Abstract
Dendrochronology has been applied around the world over decades to reconstruct historical geomorphological events and climatic conditions. Traditionally, this research has been conducted using trees (conifers as well as broad-leaved trees) but, in the last few decades, several shrub and dwarf shrub species have also been shown to be useful for dendrochronological purposes. This study assesses the potential of mountain avens (Dryas octopetala L.) to provide accurately dated information about past debris-flow events. The study site, the Marlt-Graben debris-fan, is located in South Tyrol (Italy). 119 shrubs from three debris-flow tracks were analyzed. The longest radius of each sample was measured and cross-dated to build two chronologies for each debris-flow track, one for each leveé. Correlations between these chronologies and precipitation and temperature data from five climate stations located in the proximity of the study site were calculated. The cross-dating procedure was complex, but a strict grouping of the samples, based on the specific leveés of the tracks, enabled the construction of mean chronologies for each of the individual slopes. Although the development of a mean chronology for the study area was unsuccessful, the cross-dated ages of the single shrubs allowed us to reconstruct debris-flow events by utilizing the minimum age method. The low climate correlations suggest that micro site conditions strongly influence the growth of this dwarf shrub. Although the results of this study suggest that Dryas octopetala may provide useful dendroecological information, additional information about its growth dynamics is required before this potential can be fully realized.
Highlights
Dendrogeomorphological studies have traditionally used trees, conifers, to gain information about growth conditions and to date possible disturbance events in the past (Shroder, 1980; Stoffel and Bollschweiler, 2009; Gartner and Heinrich, 2013; Brauning et al, 2016)
The main research questions to be answered by this study are: (i) is it possible to cross-date the annual rings of mountain avens to construct a reliable chronology, (ii) does the age distribution of the shrubs correlate with the vegetation cover density, and (iii) does the age of the oldest plant correspond with the minimum time since the last erosive event happened? To this end, this study examined Dryas octopetala growing in three adjacent debris-flow tracks in the “Marlt-Graben”, an active debris flow fan located near Sulden, Italy
The dwarf shrubs on R2-L had the highest number of missing rings (MR)
Summary
Dendrogeomorphological studies have traditionally used trees, conifers, to gain information about growth conditions and to date possible disturbance events in the past (Shroder, 1980; Stoffel and Bollschweiler, 2009; Gartner and Heinrich, 2013; Brauning et al, 2016). Debris flows represent a significant hazard in high mountains, which can be influenced by changing climatic conditions (Li et al, 2018) These flows are triggered by an interplay of various factors, such as a higher influx of water due to extended snow melting or intense and recurrent rainfalls (Costa, 1984; Bacchini and Zannoni, 2003; Stoffel and Huggel, 2012; Owczarek et al, 2013; Most bauer et al, 2018; Prenner et al, 2018). Bollschweiler and Stoffel (2010) suggested that a deeper understanding of past and present events is required before meaningful extrapolations to the future can be made To date, such events have been almost exclusively studied using trees; the only exception is a study by Owczarek et al (2013) using shrubs to recon struct past debris flow events
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