A quantitative assessment of rockfall influence on forest structure in the Swiss Alps
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ORIGINAL PAPER
A quantitative assessment of rockfall influence on forest structure in the Swiss Alps Christine Moos1 · Nora Khelidj2 · Antoine Guisan2,3 · Heike Lischke4 · Christophe F. Randin1,2,5 Received: 14 July 2020 / Revised: 14 July 2020 / Accepted: 7 September 2020 © The Author(s) 2020
Abstract Forests below rocky cliffs often play a very important role in protecting settlements against rockfall. The structure and development of these forests are expected to be substantially affected by the disturbance of the falling rocks. Knowing about this effect is important to predict the development of protection forests and consider potential effects of the falling blocks in management strategies. The goal of this study is to quantify differences in forest structure depending on rockfall activity in four different sites in the Swiss Alps. For this, we collected data on forest structure in zones of different rockfall activity and derived rockfall impact probabilities based on rockfall simulations. We assessed whether differences in forest structure and signs of rockfall disturbance could be observed between the rockfall zones. We additionally built mixed-effects models to identify the key variables explaining the forest characteristics described by diameter (DBH) and basal area (bA). The forest structure differs between the rockfall zones, however, with varying effects amongst the sites. DBH tends to decrease with increasing rockfall activity, whereas tree density appears to be little impacted by rockfall. For most sites, the number of deposited blocks and the simulated tree impact probability have a significant effect in the models along with the species, whereas for one site, hardly any effect of rockfall was found. Our results, obtained either from direct measurements or modelling, show that rockfall can locally influence the structure of forests, whereas the influence depends on the frequency and intensity of the rockfall disturbance. Impact probabilities obtained by simulations can serve as a good proxy for rockfall disturbances. Keywords Rockfall · Forest structure · Disturbance · Protection forest · Rockfall impact probability
Introduction
Communicated by Claus Bässler. * Christine Moos [email protected] 1
Interdisciplinary Centre for Mountain Research, University of Lausanne, Sion, Switzerland
2
Department of Ecology & Evolution, University of Lausanne, Lausanne, Switzerland
3
Institute of Earth Surface Dynamics, University of Lausanne, Lausanne, Switzerland
4
Dynamic Macroecology, Swiss Federal Institute of Forest, Snow and Landscape Research WSL, Birmensdorf, Switzerland
5
Centre Alpien de Phytogéographie, Champex‑Lac, Switzerland
Rockfall is one of the most frequent and widespread natural hazards in mountain regions and can pose a severe threat to infrastructure and human life. Besides technical protective measures, such as nets or dams, protection forests play a very important role as natural means of protection against rockfall. Trees can stop or deviate falling blocks an
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