Spatial and temporal analysis of mass movement using dendrochronology
Abstract
Tree growth and inclination on sloping land is affected by mass movement. Suitable analysis of tree growth and tree form can therefore provide considerable information on mass movement activity.
This paper reports a new, automated method for studying the temporal and spatial aspects of mass movement activity. Ringwidth data from only a few cores per tree are required. The method uses filtering techniques and statistical time series analysis.
Preliminary results for two landslides in the Barcelonnette area of the French Alps show a relative stability of movement activity over the last hundred years (no trend) and short periodicity (six to seven year periods) of mass movement activity.
The advantages of the method (over other, mostly visual, methods) are its clearness, flexibility, repeatability and rapidity. However, further testing is needed to examine its reliability.
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Indicating landslide hazard from tree rings – Ecosystem service provided by an alder forest in the hengduan Mts, Sichuan, China
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Landslide development model based on tree-ring data and quantification of the magnitude of landslide movements
2024, Engineering GeologyAnalysis of landslide events by studying anomalies in tree-ring series of disturbed trees provides unique data on past landslide behaviour. However, a comprehensive spatio-temporal model of landslide evolution using dendrogeomorphic data has not yet been constructed. In terms of determining landslide hazard, one of the key issues, besides the frequency of movements, is their magnitude. Thus, this study is aimed at constructing a model of landslide area development including quantification of landslide displacements. Moreover, not only standard macroscopic growth disturbance but also quantitative anatomical parameters of tree rings were used as a basis for these objectives. The research was carried out on a landslide of the Váh river bank (Slovakia) using data from 32 disturbed black locust (Robinia pseudoacacia L.) individuals. Anatomical analysis revealed a reduction in the vessel lumen area in response to landslide movements. The response was associated with tension wood formation or damage to the tree root system. The reconstructed chronology of landslide movements revealed the main phase of landslide in 2017 and its subsequent evolution. Based on the chronological information and the morphology of the landslide body, a spatio-temporal model of the landslide evolution from the initial slope failure to the present was constructed. The model showed the interrelationships between vertical displacement of the main block, compression and tension deformations within the landslide body, and lateral erosion of the landslide toe by the river. Quantification of the magnitude of landslide displacements was realized from exposed roots in tension cracks but also from the ruptured tree trunk. The limitations and advantages of both approaches are discussed.
Tree-ring analysis is currently a frequently used absolute dating method for spatio-temporal analysis of landslide movements. However, like all absolute dating methods, this approach has various limitations. One possible limiting factor is the inertia of tree growth responses to the influence of landslide movements. When landslide movements occur with a small recurrence interval (months or early years), trees with an inertial response to an older event may not be able to record a younger event. One possible growth response of trees to a landslide movement with the absence of inertia is a change in the size of the vessel lumen area (VLA; anatomical response) in deciduous trees. Thus, this study aimed to quantify the effect of the absence of VLA inertia on the spatio-temporal analysis of two landslide events of known occurrence with a short time between their occurrence (2010 and 2013). Ninety-six individuals of European beech (Fagus sylvatica L.) were sampled and two types of landslide signals (changes in tree-ring eccentricity and changes in VLA size) were extracted from their tree-ring series. The effect of the absence of inertia was evident in the younger event, with 171.2% more trees responding anatomically than through tree-ring eccentricity. In the case of the spatial extent analysis of the younger landslide event, 29.0% more was detected as an active area through anatomical changes (VLA) compared to the tree-ring eccentricity analysis. The use of growth disturbances without inertia could in the future reduce the negative general property of tree-ring-based chronologies of landslide movements, which are considered minimal when using classical growth disturbances with inertia. The implementation of anatomical responses could lead to a more effective use of dendrogeomorphic data in landslide hazard assessment.
Tree-ring eccentricity-based dating of landslide movements: Defining a new effective approach
2024, CatenaDendrogeomorphic dating of landslide movements is nowadays a frequently used tool for understanding past landslide behaviour. One of the most widespread growth disturbances induced by landslides is tree-ring eccentricity. However, extracting the landslide signal from the time series of its values is a challenge that has suffered from many shortcomings so far. In this study, a new approach based on the detection of changes in tree-ring eccentricity values was developed. The approach, which combines the advantages of previous approaches, was tested on four landslides in different physical-geographical conditions with different tree species of different ages. For all landslides, the year of activity was well known and analyses of the results focused on this year. The tested methodological approach successfully detected all these known years. However, it also detected a higher amount of noise in two cases, which may have been caused by imperfect knowledge of pre-landslide slope activity or creep. An important feature identified in the results obtained by the approach was their potential independence of tree age. As with the use of other macroscopic growth disturbances, this approach does not allow dating with seasonal accuracy. However, compared to previous methodological approaches working with tree-ring eccentricity analysis, the new approach demonstrated significant advantages. The procedure does not truncate the reconstructed time series, does not smooth the landslide signal, and uses exactly defined landslide signal thresholds.
Tree-ring based chronologies of slide movements can serve as an important basis for determining landslide activity, assessing risk and triggers, or potentially predicting future landslide behaviour. Unfortunately, however, the landslide areas studied are often affected by another type of slope movement, namely creep, which can introduce a considerable amount of noise into the resulting chronology. Thus, this study focused on testing different dendrogeomorphic approaches for the extraction of landslide signal from tree-ring series with respect to their ability to filter out the influence of creep movements and slide movements. For this purpose, 45 trees (Fagus sylvatica L. and Acer pseudoplatanus L.) growing on the steep slope of a sub-landslide block whose movement has been monitored for a long time and for which a single landslide event is known (second half of 2010) were sampled.
The first tested approach was based on changing tree-ring eccentricity values and has shown its very high sensitivity to all slope movements and is therefore not applicable for creep filtering and slide movements unsuitable on steep slopes. The second approach, using macroscopic identification of the tension tree, proved to be the most suitable, accurately detecting the slide event and successfully filtering out all creep-induced noise. A final approach based on the detection of sudden anatomical changes in tree rings (independent of the presence of tension wood) also captured high amounts of noise and also slide event. Its use would be possible in the case of a suitably set event-response index threshold. The study also includes a discussion of the general effect of creep movements on tree growth, the limitations and advantages of each approach, and recommendations for future research.
Understanding hydrometeorological triggers of natural hazards through dendrogeomorphology: Methods, limitations, and challenges
2023, Earth-Science ReviewsDendrogeomorphology, the dating of geomorphic activity using tree-ring records, is widely employed in forested landscapes impacted by natural hazards, often applied to identify the primary hydrometeorological triggers of such activity. However, the climate background of these papers is frequently imbalanced and necessitates attention and a comprehensive review of the methods and data utilized. This study reviewed 121 papers analysing landslide, debris flow, and snow avalanche reconstructions in conjunction with climate variables. The review assessed the spatial distribution of study sites, uncertainties in dendrogeomorphic and climate data processing, data interpretation, and statistical analysis. While Central Europe, the European Alps, and North American mountain systems have been extensively studied, several regions such as Northern and Southern Europe, the West coast of North America, South Africa, Patagonia, Australia, and New Zealand are still awaiting similar research. Since dendrogeomorphic reconstructions provide information about the year or season of geomorphic activity rather than the specific date, the search for the correct trigger should primarily rely on probability models to identify the most explanatory climate variables. This aspect of landslide dendrogeomorphic research is currently undervalued compared to studies on debris flows and snow avalanches. Moreover, the models should incorporate relevant data, not limited to extreme daily precipitation, but also accounting for antecedent moisture conditions and the snowpack's impact during snowmelt periods. To avoid potential under- or overestimation of extreme precipitation, researchers must ensure the use of appropriate station data that are close in proximity and altitude to the study site, as cautioned by previous discussions. For regional chronologies of geomorphic activity, it is preferable to utilize climate reanalysis products, which are globally available and provide accurate estimations of climate characteristics at various time scales. Consequently, the creation of extensive tree-ring-based datasets encompassing past-to-present geomorphic activity in different regions, along with well-defined climate-geomorphic linkages, will facilitate the modeling of future natural hazard activity under ongoing climate change.