A wealth of information can be found encoded in the rings of trees. Tree rings tell us of past weather conditions, forest fires and even the dates of solar flares. Dendrochronology, the study of tree rings, reconstructs past events and conditions by examining the traits of the annual growth rings, namely their width. Our group decided it would be interesting to do some dendrochronology here on Western. Our question was, just what are the effects of annual rain fall and average temperatures on the growth on maple trees here on campus? Are there direct correlations between weather and growth? Does greater than average rain tend to stimulate growth or flood the roots? Is heat detrimental or beneficial for growth? Do freezing temperatures have a significant effect? To determine the answers to these questions, we will compare core samples we obtain with weather records over a twenty year time span.
We hypothesize that higher annual rain fall will result in more growth. Years with little rainfall will have minimal increases in tree diameter. Years with fewer days with freezing temperatures and days of extreme heat (above 95? C) will result in the most growth. Warmer-than-average years will get more growth and cooler-than-average years will result in less growth. The most growth, then, will be found during warm, wet years.
This lab will be very informative as to the effects of weather on tree growth. After the completion of the lab, we will able to confidently state the effects of temperature and rain fall on tree growth, regardless if the data supports our hypothesis or not. Also, it will give us and the rest of the class hands-on experience with coring techniques and methods of measuring annual growth, as they will be coring and collecting data in our class lab. Our group is steadily gaining knowledge about the process that forms tree rings and information that can be obtained from them.
Through our extensive research, our group was able to find three labs performed by other college students relating to our topic. Recently, another Miami student performed a similar study comparing the tree growth of white oak trees to the changing climate conditions over the past seventy years. He hypothesized that a lower than normal precipitation and excessively low temperatures would diminish tree growth. Because his lab is very similar to ours, we will use it as an example of both the effective and ineffective approaches to performing the experiment (Seiler). Similarly, a group of students at Penn State University completed a lab centered on core samples. They were attempting to observe how a fire that occurred a few years before affected the trees in their area. The students wanted to see if the rings would show evidence of the fire. To do this, they used the same techniques we will be using to core the trees. For this reason, we will use this lab as a reference on how we will obtain our data on the environmental factors influencing tree growth (Taylor). The third lab we were able to find was performed by a group of New England students that also studied core samples. In their lab, they analyzed the effects that environmental events have on tree growth. This is another source of comparison we can use for our lab. We can analyze their procedure in order to improve ours (Benjamin).
Our group came across an interesting article about a study done on tree rings in Siberia titled, "Long-term Temperature Trends and Tree Growth in the Taymire". In this study, experimenters deduced that in recent years there had been greater trends in tree growth during the warmest seasons. After extensive research, they were able to determine that the trends in tree growth over the past thirty years differed considerably from those of recent years. From this data obtained by the experiment, the researchers were able to conclude that the greater tree growth in recent years can be attributed to global warming. This study is an example of the useful information that can be obtained by studying tree rings (Jacoby, Gordon, et al). "Wood Anatomy", a similar article we discovered on the topic of tree rings, discusses the various characteristics of trees and focuses on the different layers, such as the sapwood and the pith. Another topic in this article dealing with our lab is the use of tree rings to determine the affects of temperature on tree growth. We can use this as a basis for our analysis of the tree rings and the effects of weather on trees over time ("Wood Anatomy").
The last resource our group was able to find is a website devoted to dendrochronology. It is located on the University of Tennessee webpage. We can use this site to help us formulate and analyze data on the core samples. This useful website also gives us links to other web pages on the same topic if we should need any further information. If needed there are experts there we can contact for assistance (Grassino-Mayer, Henri D.).
III. Materials and Methods
We will be using a borer to obtain core samples from a group of maple trees behind Boyd Hall. These trees can be reached taking the service trail that cuts through the woods south of Boyd and taking a left at a pile of asphalt. These trees will be of the same environment. We will take the samples and measure the annual growth. We will obtain weather records for over the past twenty year. The testing should be statistically sound because we are taking samples from trees similar situations which could cause variation in growth. Unfortunately, we do not have enough time and people to take the number of samples needed to be completely statistically correct. We picked maple trees because they are abundant in this area. We are measuring the growth for the past twenty years because the more years we take data from the more accurate the trends we observe will be. We are limited by time for taking any more data than that. The data collected by students will be trustworthy because we will adequately demonstrate and explain coring methods and supervise them in the field. We will also assist them in the field.
The most important material will be the borer. This is how all of our samples will be obtained. We will be using Stat View to create graphs of the data we collect for comparison purposes. We will research weather data from the Internet. We will use this data to determine how the weather has affected the trees in the area we research.
The class will be taking an active role in helping us to collect this data. First, we will demonstrate how to successfully core a tree without causing harm to it. Then each group will be assigned a tree from which they will make their own core sample. Then they will measure the annual growth rings and record their data. The data will be turned into us for processing.
Average Tree Growth Compared to Weather Data
V. Discussion and Conclusion
We were trying to prove our hypothesis that higher than average precipitation are higher than average temperature. After comparing the growth we measured and annual records of precipitation and temperature we could find no correlation. A R2 value describes the percentage of data that corresponds to linear regression. The closer the R2 value is to 100% the stronger the correlation is. Our R2 values were 4.82 * 10-4 and 9.69 * 10-5, very small percentages, showing that there was almost no correlation. By taking a look at our regression plot one can see how little correlation there is. The points are randomly spaced out and the line is almost flat. This is not a good sign. Our histograms show that our data does not fit the predicted curve very well. From this we can tell that our data was not very accurate.
Why did we get such poor results? One answer would be that there is no correlation between weather and tree growth, but this doesn't seem like the most logical explanation. More likely the problems in our method, namely in our core collecting. We had originally planed to use trees of the same size but then determined that this was not feasible when we also wanted the trees to be of the same type and from the same area so we did not. This might have caused error. We may not have drilled straight enough. Going in at an angle, which is easy to do, make some year's growth appear larger than it actually was. One large problem we encountered was that the tree rings were very difficult to read. Many samples were not used for this reason, including those collected by our peers. If we happened to miss one ring because it was too faint, that would have thrown off all of that sample's data. We performed no T-test because it did not seem this would have given us useful information, though we could have tested to find if each sample was representative of the population of trees as a whole.
If we were to perform the experiment again, we would first take many more samples. This might have minimized some of the error. It would have been good to find a way to dye the rings as well in order to see them better. Another type of tree other than maple may have been easier to read. We would have used our original idea of measuring trees of the same diameter. We would also have several people measure each sample several times to minimize measuring errors.
This lab raised several questions for us. If tree growth really isn't dependent on weather, what is it dependent on? If tree growth is dependent on weather, to what degree? What would be the best method to determine this if not coring trees? How would a higher-quality borer have affected our data? Would have collecting samples at another time of year have made the samples easier to read?
We learned that while we did not prove that tree growth is dependent on weather that does not mean that it is not true. Statistical tests proved that our data was not accurate so that caused us to question our methods. We learned how to assemble and use the borer. We have learned what the word dendrochronology means. We learned about regression and what an R2 value tells you. We learned how to extract a borer that's stuck in a tree. Most importantly, we learned about the proper methods for creating and executing a student-generated lab.
Benjamin, Mike. Forests In Cross Section. New England, 1999.
Grassino-Mayer, Henri D. Ultimate Tree-Ring Web Page. www.web.utk.edu/~grissino/.
August 26, 2000.
Jacoby, Gordon, et al. "Long-term Temperature Trends and Tree Growth in the Taymire Region of Northern Siberia." Quarternary Research July 1999: 312-318.
Seiler, Shawn. The Effect of Climate on White Oak Trees in Oxford, Ohio. http://jrscience.wcp.miamioh.edu/courses/climate405-501.html
Taylor, Alan H. Research at the Penn State Tree Ring Lab. www.geog.psu.edu/tree/research.html. Penn State University, 9-7-00.
"Wood Anatomy" Agriculture, Forestry, and Soils: Forestry Biological and Biomedical Science: Plant Science: Plant Anatomy and Morphology. 4 Sept. 2000
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