Forests under stress: Understanding how species interact and adjust to climate change

To unravel the significance of tree adjustments and interactions in a drying and warming world, the next step is to understand the mechanisms of acclimation and species interactions and relate them to global-scale patterns in natural conditions.

In this project we assessed the physiological processes by which trees adjust and interact among each other under a changing climate, determined the consequences of these processes on forest responses to climatic stresses, and improved our understanding of these effects on forests functioning at a large comprehensive scale.

To reach these objectives, we employed a multidisciplinary and multiscale approach using experimental and observational analyses from the individual tree to the continental scale.

• Didion-Gency et al. highlight that incorporating local interspecific interactions in research on climate impacts could improve our understanding and predictions of forest dynamics.
• Grossiord et al. showed that a warming-driven earlier activity compensate for reduced photosynthesis during dry periods, but only for relatively drought-tolerant species like oak. Current predictions of warming-induced mitigation effects through extended carbon uptake seem incorrect for drought-sensitive species like European beech.
• Didion-Gency et al. found that the combination of hot and dry conditions strongly reduced the ability of trees to take up carbon. However, interspecific interactions mitigated the adverse impacts of extreme climate in oak, thereby highlighting the need to deepen our understanding of the role of species diversity under climate change.
• In Schoenbeck et al., we showed for the first time that rising evaporative demand leads to severe hydraulic damage in trees even when soil water is not limiting, highlighting its rising importance in plant mortality mechanisms in the future.

In addition, in McDowell et al., Charlotte Grossiord contributed to synthesizing knowledge on drought-related tree mortality under a warming and drying atmosphere. The authors highlight that the depletion of plant water and carbon pools is accelerated under rising evaporative demand, but increasing CO₂ can mitigate these impacts.