1. Early-warning signals of individual tree mortality based on annual radial growthMaxime Cailleret, Vasilis Dakos, Steven Jansen, Elisabeth M.R. Robert, Tuomas Aakala, Mariano M. Amoroso, Joe A. Antos, Christof Bigler, Harald Bugmann, Marco Caccianaga, Katarina Čufar, Tom Levanič, 2019, izvirni znanstveni članek Povzetek: 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 interannual 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. Ključne besede: tree mortality, ring-width, forest, growth, resilience indicators, drought, biotic agents, variance Objavljeno v DiRROS: 20.07.2022; Ogledov: 876; Prenosov: 537
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2. Low growth resilience to drought is related to future mortality risk in treesLucía De Soto, Maxime Cailleret, Frank Sterck, Steven Jansen, Koen Kramer, Elisabeth M.R. Robert, Tuomas Aakala, Mariano M. Amoroso, Christof Bigler, Jesus Julio Camarero, Katarina Čufar, Tom Levanič, 2020, izvirni znanstveni članek Povzetek: Severe droughts have the potential to reduce forest productivity and trigger tree mortality. Most trees face several drought events during their life and therefore resilience to dry conditions might be crucial to long-term survival. We assess how growth resilience to severe droughts, including its components resistance and recovery, is related to the ability to survive future droughts by using a tree-ring database of surviving and now-dead trees from 118 sites (22 species, >3,500 trees). We find that, across the variety of regions and species sampled, trees that died during water shortages were less resilient to previous non-lethal droughts, relative to coexisting surviving trees of the same species. In angiosperms, drought-related mortality risk is associated with lower resistance (low capacity to reduce impact of the initial drought), while it is related to reduced recovery (low capacity to attain pre-drought growth rates) in gymnosperms. The different resilience strategies in these two taxonomic groups open new avenues to improve our understanding and prediction of drought-induced mortality. Resilience to drought is crucial for tree survival under climate change. Here, DeSoto et al. show that trees that died during drought were less resilient to previous dry events compared to surviving conspecifics, but the resilience strategies differ between angiosperms and gymnosperms. Ključne besede: trees, mortality, gymnosperms, angiosperms, drought, resilience, resistance, recovery Objavljeno v DiRROS: 20.02.2020; Ogledov: 1964; Prenosov: 1203
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