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1 Testing the Feasibility of Dendrogeomorphic Studies in the Southeastern U.S. on Mt. Le Conte, Great Smoky Mountains National Park, Tennessee, U.S.A. Maegen L. Rochner* Laboratory of Tree-Ring Science Department of Geography University of Tennessee Knoxville, Tennessee 37996-0925 E-mail: [email protected] Henri D. Grissino-Mayer Laboratory of Tree-Ring Science Department of Geography University of Tennessee Knoxville, Tennessee 37996-0925 *Corresponding Author e Geographical Bulletin 57: 1-13 ©2016 by Gamma eta Upsilon ABSTRACT Dendrogeomorphic analyses of mass movement events have been sparingly con- ducted at sites in the western United States, and are especially uncommon in the eastern U.S. e goal of this study was to determine if southeastern tree species in Great Smoky Mountains National Park (GSMNP) record evidence of debris slides in their tree-ring record. Following initial reconnaissance on three debris slide scars on Mt. Le Conte in GSMNP, we performed preliminary den- drogeomorphic analysis on one of the slides, LC01. is slide is considered, although not thoroughly documented, to have oc- curred following a cloudburst on September 1, 1951. e identification of suppressed growth beginning in 1952 confirmed the cor- respondence of the debris slide at LC01 with the cloudburst event and, combined with the identification of accessible and discernable evidence of the impact of debris slides on trees, served as confirmation of current and future use of dendrogeomorphic methods on Mt. Le Conte and in GSMNP. Key Words: dendrogeomorphology, tree rings, Mt. Le Conte, Southeast US, Great Smoky Mountains National Park INTRODUCTION Shroder (1978) outlined the impacts of mass movement events on trees and their subsequent responses. He described the Process-Event-Response approach for un- derstanding relationships between landscape- modifying processes that lead to specific types of mass movement events that leave anatomical evidence in tree boles and the tree-ring record. e “event” describes what happens to the tree as a consequence of the geomorphic occurrence, such as tree tilting, corrosion, burial, exposure, inundation, and nudation. e “response” describes the bio- logical response of the tree to the event, such as scarring, growth suppression or release,

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Testing the Feasibility of Dendrogeomorphic Studies in the Southeastern U.S. on Mt. Le Conte, Great Smoky Mountains National Park, Tennessee, U.S.A.Maegen L. Rochner*Laboratory of Tree-Ring ScienceDepartment of GeographyUniversity of TennesseeKnoxville, Tennessee 37996-0925E-mail: [email protected]

Henri D. Grissino-Mayer Laboratory of Tree-Ring ScienceDepartment of GeographyUniversity of TennesseeKnoxville, Tennessee 37996-0925

*Corresponding Author

The Geographical Bulletin 57: 1-13©2016 by Gamma Theta Upsilon

ABSTRACT

Dendrogeomorphic analyses of mass movement events have been sparingly con-ducted at sites in the western United States, and are especially uncommon in the eastern U.S. The goal of this study was to determine if southeastern tree species in Great Smoky Mountains National Park (GSMNP) record evidence of debris slides in their tree-ring record. Following initial reconnaissance on three debris slide scars on Mt. Le Conte in GSMNP, we performed preliminary den-drogeomorphic analysis on one of the slides, LC01. This slide is considered, although not thoroughly documented, to have oc-curred following a cloudburst on September 1, 1951. The identification of suppressed growth beginning in 1952 confirmed the cor-respondence of the debris slide at LC01 with the cloudburst event and, combined with the identification of accessible and discernable evidence of the impact of debris slides on trees, served as confirmation of current and future use of dendrogeomorphic methods on Mt. Le Conte and in GSMNP.

Key Words: dendrogeomorphology, tree rings, Mt. Le Conte, Southeast US, Great Smoky Mountains National Park

INTRODUCTION

Shroder (1978) outlined the impacts of mass movement events on trees and their subsequent responses. He described the Process-Event-Response approach for un-derstanding relationships between landscape-modifying processes that lead to specific types of mass movement events that leave anatomical evidence in tree boles and the tree-ring record. The “event” describes what happens to the tree as a consequence of the geomorphic occurrence, such as tree tilting, corrosion, burial, exposure, inundation, and nudation. The “response” describes the bio-logical response of the tree to the event, such as scarring, growth suppression or release,

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Maegen L. Rochner and Henri D. Grissino-Mayer

tree death, basal sprouting, and formation of reaction wood. Secondary succession can also occur when trees reestablish on exposed slopes and deposits. Tree-ring evidence, ob-served as the “responses” listed above, can then be used to determine when the “events” occurred (Shroder 1978). The use of tree-ring evidence to analyze geomorphic events, such as debris slides, is known as dendrogeomor-phology.

The term “debris slide” is defined by Easterbrook (1999) as the “rapid downward movement of predominantly unconsolidated and incoherent debris in which the mass does not show backward rotation but slides or rolls forward, forming an irregular hummocky deposit.” Debris slides are most common in mountainous areas where thin layers of sediment collect on top of bedrock layers that dip in the same direction as the slope. Heavy rainfall often leads to saturation of these thin layers, which can break loose as masses of unconsolidated sediment and rock and slide over the top of the tilted planar bedrock surfaces (Easterbrook 1999). Debris slides are a common natural disturbance on Mt. Le Conte in Great Smoky Mountains National Park (GSMNP), where thin soil layers under-lain by tilted Anakeesta Formation bedrock are prone to sliding after heavy rainfall events (Hadley and Goldsmith 1963; Moore 1988; Henderson 1997). We chose Mt. Le Conte for our study because of the high number of visible debris slide scars and efficient access to these scars from trails, roads, and drain-age systems. Henderson (1997) performed an initial dendrogeomorphic analysis of debris slide susceptibility in the Mt. Le Conte-Newfound Gap area of GSMNP, but his focus was on secondary succession, using the establishment dates of trees to estimate the minimum dates of debris slides.

Despite high incidence of mass movement events in the Appalachian Mountains of the eastern United States, dendrogeomorphology has been used rarely in the region, especially in the southeastern United States and in GSMNP. Possible reasons for the scarcity of dendrogeomorphic studies, identified during

our own attempts to perform dendrogeomor-phic analyses in GSMNP, are accessibility and terrain. Accessibility was a determining factor when we chose our study sites on Mt. Le Conte, as vegetation in GSMNP, espe-cially at lower elevations in summer, grows rapidly, and thick underbrush sometimes restricted access to slide scars and perimeter trees and made it difficult to identify trees for sampling. In the case of lower elevation slide scars, the rapid growth of vegetation made it challenging to even locate the slide scars. The three slides investigated for this study were primarily accessible via the slide scars themselves, which bisected trails, roads, and streams in the park. Because such research can require off-trail hiking and impacts to vegetation, finding access points while leav-ing minimal impact on the environment will be especially difficult in future studies of the slide scars in GSMNP. Where steep slopes and loose talus also occur, appropriate climb-ing gear and other safety equipment will be necessary to access and sample on some de-bris slide scars in the park. These two factors, vegetation and terrain, are limiting factors that preclude extensive dendrogeomorphic studies in GSMNP and are possible reasons for the deficiency of such work in the park.

Despite these limitations, debris slides still pose a threat to human life and prop-erty in GSMNP. Dendrogeomorphology can be used to not only determine the dates of these events in the park, but can also be used to identify debris slides and flows no longer visually evident or not reported in historical records. The addition of these events to the record can contribute to mass movement inventories and the improved identification of high-risk areas (Stoffel and Bollschweiler 2008). Because of the lack of dendrogeo-morphic studies in the eastern United States and in GSMNP, we first sought confirma-tion of the ability of trees to record a debris slide signal before we performed a complete dendrogeomorphic analysis. A preliminary exploration of the visible impacts of debris slides on trees in GSMNP was needed to better understand the external evidence

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needed when identifying which trees are most likely to have recorded debris slide events in their rings. In other words, we first sought to identify the “events” described by Schroder (1978): tree tilting, corrosion, burial, exposure, inundation, and nudation. The first goal of this study, therefore, was to perform reconnaissance on identified debris slide scars on Mt. Le Conte, recording any tilted, scarred, or buried trees, as well as any trees with exposed roots or other apparent damage. We also identified areas where land was cleared by a slide (nudation), with or without evidence of tree regeneration or secondary succession, and searched for areas where debris had collected in debris dams or debris balls (piles of debris most often at the base of a slide), as these areas contain trees killed by the slide.

The second goal of this study was to perform a preliminary dendrogeomorphic analysis on one slide using a documented debris slide event date of September 1, 1951 (Bogucki 1970) on Mt. Le Conte. Our primary objec-tive was to determine if dendrogeomorphic study is feasible in GSMNP. If supported by the results of this study, the validation of dendrogeomorphic methods in GSMNP will open doors for future similar work in the park and perhaps in other comparable sites throughout the southeastern United States. The application of dendrogeomorphology in these areas will provide the data needed to complete mass movement inventories and identify areas most susceptible to slope failure in the future.

STUDY SITES

We investigated three debris slide scars on Mt. Le Conte (Fig. 1) in GSMNP for visual evidence of the impact of a debris slide on trees: LC01 (an undated debris slide) at N 35.65100 W 83.44100, approximately 1850 m elevation at highest point; SB-8 (a 1951 cloudburst slide studied by Bogucki 1970) at N 35.65147 W 83.43591, approximately 1880 m elevation at highest point; and LC02 (a recent slide from approximately August

2012) at N 35.63928 W 83.44772, approxi-mately 1550 m elevation at highest point. We chose one of these sites, LC01, as the focus of our preliminary dendrogeomorphic analysis based on the abundance of easily accessible, slide-perimeter trees at the site.

LC01 is a debris slide complex that con-sists of three slide areas joined at the base and bisects the Alum Cave Bluffs Trail in GSMNP about 6.5 km from the trailhead at Highway 441. The slide scar drains into the Trout Branch in GSMNP. LC01 is the shortest of the three slides investigated, with a length of 0.2 km long from the highest point to where it becomes less prominent in a narrow drainage. LC01 lies on the rust-stained Anakeesta Formation, which includes metasiltstone, phyllite, slate, metasandstone, schist, and dolomite (Hadley and Goldsmith 1963). The steep dip of this formation leads to thin soil layers and frequent debris and landslides in GSMNP (Hadley and Gold-smith 1963; Moore 1988; Henderson 1997). Because of the high elevation at LC01, red spruce (Picea rubens Sarg.) and Fraser fir (Ab-ies fraseri (Pursh) Poir) are the dominant tree species along the edges of the slide scar.

Like SB-8, LC01 is believed to have origi-nated during the September 1, 1951 cloud-burst event, but unlike for SB-8, this date has not been fully confirmed in the literature. The cloudburst, however, is known to have triggered multiple debris slides on the south face of Mt. Le Conte (Bogucki 1970, 1976). Bogucki (1970, 1976) focused on slides that occurred in the Styx Branch drainage into Alum Cave Creek, just east over a ridge from the Trout Branch drainage and LC01, but did picture an undated slide (Bogucki 1976) iden-tified as having occurred in the Trout Branch drainage. If this pictured slide did indeed oc-cur during the September 1, 1951 cloudburst, the trees at LC01 should mark the event in the following growing season of 1952.

SB-8 (Bogucki 1970), like LC01, is also at high elevation and is underlain by the Anakeesta Formation. The head of the SB-8 slide scar is located at N 35.652457 W 83.436154, approximately 1880 m el-

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evation, and stretches approximately 0.4 km downslope until in joins the chute of another documented 1951 slide, SB-10 (Bogucki 1970). Both SB-8 and SB-10 drain into the Styx Branch in GSMNP. We accessed this slide from the switchback with stairs on the Alum Cave Bluffs Trail approximately 6 km up from Highway 441 (N 35.650362 W 83.435419). Spruce and fir dominate the perimeters of the slide scar.

The final slide scar we investigated, LC02, lies at a lower elevation, but is the longest and most recent slide of the three studied. Bedrock exposed on LC02 consists of Anakeesta slate and phyllite and Thunderhead sandstone. Estimated to have occurred around August 2012, LC02 is approximately 1.6 km long from head to base where it intersects Trout Branch at N 35.637140 W 83.454513, ap-

proximately 1235 m elevation. The slide head is visible from the Alum Cave Bluffs Trail about 3.6 km up from Highway 441 and lies only about 5 m downslope from the trail. A wide variety of tree species dominate along the perimeter of the slide scar, including yellow birch (Betula alleghaniensis Britton), American beech (Fagus grandifolia Ehrh.), yellow poplar (Liriodendron tulipifera L.), red oak (Quercus rubra L.), white oak (Quercus alba L.), yellow buckeye (Aesculus flava Sol.), sugar maple (Acer saccharum Marsh), and red maple (Acer rubrum L.). At the higher elevations of LC02, red spruce trees are more abundant. We accessed LC02 via the Trout Branch, which is accessible where it flows under Highway 441 in GSMNP at N 35.634512 W 83.461199, at approximately 1132 m elevation. The debris ball of LC02

Maegen L. Rochner and Henri D. Grissino-Mayer

Figure 1. Map of the three investigated slide scars on the south facing slopes of Mt. Le Conte in GSMNP. Slide scars are indicated by the gray shaded, black outlined areas labeled LC01, SB-8, and LC02. Map generated using Google Maps.

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lies about 0.8 km up Trout Branch from the highway. We considered LC02 too recent to be useful for tree-ring science, as the effects on growth would likely still be underway, but did observe LC02 as a rare opportunity to observe the recent effects of a debris slide on trees and consider what evidence is cur-rently being recorded for future study at the site. The LC02 site will eventually provide an opportunity to use dendrogeomorphic methods to confirm or refute the 2012 date, but also to identify any additional slides that may have occurred in the past.

METHODS

Evidence of Debris Slide Occurrence in Trees

We hiked into the area of the three debris slide scars and took photographs of known debris slide “events” (Shroder 1978) in trees bordering and near to (within 5 m) the debris slide scars. We photographed evidence of in-jury, removal of roots, damage to the crown, scarring, tilting, secondary succession, and trees killed by the debris slide both on the perimeter of the slide and preserved within debris or log jams along and at the bottom of the debris slide. The results of this recon-naissance are presented for the purpose of this manuscript as results, but are presented in the context of a review of the process-event-response sequence outlined by Shroder (1978) as a way to organize what we found. Ultimately, the first portion of this study is meant to serve as a summary of the evidence needed to perform a dendrogeomorphic study, illustrated with photographs that con-firm the viability of finding this evidence in GSMNP and possibly in other locations in the southeastern U.S. despite the shortage of dendrogeomorphic research performed there.

Preliminary Dendrogeomorphic Analysis

We collected a preliminary set of cores from 20 red spruce trees based on proxim-

ity to the main slide area at LC01. Trees in GSMNP could not be cut down to obtain cross sections, so sampling was limited to increment cores, which we collected using a Haglof 3-thread increment borer. For the purposes of this pilot study, we chose to fo-cus on the identification of suppression and release sequences within the tree-ring record. A growth suppression sequence is a period of years with visibly reduced growth, as much as a 200% reduction or more (Schweingruber et al. 1990; Carrara and O’Neill 2003; Arbellay et al. 2010; Clague 2010; Saez et al. 2012), following injury, damage to the crown, or the exposure of roots. A growth release sequence is a period of years with increased growth, as much as a 200% increase or more (Schwein-gruber et al. 1990; Carrara and O’Neill 2003; Arbellay et al. 2010; Clague 2010; Saez et al. 2012), following the removal of competition by a debris slide. Trees most likely to have experienced suppression, release, or both are located on or near the perimeter of a debris slide scar. Trees that are on the perimeter but have not been injured may experience growth release. In some cases, a tree can be injured, causing suppressed growth, but after a short period of recovered growth, can experience reduced competition and a growth release (Schweingruber et al. 1990; Carrara and O’Neill 2003; Arbellay et al. 2010; Clague 2010; Saez et al. 2012). Even if trees are me-ters away from the slide scar, they can still show release after removal of nearby com-petition, or suppression following injury or exposure of roots that extended laterally into slide areas. To accommodate this possibility, we sampled trees within five meters of the slide area.

We sanded all cores using progressively finer sandpaper, beginning with ANSI 80-grit (177–210 µm) and finishing with ANSI 400-grit (20.6–23.6 µm) to increase visibility and accuracy when measuring ring widths (Orvis and Grissino-Mayer 2002). Once sanded, we marked tree rings using the standard decadal dot notation, starting at the outermost complete ring and count-ing towards pith (Stokes and Smiley 1996;

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Speer 2010). All samples were taken from living trees so the date of the outermost ring was known. Counting inward from bark, we dated all rings and the year of the innermost complete ring noted for measuring. We measured total ring widths to 0.001 mm ac-curacy, starting with the innermost complete ring, using a Velmex measuring system and MEASURE J2X software.

We internally crossdated all measured series using COFECHA (Holmes 1983; Grissino-Mayer 2001) to properly place each series in the correct temporal alignment with the other series. A correlation threshold of 0.40 is used in the Southeastern US (International Tree-Ring Data Bank (ITDRB) 2016a) to en-sure correct crossdating. Segments analyzed were 40 years in length lagged by 20 years, and the critical correlation for segments was 0.37 (Grissino-Mayer 2001). Internal cross-dating is necessary to determine the date of the final ring and to identify missing rings. We used the presence of latewood-earlywood to determine the last possible complete ring because trees were sampled during and after the 2013 growing season. We developed the final raw chronology for the LC01 site using the program WIN-ARSTAN (Cook 1985). To evaluate the feasibility of dendrogeo-morphic study in GSMNP, we used the September 1, 1951 cloudburst event as a test and observed both the individual cores and the final raw chronology for evidence of the onset and continuation of suppressed and/or released growth beginning in the following growing season of 1952.

RESULTS

Evidence of Debris Slide Occurrence in Trees

We identified all of the “events” outlined by Shroder (1978) during our exploration of the three debris slide scars on Mt. Le Conte in GSMNP. Visible scars were rare, but we identified one recent scar on a birch tree from LC02 (Fig. 2) and what appeared to be an older scar on a red spruce tree from

LC01, which we sampled for further analysis (Fig. 3). Scars are often used in dendrogeo-morphology because, just as fire scars in the tree-ring record can indicate the year of a fire (Grissino-Mayer 1995), scars due to injury from falling or sliding debris can be dated to

Maegen L. Rochner and Henri D. Grissino-Mayer

Figure 2. Injured and scarred yellow birch tree adjacent to LC02 whose bark was re-moved by a debris slide (Photo by Maegen Rochner).

Figure 3. Co-author Dr. Henri Grissino-Mayer collects a core adjacent to a scar in a red spruce tree at LC01 (Photo by Maegen Rochner).

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determine an event year. In some cases, scars from a past debris slide are still visible, such as seen in the examples above, but in many cases, trees have already grown over older scars, which makes them hidden, or buried, within the tree and much harder to find.

For the scarred red spruce on LC01, we sampled according to Stoffel and Bollschwei-ler (2008), and collected cores from within, opposite of, and adjacent to the scar. The core taken adjacent to the scar must be close enough to obtain evidence of the callus tis-sue and perhaps traumatic resin duct (TRD) formation (Stoffel and Bollschweiler 2008). In conifers, TRDs are often formed as a re-sponse to some injury and are seen in tree rings as a row of vessel-like features (bisected ducts) that transport resin down a tree to the wounded area. These can be dated to the exact year the injury occurred (Stoffel 2006;

Stoffel and Bollschweiler 2008; Saez et al. 2012). We did not observe any TRDs in our red spruce samples from LC01. The scarred tree on LC01 proved to be approximately six to seven years old and did not support a 1951 debris slide date at the site.

To locate trees most likely to have expe-rienced growth suppression or release, we focused primarily on trees located on the perimeter of the surveyed slide scars (Fig. 4). However, we also identified an example of the lateral extension of roots into a slide area (Fig. 5), which supported the five meter buf-fer that we applied to our sampling methods at LC01. We identified one example on LC02 (Fig. 6) that experienced both injury and the removal of roots, as well as debris damming against its base and tilting. Debris sliding downslope can act as a bulldozer, displacing trees or tilting them in the direction of flow. Tilting is most common at the base of a slide, at the debris ball, such as seen at LC02 (Fig. 7), but can also form where debris is jammed up against the trunk of a tree in a debris dam (Fig. 6). Trees that survive tilting return to a more upright position by forming reaction wood: compression wood on the downhill side of gymnosperms (conifers) and tension wood on the uphill side of angiosperms (hardwoods) (Stoffel and Bollschweiler 2008). Reaction wood generally appears as wider, darker rings on the reacting side of the

Testing the Feasibility of Dendrogeomorphic Studies in the Southeastern U.S. on Mt. Le Conte

Figure 4. Debris slide scar at LC02. Trees on the perimeter of the slide scar may record the event in their rings because they are near enough to have been affected by the slide or to have experienced a decrease in competition (Photo by Maegen Rochner).

Figure 5. Red spruce at LC01 with roots, indicated by black arrows, extending laterally into the main slide scar (Photo by Maegen Rochner).

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trunk (uphill or downhill) and consequently, narrower, sometimes absent rings on the op-posite side. In most cases, the beginning of reaction wood growth occurs close to the tilting year, but in some, it can be delayed by a recovery period characterized by nar-row ring growth (Carrara and O’Neill 2003). During our preliminary study on LC01, we did not identify any trees tilted by debris. In addition, the steep slopes at LC01 made it difficult to differentiate between trees that were tilted by the debris slide event and trees that were tilted by soil creep.

In addition to mature red spruce trees on the perimeter of the slide (with evidence of suppression or release, scarring, or tilting), younger trees that represent regeneration on old slide scars are also useful in a den-drogeomorphic study. Regeneration of new vegetation occurs as a response to the removal of surface material, as land stripped clean by mass movement events allows growth of new forest where soil material has collected on

exposed surfaces. The establishment dates of trees on previously exposed slopes may provide estimates of minimum event ages, but regeneration rates can vary depending on microclimate and habitat factors, creating a lag time between the mass movement event and plant establishment (Shroder 1980; Hupp et al. 1987; Stoffel and Bollschweiler 2008, 2009; Clague 2010).

On the higher elevations of Mt. Le Conte, climate and geologic conditions slow the re-establishment of Fraser fir and red spruce (Flaccus 1959; Pauley 1993; Wise and Pe-tersen 1998). The exposure of bedrock ini-tially favors light-tolerant and fast-growing mosses and grasses (Crozier 1984; Ryan 1989), but the establishment of other species, especially trees, is a much slower process. A shorter growing season, combined with steep slopes, harsh climate, and acidic soils, make the regeneration process slow on Mt. Le Conte (Schneider 1973; Ryan 1989; Wise and Petersen 1998). At high elevation sites of disturbance, bare rock and talus slopes can remain bare for up to 100 years and trees are the slowest to recover through secondary suc-cession (Flaccus 1959). Exposed bedrock and continued headward erosion make it harder for red spruce to establish on the steep slopes of the slide head, especially when red spruce reproduction tends to occur in pulses (Pauley 1993). Successful red spruce regeneration is more likely when favorable soil levels and

Maegen L. Rochner and Henri D. Grissino-Mayer

Figure 6. Red spruce on the perimeter of slide LC02 with exposed roots and injury, includ-ing a debris dam pushed against it (Photo by Maegen Rochner).

Figure 7. Trees tilted and killed by debris damming near the base of LC02 (Photo by Maegen Rochner).

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conditions coincide with a reproductive pulse (Feldkamp 1984; Pauley 1993). The combination of harsh conditions and proper timing has slowed the re-establishment of red spruce at LC01. In addition, LC01 (1800 m) is located near the fir line at 1900 m (Whit-taker 1956), and Fraser fir is likely hardier at this elevation and the first to re-establish on exposed slopes. On the debris slide scar of LC01, we found that Fraser firs have been the first to regenerate (Fig. 8) and did not observe any spruce seedlings or saplings at the site.

Trees killed by a debris slide, either by re-moval or by injury, can also provide evidence of the date of a debris slide. Accessible logs in dams or jams, such as seen on SB-8 (Fig. 9), were abundant on all three studied slides. The death dates of these trees will be equal to the date of the debris slide unless a lag time exists between injury and death. Preserved logs found in a slide debris ball, like that seen at LC02 (Fig. 10) or in debris dams, can provide death dates as long as they remain well-pre-served and their outer rings are intact. How-ever, the chronologies provided by such trees are floating in time, and must be crossdated with other living chronologies to determine outer ring dates. To use the age defined by the rings of the tree to date the event requires the assumption that the landslide killed the tree within the final growth year. If bark is pre-served, this assumption holds better than with other pieces of debris because woody debris

on the forest floor that could be derived from long-dead material could have been carried by the slide. Because of such complications, den-drochronology works best if multiple methods are applied when dating debris flows or other mass movements (Clague 2010).

Preliminary Dendrogeomorphic Analysis

The final raw LC01 chronology (Fig. 11) covered the period 1815–2013 and consisted of 20 dated tree-ring series from 20 individu-al red spruce trees. The mean segment length was 150.6 years. The interseries correlation was 0.46 (p ≤ 0.0001), which is above the critical threshold of 0.40 for southeastern trees (ITRDB 2016a) but below the average (0.56) for red spruce (ITRDB 2016b). The mean sensitivity was 0.21, slightly below the average (0.22) for red spruce (ITRDB 2016b). Mean sensitivity measures changes in

Testing the Feasibility of Dendrogeomorphic Studies in the Southeastern U.S. on Mt. Le Conte

Figure 8. Fraser fir regeneration on the slide scar head above Alum Cave Bluffs trail at LC01 (Photo by Maegen Rochner).

Figure 9. Pile of plant debris in the slide scar of SB-8. The death dates of downed trees can help provide approximate dates of the debris slide (Photo by Maegen Rochner).

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Maegen L. Rochner and Henri D. Grissino-Mayer

year to year ring width, with high values indi-cating higher sensitivity to climate variables. Values vary from high for drought-sensitive conifers (0.65) to low for complacent trees (0.15) that experience few limiting factors in favorable environments (ITRDB 2016b). In the southeastern U.S., a minimum mean sensitivity of 0.20 is typically required to indicate the climate sensitivity needed for crossdating.

Visual analysis of the 20 LC01 cores and the final LC01 chronology indicated an event that led to suppressed growth beginning in the growing season of 1952. Seven of the 20 sampled trees exhibited a growth suppres-sion beginning in the year 1952 (Fig. 12) (LC01-01, LC01-02, LC01-05, LC01-07, LC01-08, LC01-17, and LC01-19), one tree beginning in 1954 (LC01-18), and one tree beginning in 1955 (LC01-06). A graph of the LC01 chronology also shows a sudden and sustained decrease in growth in 1952 (Fig. 11). The 1952 suppression immediately fol-lowed a wide ring in 1951, and was sustained until a minor recovery in growth in 1960.

Figure 10. Debris ball at the base of LC02 with author, Maegen Rochner, for scale (Photo by Chris Rochner).

Figure 11. The final LC01 chronology (average ring width) covered the period 1815–2013 and consisted of 20 dated tree-ring series from 20 individual red spruce trees. A period of suppressed growth beginning in 1952, which followed a wide ring in 1951, continued until a minor recovery in 1960. The average ring width (indicated by horizontal black lines) during the period 1815 to 1951 was 1.36 mm but, following a shift after the suppression in 1952, was reduced to 0.86 mm for the period 1952–2013.

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Testing the Feasibility of Dendrogeomorphic Studies in the Southeastern U.S. on Mt. Le Conte

The graph also shows a shift in average ring width following the 1952 suppression, as the average ring width does not recover to that of the previous period 1815–1951 (1.36 mm) in the post-suppression period 1952–2013 (0.86 mm) (Fig. 11).

CONCLUSIONS

Based on the identification of accessible and discernable external evidence of the im-pacts of debris slides on trees in GSMNP and the discovery of internal evidence support-ing the correspondence of suppressed growth and a known slide-generating event, the September 1, 1951 cloudburst, at LC01, we conclude that dendrogeomorphology, despite the limitations discussed in this report, is fea-sible in GSMNP. During our investigation of the three debris slide scars on Mt. Le Conte, we identified all of the “events” outlined by Shroder (1978). The identification of this evidence will assist with future identification of trees most likely to contain evidence of debris slide events in their rings, thus aiding future dendrogeomorphic study in GSMNP. Preliminary results from dendrogeomorphic

analysis at LC01 also supported continued dendrogeomorphic study in GSMNP. The detection of growth suppression beginning in 1952, the year following a documented debris slide event on Mt. Le Conte, justi-fies the use of dendrogeomorphic methods to detect undocumented debris slides in GSMNP. The likelihood is also high that dendrogeomorphology is a feasible approach for helping answer geomorphic questions in the southeastern U.S. The capacity for tree-ring reconstruction of past debris slide events exists in GSMNP and opens doors for future work in the park and perhaps elsewhere in the Appalachian Mountains and the south-eastern U.S.

ACKNOWLEDGEMENTS

Partial support for this project was pro-vided by a Science Alliance Fellowship from the University of Tennessee-Knoxville Department of Geography. We thank Paul Super, Science Coordinator of the Appala-chian Highlands Science Learning Center at Purchase Knob in Great Smoky Mountains National Park who assisted with coordinating

Figure 12. Close up of core samples taken from trees LC01-01 and LC01-02 highlighting the onset of suppressed growth beginning in 1952 (black arrow). The black dots portray the standard decadal dot notation used to annotate tree cores. Two dots indicates a mid-century ring and one dot indicates a decade ring.

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Maegen L. Rochner and Henri D. Grissino-Mayer

our work in the park. We also thank Uni-versity of Tennessee graduate students Annie Meltzer, Vi Tran, Anna Alsobrook, Lauren Stachowiak, and Julie McKnight, and under-graduate Rebecca Groh, who assisted in the field and in the lab. This work was completed as partial fulfilment of the requirements for an M.S. degree in the Department of Geogra-phy at the University of Tennessee-Knoxville.

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