the corner of the Lamont campus, a lone building is marked only with the words “Tree Ring Lab” in fading white paint on a cross-section of a tree. Although the lab holds an idyllic charm with dendro-chronologists walking barefoot and sipping foreign teas, this is the home to some of the most ground-breaking tree ring research.

The most common misconception, one of which I was secretly guilty of, is that dendro-chronology consists of primarily counting tree rings. In reality, it is a complex art that requires a great deal of patience, creativity, and more patience. Tree rings are one of a handful of proxies that allow a glimpse into the Earth’s climatic past.

As any child can tell you, a tree makes a ring for each year of growth. In years of good rain, the rings are wide whereas poor rains produce narrow rings. However, the story is far more complicated; trees will also produce missing, false, and micro-rings. It’s a rather insurmountable trade to determine which ring corresponds to what year but if done correctly, a climatic chronology can be built. This requires staring into the microscope for hours and comparing the different width patterns of cores from different trees with one another. Despite the samples being taken from a similar location, the patterns can vary excessively. On top of the whole enchilada, the tropics are notoriously difficult because the irregular ring anomalies make building a chronology even more convoluted.

Tree core sample  – Photo by Tam Tran

Tree ring research could not better illustrate the theme of my Climate and Society master’s program, which acknowledges how climate is inescapably intertwined with society. Brendan Buckley, a forever young New Englander who can be found trekking in the woods or animatedly helping others, has built the first 750 year chronology in Vietnam. Brendan has found that ancient Asian civilizations’ demise often coincide with long droughts. He is now aiming to push the chronology even further back into the medieval period.

Inside the tree ring lab  – Photo by Tam Tram

Based on Brendan’s ambition, I was thrown into the fire with Fokienia hodginsii, a tropical species from Bidoup-Nui Ba National Park in Vietnam, as my first samples to cross-date and have been cheerfully suffering in front of the microscope throughout this summer.  The medieval period contains several notable civilizations, making a longer climate chronology of particular interest to study the relationship between climate and society. My samples have dated as far back as the 1100s and I am currently looking at older cores that date back to the 900s. I often cannot fathom that I am handling millennium-old samples.

One of the questions I constantly asked was, how do you know if you’re right? After determining what years correspond to which ring, each ring width is then measured. Then, thanks to the power of statistics and significance tests (here’s to tipping my hat to my magnificent Quant professor, Tony Barnston, for teaching me information that I can actually apply), the ring measurements from different cores are standardized and compared to see whether the results are significant. As a result, when I’m not squinting and frowning at the microscope, I am punching numbers into the statistical program, Cofecha, and then scowling or cheering at whether or not my cross-dating work is validated. I have spent countless hours staring at a single sample, and trying to decide whether a micrometer difference in a tree ring compared to the next ring can actually correspond to some arbitrary year. Pushing it beyond 1000 AD has proven frustrating to the point of pulling out hairs though because of the lack of samples and the erratic patterns. Yet, I am fueled with exhilaration when I unlock the mystery held by a sliver piece of wood; it is a captivating puzzle, making me often miss my bus. Brendan has opened the doors with his research and I am determined to help pave the road that he has begun.

Work station  – Photo by Tam Tran

My role in this dendrochronology research is a very small part of a larger goal and process. Ultimately, as more is uncovered about the role of climate in a society’s demise or rise, lessons can be gained for our current society. If climate did indeed cause the collapse of seemingly almighty kingdoms, then nature is clearly not a force to be lightly challenged. Yet, in this 22^nd century, I have witnessed history by watching atmospheric CO2 meet the 400 ppm threshold and knowing that it will be many lifetimes, if ever, that annual CO2 maximum falls below that mark. The climate is changing and this MA program has made clear that the negative will likely outweigh the positive. Taking lessons from the past will be crucial to deciphering our future and more importantly, may inspire us to finally take action and seize our destiny.