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NADEF stands for North American Dendroecological Fieldweek. This year the event happened at Pack Forest and I got to be a part of it. What I want to do with the blog is to explain what our group worked on, our results, how a dendrochronology is created, and lots of pictures showing how it is done. Click here for the paper.
Jim Speer, a professor at Indiana State, is the organizer for the entire event. My group had two leaders: Maegan Rochner from the University of Tennessee and Christine Biermann from the University of Washington. The group members were: Trevor Contreras, Beverly Cory, Alessandro Zanazzi, Aaron Snow, Andrew Summers, and Shirley Lorentz. Picture credits go to Beverly, Alessandro, and Trevor. Go below the pictures for more story. Sorry for the sideways pictures - I'll fix that later.
Henri and Maegan preparing tree cores.
Christine, Trevor, and myself dotting cores.
Here I am sanding a core.
At Mt. Rainier with the crew. Skyline Trail.
Aaron and Andrew dotting cores.
Skeleton plots lined up looking for marker years.
A tree core that has been glued in to its base. The tape is so the core won't pop out while the glue is drying. Note that the base has been marked with all data recorded in the notebook.
Alessandro extracting the borer. It is a full-body workout. You must lean back and pull with all your strength.
Shirley measuring the width of the tree rings to 1/100 of a millimeter. This takes a while. There are a lot of rings to measure.
Our planning board - who is doing what and when.
Aaron writing down the years that stand out as low growth years. These low growth years can be used as markers.
Dotting the core. One dot is for 10 years, three dots for a century mark, and two dots for 50 years. Notice how the width of the rings vary.
Maegan marking the base of the core. This is important so you can keep track of all the cores.
Trevor taking GPS coordinates. Notice the notebook in his hand. Each tree and core was recorded.
Raphael with his GPS device looking for a reading.
On the Skyline Trail.
How to do dotting of the tree cores.
Trevor and I removing and packing cores.
The tip of the core is exposed. The tube to carry it is ready. It has already been marked.
Maegan and I working on a core. You had to very careful in removing a core. They can fall apart or break.
Another view of the borer and tree core.
L-R: Trevor, myself, Andrew, Shirley, Alessandro, Beverly, Aaron, Christine, Maegan.
Dendrochronology is based upon the idea that trees will put on one ring of growth every year and that in good years the rings will be fat and in bad years the rings will be narrow. This sequence of fat and narrow rings are seen in most trees in an area. This sequence of fat and narrow rings forms a pattern that can be studied by scientists and used to answer questions.
The measurements of the trees rings are now in a text file and can be processed mathematically with software on a computer. While it is true that the skeleton plots allow for some visual comparisons and crossdating, there is a more accurate way of examining the rings. The first software that was used for processing the data was COFECHA. The program was written by Richard Holmes and the manual for its use was written by Henri Grissino-Mayer. We were lucky to have Henri himself explain how COFECHA works. Overall, COFECHA allows you to double check the accuracy of your tree ring measurements and to average all the samples into one story. Since all the trees are from the same area, they are affected by the same climate. If it is a good year for growth, all of the trees should have a wider than average ring for that year. Now I know what you might be thinking,”What if a rock falls on a tree and that tree had a really rough time during this good year?” This is a true statement - individual trees in individual years will have tree rings that don’t match the average. COFECHA allows to catch these irregularities (or mistakes in measurement).
We took the text files with the measurements and ran those numbers on COFECHA. COFECHA would flag any ring(s) that did not match the average. We then went back to the flagged core sample and re-examined the years in question. Most of the time the problem was simple human error. I made lots of errors. It was very easy to make a mistake. The most common error was to miss a ring. Another issue was traumatic resin ducts (TRDs).TRDs were common and they messed up your measurements.. Trees will respond to injury with TRDs. It is sort of like when we develop a scar on our skin. The TRDs can cover up ring boundaries or entire rings and these can throw off your ring count. If you found the error, measurements were redone and put back in COFECHA . Sometimes there was no explanation why a particular ring did not match the average and there was nothing to fix. Like I said earlier, each tree is an individual and on any given year their growth might not match the average.
At this point in the process we had a set of data that we were confident that it was free of errors. The next piece of software that was used was ARSTAN. It was developed by Dr. Edward R. Cook in 1980. If you plotted the measurements raw, no manipulation, the jumble of spikes and troughs is hard to decipher but ARSTAN removes the “noise” and isolates the effect we want to look at: climate. Here is a link to a NOAA website that gives a more detailed explanation: http://www.ncdc.noaa.gov/paleo/treeinfo.html.
A screen shot of the graphed growth rings, adjusted and raw.
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