Positive effects of warming do not compensate growth reduction due to increased aridity in Mediterranean mixed forests

Abstract

Increased winter and early spring temperatures due to climate change can enhance forest productivity due to earlier growth onset in temperate regions. However, drought‐prone forests can be highly vulnerable to the combined effect of high summer temperatures and water stress. Understanding how water stress and rising temperatures along the growing season control tree growth in co‐occurring species with contrasting drought tolerances is key to project climate change effects on forest dynamics. Here, we evaluated the interactive effect of seasonal temperature and water availability on annual radial growth and climate–growth instability over six decades (1951–2015) in three pine species with contrasting drought tolerances (Pinus pinaster, Pinus nigra, and Pinus sylvestris). For this, we retrospectively observed radial tree growth using dendroecological methods and evaluated seasonal temperature and water availability effects by using linear mixed models. Early growing season temperature and water availability had a positive effect on tree growth, but the positive effect of late season temperature was modulated by water availability. Moving time‐window analyses revealed temporal instability in climate–growth relationships. Since the 1980s, pine species showed a higher growth sensitivity to both seasonal temperatures and annual water availability. Furthermore, growth reductions were more pronounced due to increased summer temperatures and reduced precipitation. Our results were similar for the three studied pine species despite their contrasting tolerance to drought. Overall, climate warming effects on pine growth are contingent upon water availability in Mediterranean continental forests. Synchronization among species, climate–growth instability, and negative growth trends suggests an increased vulnerability to drought of Mediterranean pine species in response to ongoing climate change.

Reduced growth sensitivity to water availability as potential indicator of drought-induced tree mortality risk in a Mediterranean Pinus sylvestris L. forest

“…In order to assess the temporal variation of growth sensitivity to water availability in both alive and dead trees we used the mixed effect model described above. The model was fitted to 5-year lagged windows of 20 years (Díaz-Martínez et al, 2023;i.e., 11 time-windows of 20 years with a starting year from 1948 to 1998).…”

Forest structural diversity determines tree growth synchrony in response to climate change

“…At the same time, variations in annual precipitation and late spring frosts are also affecting tree growth and leaf damage (Castagneri et al, 2015;Sangüesa-Barreda et al, 2021;Zohner et al, 2020). Although there is a broad scientific consensus on increased climate-induced tree mortality, the same is not true for tree growth since warming can have antagonistic effects (Allen et al, 2015;Díaz-Martínez et al, 2023). For example, warming can increase tree growth, primarily through CO 2 fertilization and removal of low temperature limitations to photosynthesis, but excess warming may reduce tree growth due to reduced water availability and increased carbon respiration costs (Adams et al, 2009;D'Orangeville et al, 2018;Peñuelas, Ciais, et al, 2017).…”