The chestnut oak, Quercus montana, lives on dry, nutrient-poor ridge crests of the eastern United States. This oak, which grows on the Cumberland Plateau, has been the subject of a 15 year demography study by Dr. Jon Evans and many of his students over the years. Their central question has been: “What does it take for a chestnut oak seed to become a tree?” and the answer is not as simple as one might think. To perform the study, a one hectare site was divided up into twenty-five 20m x 20m quadrants, and each of the chestnut oaks over a height of .5m was tagged and tracked. Any trees that reached a height of .5m as time progressed were also added to the study. New tree sprouts were counted each year, along with any tree damage, such as top snap or frost damage. The study, which will be the first to focus solely on the chestnut oak and its demography, will be completed this year.
As Dr. Evans, Hali Steinmann (Biodiversity Fellow C’15), and I hiked up to the plot, Dr. Evans remarked that he rarely visited the plot in the summer – the trees are counted each fall because chestnut oaks are the last to lose their leaves. We approached a short chestnut oak, its identification tag wrapped around the trunk. After locating a nearby pink flag which told us the plot number, we were able to look up the tree’s entire history, which had been tracked each year. While it might be under 1m tall, it was once a much taller tree that had suffered frost damage and resprouted. Oaks are known for this interesting growth pattern – the trees resprout if damaged, using the energy supply in their roots. It is possible to count the total number of sprouts a tree had produced by removing the soil from the root collar and counting the stem scars.
Dr. Evans proposed another question about oak resprouting – is it simply a death gasp or do sprouts have the potential to eventually become canopy trees? Tree death can be foretold by sprouting – often a tree will issue several sprouts from its base before the original sprout dies. We found one chestnut oak growing in the place of fallen tree and dug around its base and found that it had resprouted several times. It will take many years to see if that tree makes it into the canopy, and it is possible that it never will. Dr. Evans speculates that the trees that make it into the canopy are not resprouts, but lucky seedlings that were able to take advantage of light availability.
The sprouting mechanism might be a remnant of the time before fire control, in which the tree is poised to regrow after a fire-related disturbance. The data shows that the chestnut oak population is stable, but shrinking in height. “After this study is done, I have to decide whether or not to introduce fire to the site,” he said. Restoring fire to the ecosystem will be an interesting experiment in itself, as it will reveal whether fire is limiting the growth of the oaks, but it would take multiple and repeated burns to achieve the desired ecosystem change. It will also require deer exclusion, since Dr. Evans has shown in other studies that burned areas on the plateau become beacons for deer browse.
While most of the chestnut oak growth is through asexual sprouting of an individual, seeds are released every year. To even become a sapling, these seedlings must fall in specific places. Dr. Evans found that, for a seed to grow, it must land on a concave surface so that leaf cover will protect it. As we walked around a canopy chestnut oak, we saw the numerous rotten and eaten seeds that had not been given a chance to become saplings simply because of where they fell.
As we walked around the plateau, we noticed that blueberries seemed to do well in gap areas, which are areas in which trees have fallen and left a space in the canopy. However, chestnut oaks seemed unaffected by the newly available sunlight. This might be related to a study performed by a Sewanee student which showed that chestnut oaks would not experience rapid upward growth unless they had both high nutrient and high light availability. Another plant that profited from gap dynamics was sassafras , which grows much more quickly than the chestnut oak, experiencing frequent “booms and busts.”
As thunder roared in the distance, we began our walk back down the plateau. We came upon an abrupt change in tree composition – the canopy was now made up of yellow poplar and not oak. Dr. Evans had Hali and I play detective as to why. “Has the soil changed? Is this the product of seed dispersal?” we asked. However, the answer was not natural – the trees had been planted. Dr. Evans showed us how they lined up in rows, reminding us that land use is a very important factor to consider when studying land in the eastern United States. Forest community composition can be dramatically altered as a result of past logging and the creation of plantations. We encountered a white pine plantation as we approached Breakfield Road. “Was this once a field?” Dr. Evans asked. Hali and I looked around; that ditch might have been an old road, we conjectured. But then we saw large rocks littering the ground; Dr. Evans pointed out that rocks were always removed from a field. The area was never a field; the hardwoods were merely cut down and pine planted in their place.
We saw a variety of fascinating insects during the walk, including a Eyed Click Beetle (Alaus oculatus) which landed on me. The flying beetle is a snake mimic; its false eyes and loud snapping motion are attempts to frighten predators. We saw another mimic amongst the oaks which darted around at knee level – a hoverfly. The fly was able to remain perfectly still at one position in the air, flapping its wings so rapidly that they were a blur. While harmless, the fly resembles and sounds like a bee or wasp. We also saw an orchard spider (Leucauge venusta) on a nearby tree, its abdomen large and pill-shaped. Hali recognized the long-jawed orb weaver, having counted it in her spider density studies. As we neared the old Suburban, we saw a different spider hiding in its burrow. Dr. Evans took a blade of grass and moved it about the front of the burrow. The spider pounced, showing off its tarantuloid appearance before disappearing into its den. And with that, we returned to the car, narrowly avoiding the downpour.