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Abstract
General Context: Climate change can positively or negatively affect abiotic and biotic drivers of tree mortality. Process-based models integrating these climatic effects are only seldom used at species distribution scale.Objective: The main objective of this study was to investigate the multi-causal mortality risk of five major European forest tree species across their distribution range from an ecophysiological perspective, to quantify the impact of forest management practices on this risk and to identify threats on the genetic conservation network.Methods: We used the process-based ecophysiological model CASTANEA to simulate the mortality risk of Fagus sylvatica, Quercus petraea, Pinus sylvestris, Pinus pinaster, and Picea abies under current and future climate conditions, while considering local silviculture practices. The mortality risk was assessed by a composite risk index (CRIM) integrating the risks of carbon starvation, hydraulic failure and frost damage. We took into account extreme climatic events with the CRIMmax, computed as the maximum annual value of the CRIM.Results: The physiological processes' contributions to CRIM differed among species: it was mainly driven by hydraulic failure for P. sylvestris and Q. petraea, by frost damage for P. abies, by carbon starvation for P. pinaster, and by a combination of hydraulic failure and frost damage for F. sylvatica. Under future climate, projections showed an increase of CRIM for P. pinaster but a decrease for P. abies, Q. petraea, and F. sylvatica, and little variation for P. sylvestris. Under the harshest future climatic scenario, forest management decreased the mean CRIM of P. sylvestris, increased it for P. abies and P. pinaster and had no major impact for the two broadleaved species. By the year 2100, 38–90% of the European network of gene conservation units are at extinction risk (CRIMmax=1), depending on the species.Conclusions: Using a process-based ecophysiological model allowed us to disentangle the multiple drivers of tree mortality under current and future climates. Taking into account the positive effect of increased CO2 on fertilization and water use efficiency, average mortality risk may increase or decrease in the future depending on species and sites. However, under extreme climatic events, our process-based projections are as pessimistic as those obtained using bioclimatic niche models.
Highlights
Sustainable forest management aims to attain a balance between society’s increasing demands for forest products and services, and the long-term preservation of forest health and biodiversity
Using a composite risk index of mortality (CRIM), we addressed the following issues: (1) How does the risk of mortality in face of drought and frost vary among species and across species’ distribution ranges? We expected CRIM differences between species to emerge from their different sensitivity to the target climatic stress, which is modeled in CASTANEA through species-specific parameters
We focused on five output variables simulated by CASTANEA: (1) the Net Primary Production (NPP) and ring widths to assess the ability of the model to reproduce the bioclimatic niche, (2) the percent loss of conductivity (PLC) as an indicator of risk of hydraulic failure, (3) the NSC content as an indicator of risk of carbon starvation, and (4) the frost damage index (FD)
Summary
Sustainable forest management aims to attain a balance between society’s increasing demands for forest products and services, and the long-term preservation of forest health and biodiversity. Climate change interacts with other global change factors such as nitrogen deposition, atmospheric CO2 concentration increase, 03 pollution, land use, and forest management. These factors may have antagonistic or partially offsetting effects on the physiological functioning of trees and the ecological dynamics of forests (Walther et al, 2002; Begon et al, 2006; Thuiller et al, 2006; Morin et al, 2008; Lindner et al, 2014; Pretzsch et al, 2014; Anderegg et al, 2015). A single climatic driver can have both positive and negative effects on tree performance; this is exemplified by the role of increasing temperature on the advance of leaf phenology (Bigler and Bugmann, 2018), which is expected to increase vegetation length, and to expose plants to higher risk of late frosts (Vitasse et al, 2014)
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