Dendrogeomorphology; Boulders; Noise vs. signal; Wind gust; Landslide

Dendrogeomorphic dating is an effective tool for the assessment of past landslide activity. However, some complex landslide areas include zones of accumulated boulders that can represent geotopes with deteriorated conditions for the stable anchoring of tree roots. Under such conditions, wind gusts can easily cause stem tilting and subsequently be a source of growth disturbances and false landslide events. This study evaluated this possible source of uncertainty in tree rings based on the dating of selected flow-like shaped accumulations of boulders in the Outer Western Carpathians. The data from 94 Norway spruce (Picea abies (L.) Karst.) individuals provided evidence of 154 growth disturbances that were fully comparable with the frequency of active landslides. However, geophysical geoelectrical sounding in combination with field mapping suggests that the studied accumulation is stable. Growth disturbances enabled the reconstruction of nine past events, reaching the minimal threshold of the percentage index. Analysis of triggers detected the occurrence of above-average wind gust speeds in event years compared to other years. Moreover, the dated growth disturbances were not present in the reference trees, probably due to the more stable positions of these trees and thus their better resistance to wind forces. Moreover, the duration of growth disturbances in event years was significantly longer than that of disturbances in other years.