Past debris-flow and snow avalanche activity was assessed for the Reiselehnrinne (Tyrol, Austria) using growth disturbances in growth-ring series of 372 Norway spruce (Picea abies (L.) Karst.) trees. Determination of events was performed by analyzing (a) the number and (b) intensity of growth disturbances within tree-ring series and (c) the spatial distribution of affected trees. Differentiation of debris flow from snow avalanche events was based on the intra-annual position of scars, callus tissues or tangential rows of traumatic resin ducts, and on the spatial distribution of trees with simultaneous reactions in the tree-ring series. We introduce a weighting factor to substantiate the dating of past process activity in a comprehensive way and to compare individual events as to their intensity and total number of tree-ring responses. The accuracy of the dendrogeomorphic assessment was then evaluated by comparing the reconstructed event frequency with chronologies available for the Reiselehnrinne. Comparison of tree-ring with historical data demonstrated clearly that the reconstructed event frequency contains the majority of past debris flow and snow avalanche events in the Reiselehnrinne, but that dating of events is not always possible, especially if they are clustered in time or have a limited spread on the cone.

This paper illustrates the effects of abrupt stem burial (burial depth *0.5 m) on tree growth in mature (46 ± 8 years) European larch (Larix decidua Mill.) trees. In contrast to the previous research, which was mostly carried out with saplings and on experimental sites where regular aggradation occurred through the transport of sand, this work focuses on the impact of natural, abrupt burial of mature trees with rocks contained in a sandy-silty matrix typical for debris flows in mountainous headwater catchments. The effect of burial is assessed radially and axially within the stem and over almost three decades after burial. The analysis of growth disturbances and their intensity was based on the 143 cross sections (572 growth series) taken at 10-cm intervals from 6 Larix decidua Mill. The results show quite clearly that abrupt burial causes massive suppression of radial growth as compared to pre-event conditions (mean 77 %, min 38 %, max 92 %, SD 7.2 %). The trees sampled were unable to resume pre-burial growth rates even after 25 years, but recovered to reference growth conditions (as measured in undisturbed, local reference trees) after 15 years (min 3 years, max 25 years, SD 9 years). The results differ only insignificantly between different heights along the tree axis and suppression is equally well expressed at different radial positions within the stem.