Predicting drought-induced tree mortality in Swiss beech forests hinges upon predisposing and inciting factors

Repository Description: This repository contains the figures, tables, supplementary material, and code necessary to reproduce the work presented in the manuscript entitled "Predicting drought-induced tree mortality in Swiss beech forests hinges upon predisposing and inciting factors" by Marano Gina, Hiltner Ulrike, Meusburger Katrin, Hands Tom and Bugmann Harald. Abstract The increase in the frequency and severity of drought-induced tree mortality in many Eu-ropean low-elevation forests poses considerable challenges to forest management and re-quires an understanding of its causes. We propose a novel framework for integrating the factors underlying drought-induced tree mortality in a dynamic vegetation model.We evaluate whether this framework accurately reproduces drought-related mortality in six mesic beech-dominated stands in 2018-2020, and over multiple years in a xeric Scots pine-dominated stand in Switzerland. Additionally, we investigate its behavior along a large climatic gradient in central Europe. We employ a three-step approach.First, we evaluate multiple drought indices for capturing tree growth responses to ex-treme drought. We find that in contrast to widespread indices such as SPI and SPEI, the ForClim drought index captures growth responses to drought intensity during summer, the growing period, and annually.Second, we assess in detail the capability of the ForClim soil moisture model to sim-ulate soil water dynamics, comparing it to the mechanistic soil-vegetation-atmosphere model LWFBrook90. The ForClim soil moisture model adequately simulates soil water dynamics, particularly in extreme drought years.Third, based on Manion’s Decline Disease Theory, we develop a novel mortality submodel that combines predisposing and inciting factors. Its integration in ForClim cap-tures drought-induced mortality events in the mesic beech forests as well as the multi-year mortality at the xeric Scots pine-dominated stand. Along a climatic gradient in central Eu-rope, the model provides good quantifications of Potential Natural Vegetation.The novel framework to capture drought-related tree mortality is simple yet produces accurate results. The underlying hypothesis regarding the factors leading to drought-induced tree mortality is promising but requires further tests for its generality.