Abstract
Forest dieback because of drought is a global phenomenon threatening particular tree populations. Particularly vulnerable stands are usually located in climatically stressing locations such as xeric sites subjected to seasonal drought. These tree populations show a pronounced loss of vitality, growth decline, and high mortality in response to extreme climate events such as heat waves and droughts. However, dieback events do not uniformly affect stands, with some trees showing higher symptoms of drought vulnerability than other neighboring conspecifics. In this study, we investigated if trees showing different vulnerabilities to dieback showed lower growth rates (Grs) and higher sensitivities to the climate in the past using dendroecology and the Vaganov-Shashkin (VS) process-based growth model. We studied two Pinus pinaster stands with contrasting Grs showing recent dieback in the Iberian System, north-eastern Spain. We compared coexisting declining (D) and non-declining (ND) trees with crown defoliation values above and below the 50% threshold, respectively. The mean growth rate was lower in D than in ND trees in the two stands. The two vigor classes showed a growth divergence prior to the dieback onset and different responsiveness to climate. The ND trees were more responsive to changes in spring water balance and soil moisture than D trees, indicating a loss of growth responsiveness to the climate in stressed trees. Such an interaction between water availability and vigor was reflected by the VS-model simulations, which provided evidence for the observation that growth was mainly limited by low soil moisture in both sites. Such an interaction between water availability and vigor was reflected by the VS-model simulations, which provided evidence for the observation that growth was mainly limited by low soil moisture in both sites. The presented comparisons indicated different stand vulnerabilities to drought contingent on-site conditions. Further research should investigate the role played by environmental conditions and individual features such as access to soil water or hydraulic traits and implement them in process-based growth models to better forecast dieback.
Highlights
In the last decades, accelerated climate warming has caused a reduction in soil moisture, thereby exacerbating drought stress (Trenberth et al, 2014)
The findings are in line with previous studies showing that P. pinaster radial growth is very dependent on sufficient water availability and elevated soil moisture from the prior winter to early summer (Bogino and Bravo, 2008; Camarero et al, 2015b)
We studied recent dieback events in two P. pinaster stands using a retrospective approach and the process-based VS model
Summary
In the last decades, accelerated climate warming has caused a reduction in soil moisture, thereby exacerbating drought stress (Trenberth et al, 2014). Climate-driven forest dieback is expected to increase in extent and severity in climatechange hotspots such as the Mediterranean Basin region, where seasonal changes in water availability limit tree growth and forest productivity (Vicente-Serrano et al, 2014; Gazol et al, 2018). In this region, climate models have forecasted increases in the frequency and intensity of hotter droughts during the 21st century (Giorgi and Lionello, 2008)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
