Summer Research: Oaks, “Tree-athlons,” and Hogs

My name is Callie Oldfield, and I am a summer intern for the Biology Department under Dr. Jon Evans. I worked with the Herbarium last summer, pressing plants and helping with surveys. This summer, along with my little sister Sarah Oldfied as my assistant, I am finishing a research project that I have been involved with for the past year. Perhaps you have heard of or seen the chestnut oak (Quercus prinus) plot that was established 17 years ago. Just up from Dick Cove, there is a one-hectare plot full of brightly colored flags. Each flag and tag corresponds to a single chestnut oak, which has been scrutinized every year since 1997. For every tree over .5 meters, we know whether they have grown, been damaged, or sprouted. We have tracked the diameter at breast height (DBH) for the larger trees. Random and non-random circle plots have been sprinkled throughout, serving as a place to collect data on seed rain and trees smaller than .5 meters.

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SEI students search for individual trees

This summer, I have been taking environmental data for our one-hectare plot such as moisture, light levels, soil depth, and leaf litter depth. We have taken all of this data for spatial analysis in order to answer the question: what does it take for a chestnut oak acorn to become a canopy tree? So far, it appears to be an almost impossible task. On years of seed rain, most of the acorns are eaten by deer, squirrels, and even insects like weevils. The few that do survive are not likely to grow more than .5 meters. If are able to grow, they will not grow enough to reach the canopy. In the last few years, deer browse has also begun to affect our plot, reducing the chances that any tree will make it to the canopy. Chestnut oaks, however, are hardy and resprout a new stem after damage, though they are unlikely to grow back to their original height. As a result, the population is, on average, getting shorter. This story is not uncommon for oaks – as a whole, they are on decline, however, it had been theorized that Chestnut oaks were more suited to the warming temperatures, and could stick it out on their preferred habitat of rocky outcrops. Our research is painting another picture, one of a declining population that will slowly, slowly disappear if there is no canopy recruitment event in the near future.

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This image shows the locations of all of the chestnut oaks in the entire one-hectare plot

I also had the pleasure of taking this year’s Sewanee Environmental Institute Pre-college program to the chestnut oak plot, where they learned about the research and took on the role of researcher. Sarah, my sister, and I came up with the idea of having two groups go through a “Treeathlon” in the plot. The first leg of the race was a search for individual trees in the plots. I gave them a tree ID number, a location, and a tree size to use in their search. Points were awarded for how many trees they found – and searching for these trees can be difficult when there are hundreds in a 5 meter by 5 meter area. The second round involved taking the data we recorded for a tree (Size, sprouts, damage), and acting out the life of the tree from 1997-2013. This is something we often do when a tree is missing an ID number, or when we encounter a particularly interesting individual. The groups did a wonderful job of entertaining us with their antics, and points were awarded for quality and accuracy of the performance. The third round was an estimation competition – we found a large chestnut oak in the plot and each team guessed its diameter at breast height. The two groups measured with their arms, shoes, and clipboards, and then did the calculation from circumference to diameter – both were within a centimeter of the correct answer. The winners flaunted their expertise, and we returned to Spencer to relax and engage in creative art projects.

Another project I have worked on this summer was analyzing data and writing about about a unique mutualism between wild hogs and a species of nutsedge on St. Catherine’s Island. Using data that Dr. Evans and the Island Ecology class took each year from 1997-2009, we have found that wild hogs are rooting up and eating nutsedge patches on the beach swales, which surprisingly benefits the nutsedge. Nutsedge is a clonal plant, and is able to quickly recolonize the area with its remaining tubers because the other vegetative cover which previously competed with it was killed. We investigated whether this behavior is considered farming, due to the repetitive nature of tilling and harvesting the Nutsedge, and determine that this is the first example of a low-energy farming mutualism between a plant and mammal. We plan to submit our manuscript to a journal before the end of July.

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Yellow nutsedge (Cyperus esculentus)

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A dune swale rooted by wild hogs

As the summer comes to a close, I look forward to continuing my work on the chestnut oak project in the fall and writing my Honors thesis about it. I am also excited to see the results of the hard work from Dr. Evans’s other two summer interns, Thomas Walters and Geanina Fripp. Thomas is studying a new species of cane, just discovered in 2006 – little is known about the ecology of Arundinaria appalachiana, but Thomas is researching its growth over time and response to fire disturbance and light gaps. Geanina, who spent her June working in Hati with Dr. McGrath, is creating content for a website on Belize to be used in blended-learning. Complexities of issues such as illegal palm harvest, endangered animal hunting, and gold mining will be explored, and solutions will be raised. Classes from around the world will be able to use the website to generate awareness about these issues.

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About Callie Oldfield

I was a Post-Baccalaureate Fellow for the Sewanee Herbarium from Winter 2015-Summer 2016. I am currently a PhD student studying Plant Biology at the University of Georgia.

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