Early-warning signals of Individual tree mortality based on annual radial growth
Creators: name: Cailleret, Maxime
name: Dakos, Vasilis
name: Jansen, Steven
name: Robert, Elisabeth M. R.
name: Aakala, Tuomas
name: Amoroso, Mariano M.
name: Antos, Joe A.
name: Caccianaga, Marco
name: Camarero, Jesus-Julio
name: Cherubini, Paolo
name: Coyea, Marie R.
name: Čufar, Katarina
name: Das, Adrian J.
name: Davi, Hendrik
name: Gea-Izquierdo, Guillermo
name: Gillner, Sten
name: Haavik, Laurel J.
name: Hartmann, Henrik
name: Hereş, Ana-Maria
name: Hultine, Kevin R.
name: Janda, Pavel
name: Kane, Jeffrey M.
name: Kharuk, Viachelsav I.
name: Kitzberger, Thomas
name: Klein, Tamir
name: Levanic, Tom
name: Linares, Juan-Carlos
name: Lombardi, Fabio
name: Mäkinen, Harri
name: Mészáros, Ilona
name: Metsaranta, Juha M.
name: Oberhuber, Walter
name: Papadopoulos, Andreas
name: Petritan, Any Mary
name: Sangüesa-Barreda, Gabriel
name: Smith, Jeremy M.
name: Stan, Amanda B.
name: Stojanovic, Dejan B.
name: Suarez, Maria-Laura
name: Svoboda, Miroslav
name: Trotsiuk, Volodymyr
name: Villalba, Ricardo
name: Westwood, Alana R.
name: Wyckoff, Peter H.
name: Martínez-Vilalta, Jordi
name: Bugmann, Harald Karl Matthias
name: Bigler, Christof J.
name: Rohner, Brigitte E.
Publisher: name: Universität Ulm
Year: 2019
Subjects: subject: ring-width
subject: forest
subject: resilience indicators
subject: biotic agents
subject: variance
subject: DDC 580 / Botanical sciences
subject: Trees Mortality
subject: Growth
subject: Droughts
subject: Wald
subject: Wachstum
subject: Dürre
subject: Varianz

description: Tree mortality is a key driver of forest dynamics and its occurrence is projected to increase in the future due to climate change. Despite recent advances in our understanding of the physiological mechanisms leading to death, we still lack robust indicators of mortality risk that could be applied at the individual tree scale. Here, we build on a previous contribution exploring the differences in growth level between trees that died and survived a given mortality event to assess whether changes in temporal autocorrelation, variance, and synchrony in time-series of annual radial growth data can be used as early warning signals of mortality risk. Taking advantage of a unique global ring-width database of 3065 dead trees and 4389 living trees growing together at 198 sites (belonging to 36 gymnosperm and angiosperm species), we analyzed temporal changes in autocorrelation, variance, and synchrony before tree death (diachronic analysis), and also compared these metrics between trees that died and trees that survived a given mortality event (synchronic analysis). Changes in autocorrelation were a poor indicator of mortality risk. However, we found a gradual increase in inter-annual growth variability and a decrease in growth synchrony in the last ∼20 years before mortality of gymnosperms, irrespective of the cause of mortality. These changes could be associated with drought-induced alterations in carbon economy and allocation patterns. In angiosperms, we did not find any consistent changes in any metric. Such lack of any signal might be explained by the relatively high capacity of angiosperms to recover after a stress-induced growth decline. Our analysis provides a robust method for estimating early-warning signals of tree mortality based on annual growth data. In addition to the frequently reported decrease in growth rates, an increase in inter-annual growth variability and a decrease in growth synchrony may be powerful predictors of gymnosperm mortality risk, but not necessarily so for angiosperms.