Testing dendrogeomorphic approaches and thresholds to reconstruct snow avalanche activity in the Făgăraş Mountains (Romanian Carpathians)

Snow avalanches are a widespread natural phenomenon in steep mountain environments, where they modulate landscapes and frequently disturb forest stands. Such disturbances in trees have been used since the 1970s to retrospectively date avalanches, study their extent and reach, as well as to document their triggers. Although virtually every dendrogeomorphic paper is still based on the concepts established by Shroder (1978), important methodological improvements have been achieved in the field ever since and more particularly over the last decade. This study therefore reports on recent methodological progress and employs three different approaches (i.e. Shroder index value and Kogelnig-Mayer weighted index value) and different sets of signals in trees (i.e. inclusion of tangential rows of traumatic resin ducts as evidence of past avalanching) to record snow avalanche activity. Using 238 increment cores from 105 Picea abies (L.) Karst trees which colonize a snow avalanche path in the Romanian Carpathians, we illustrate possibilities and limitations of the different approaches for the period covered by the chronologies (1852–2013). In addition, we sampled 30 undisturbed P. abies trees from a forest stand north of the avalanche path, where no geomorphic disturbance was identified, so as to build a reference tree-ring chronology. The three avalanche chronologies constructed with the disturbed trees allow identification of past process activity, but results differ quite considerably in terms of avalanche frequency, number of reconstructed events and their temporal distribution. Depending on the approach used, 15 to 20 snow avalanches can be reconstructed, with the best results being obtained in the dataset including tangential rows of traumatic resin ducts. The addition of this anatomical feature, formed after mechanical impact enlarges the number of growth disturbances by 43.5%, and can thus explain the increase of reconstructed avalanches by one-third as compared to the results of the chronology using the “conventional” Shroder approach

Snow avalanche synchronicity derived from a multi-path tree-ring reconstruction in the Făgăraș Mountains (Southern Carpathians, Romania)

Snow avalanches pose a constant threat to human lives, property, and infrastructure in mountainous regions worldwide. To efficiently manage avalanche-related hazards and risks, knowledge of past occurrences is crucial. In many mountain regions, archival records on past events are scarce or even completely missing. Therefore, natural archives, such as tree-rings, are widely used as proxies to build century-long snow avalanche chronologies. However, most dendrogeomorphic studies focus on a small number of sites, providing only path-scale reconstructions with limited significance for a larger area. To overcome this problem, in the present study, we analyzed 17 avalanche paths in a small and relatively homogeneous region located in the F˘ag˘araș Mountains, Southern Carpathians, and documented past snow avalanche activity with dendrogeomorphic techniques. Increment cores extracted from 933 Picea abies trees allowed the reconstruction of a total of 174 snow avalanche years across all investigated paths. At the same time, widespread snow avalanche occurrence was identified in the study area. In years such as 1923, 1929, 1988, 1992, 1995, 1997, 2002, and 2005, more than half of the investigated paths experienced at least a major snow avalanche event. Regarding the frequency of event years, we conclude that the mean recurrence interval of widespread/extreme events is 4.1 years. Finally, this study highlights the importance of investigating multiple avalanche paths in a small, homogeneous area to create a better understanding of snow avalanche activity at path- and mountain range-scale. </p