Anatomy of Pinus mugo var. mugo as a fundament for annual-ring-based dating of debris flows in the alpine zone

Abstract

Dendrogemorphic methods are a very accurate tool for dating past debris flows. Chronological data are very valuable, especially in the alpine zone, because climate change has a very intense impact on the frequency of debris flows here. However, at the same time, the applicability of dendrogeomorphic methods in this environment is limited by the lack of suitable trees. Shrub-like mountain pine (Pinus mugo var. mugo) is often the only tree species in this environment, however, dating using a classical macroscopic approach including the analysis of annual-ring series is frequently challenging due to difficulties with detection of increment growth disturbances. Thus, this study focuses on the possibility of detecting growth responses of P. mugo to debris flow exposure at the anatomical level.A total of 14 P. mugo specimens were sampled using discs through stem scars. Anatomical analysis was performed on microsections realized in two radial segments on each stem disc (one as a control). In each segment, five consecutive annual rings (two before damage, one damaged and two after damage) were analyzed each divided into early and late wood zones. The results showed a significant reduction in tracheid parameters (cross-sectional area, radial width, and tangential width) in the early wood zone. Another significant anatomical response was found as an increase in the number of radial rays. Possible effects of scar size and shrub age on the intensity of the anatomical response are also discussed. Thus, this study demonstrated the potential applications of anatomical analyses of P. mugo and suggested new possibilities for dating debris flows within the limit zone of applicability of dendrogeomorphological methods.