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, original scientific article Abstract: 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.
Keywords: tree mortality, ring-width, forest, growth, resilience indicators, drought, biotic agents, variance
Published in DiRROS: 20.07.2022; Views: 610; Downloads: 395
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2. Growth response of different tree species (oaks, beech and pine) from SE Europe to precipitation over timeDejan Stojanović, Tom Levanič, Bratislav Matović, Stefan Stjepanović, Saša Orlović, original scientific article Abstract: Changing climatic conditions can have various consequences for forest ecosystems, from increasing frequencies of forest fires, ice and windstorm events to pathogen outbreaks and mass mortalities. The Standardized Precipitation Index (SPI) was chosen for the evaluation of drought impact on the radial growth of trees after extensive preliminary testing of various calculated monthly climate parameters from the CARPATCLIM database. SPI was calculated for periods between 3 and 36 months for different sites (lowland and mountainous parts of Serbia, Southeast Europe), from which Quercus robur, Q. cerris, Fagus sylvatica and Pinus sylvestris samples were acquired. Bootstrapped Pearson%s correlations between SPI monthly indices and radial growth of tree species were calculated. We found that 12-month SPI for summer months may be a good predictor of positive and negative growth of different species at different sites. The strongest positive correlations for five of six tree-ring width chronologies were between 12-month June and 14-month September SPI, which implies that high growth rates can be expected when the autumn of the previous year, and winter, spring and summer of the current year, are well supplied with precipitation, and vice versa (low precipitation in given period/low growth rates).
Keywords: standardized precipitation index, SPI, climate change, tree mortality, Quercus sp., Fagus sylvatica, Pinus sylvestris
Published in DiRROS: 18.04.2018; Views: 2947; Downloads: 1686
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