The Interplay of the Tree and Stand-Level Processes Mediate Drought-Induced Forest Dieback: Evidence from Complementary Remote Sensing and Tree-Ring Approaches

Abstract

Drought-induced forest dieback can lead to a tipping point in community dominance, but the coupled response at the tree and stand-level response has not been properly addressed. New spatially and temporally integrated monitoring approaches that target different biological organization levels are needed. Here, we compared the temporal responses of dendrochronological and spectral indices from 1984 to 2020 at both tree and stand levels, respectively, of a drought-prone Mediterranean Pinus pinea forest currently suffering strong dieback. We test the influence of climate on temporal patterns of tree radial growth, greenness and wetness spectral indices; and we address the influence of major drought episodes on resilience metrics. Tree-ring data and spectral indices followed different spatio-temporal patterns over the study period (1984–2020). Combined information from tree growth and spectral trajectories suggests that a reduction in tree density during the mid-1990s could have promoted tree growth and reduced dieback risk. Additionally, over the last decade, extreme and recurrent droughts have resulted in crown defoliation greater than 40% in most plots since 2019. We found that tree growth and the greenness spectral index were positively related to annual precipitation, while the wetness index was positively related to mean annual temperature. The response to drought, however, was stronger for tree growth than for spectral indices. Our study demonstrates the value of long-term retrospective multiscale analyses including tree and stand-level scales to disentangle mechanisms triggering and driving forest dieback.

Rates of Stemwood Carbon Accumulation Are Linked to Hydroclimate Variability in Mexican Conifers

“…Other limitations of our study are that we reconstructed the radial growth and aboveground woody biomass using general allometric equations, but we lacked detailed data on changes in belowground biomass and species-specific allometric relationships developed for the study sites. Our database nevertheless represents a solid input for adapting new algorithms relating changes in tree biomass and climate (see [16,56,57]) and, if necessary, replicating the analyses in other bioclimatic zones. Another important aspect would be to explore the use of other models such as generalized additive models, which would allow a better understanding of nonlinear influences of the hydroclimate on C capture.…”

Current and future drought vulnerability for three dominant boreal tree species

“…Increasing global temperatures with higher atmospheric evaporative demand are leading to more frequent and severe droughts with a critical impact on human and environmental systems (Hammond et al., 2022; Vicente‐Serrano et al., 2022). Intense and recurrent droughts have resulted in tree‐crown defoliation (Moreno‐Fernández et al., 2022), shifts from carbon sinks to sources (Anderegg et al., 2015; Kannenberg et al., 2020), and growth decline and/or mortality of trees across all forest types (DeSoto et al., 2020; Senf et al., 2020). As a consequence, changes in community structure and species distributions are ongoing (Brodribb et al., 2020).…”

“…The Swedish NFI provides a dense network of plots with tree‐ring data and information on forest characteristics (Fridman et al., 2014), useful for meaningful reconstructions and interpretations of regional‐scale patterns of tree drought responses. Tree radial growth is more sensitive to climate extremes than other variables (Kannenberg et al., 2019; Moreno‐Fernández et al., 2022) and can be used as an early‐warning signal of mortality risk (Cailleret et al., 2017). Cailleret et al.…”

“…Tree radial growth is more sensitive to climate extremes than other variables (Kannenberg et al, 2019;Moreno-Fernández et al, 2022) and can be used as an early-warning signal of mortality risk (Cailleret et al, 2017). Cailleret et al (2019) found that abrupt decreases in annual growth are a robust early-warning signal of tree mortality.…”

Celebrating 25 Years of Ecosystems

“…Three more papers illustrate studies of ecosystem structure and function in response to changing drivers, such as extreme weather and changing disturbance regimes in a warming world. Severe droughts are occurring more frequently and for longer duration in many parts of the world; Moreno-Fernandez and others ( 2022 ) explore drought-induced tree die-off in Mediterranean forests. Storms are also intensifying.…”