DENDROGEOMORPHIC ANALYSIS OF DEBRIS SLIDES ON MT. LE CONTE, GREAT SMOKY MOUNTAINS NATIONAL PARK, TENNESSEE, U.S.A

Research conducted during the past 30 years tested the use of tree rings to date mass movement events in the mountain areas of Europe and the western and southwestern United States, but few studies have been performed in the eastern U.S., where debris flows, landslides, and rock falls in the Appalachian Mountains pose a common threat to human life and property. One area of particular interest is Great Smoky Mountains National Park (GSMNP). For this study, I tested mature red spruce (Picea rubens Sarg.) trees located on or near a debris slide boundary on Mt. Le Conte (LC01) in GSMNP, Tennessee, for a disturbance signal indicative of debris slide events at the site. To first determine if climate influences prevailed at the site and might contribute to abnormal growth patterns, I initially tested sampled trees for climate-growth relationships using DendroClim2002 software. Red spruce on LC01 showed multiple significant climate-growth relationships with monthly and seasonal mean temperature, total precipitation, and PDSI variables. Next, I analyzed suppression and release sequences using a combination of visual and graphical inspection with JOLTS disturbance-detecting software. Detected onset dates identified growth disturbances, but knowledge of significant climate responses in tree growth prompted the use of an ensemble strategy to minimize the influence of the climate signal. I created a difference chronology for analysis in OUTBREAK, compared this with local reference chronologies and with local climate data, and modelled climate using regression residuals in Excel. Combined visual and statistical results provided a list of 20 possible debris slide dates but only three were further supported from results in the ensemble methods: 1909, 1951, and 1981. Results highlighted the importance of the use of an ensemble strategy to better isolate debris slide signals from abnormal growth patterns caused by climate. In the case of LC01, and perhaps GSMNP, both climate and debris slide signals were present in the tree-ring record, and disturbance detection alone was not adequate for identifying debris slide event years. Climate-growth analysis and subsequent removal of climate signals using a control chronology or other methods should always be an initial step in dendrogeomorphic studies.