Growth plasticity of Gymnosperm trees did not avoid declining resilience to soil and atmospheric droughts during the 20th century

Abstract Plasticity in response to environmental drivers can help trees cope with droughts. However, our understanding of the importance of plasticity and physiological adjustments in trees under global change is limited. We examine 20th century growth responses in Gymnosperm trees during (resistance) and following (resilience) years of severe soil and atmospheric droughts occurring in isolation or as compound events. We use high atmospheric vapour pressure deficit (VPD) to select years of atmospheric drought and negative annual values of the Standardised Precipitation-Evapotranspiration Index (SPEI) to select years with a large negative balance between precipitation and evaporation. Sensitivities (i.e., the slopes of the relationships) of resilience to VPD and SPEI changed throughout the 20th century, with the directions of these changes often reversing in the second half of the century. For the 1951-2001 period, variable sensitivities had positive effects on resilience, especially following years of high VPD and compound VPD/SPEI events, avoiding growth losses that would have occurred if sensitivities had remained constant. Despite sensitivity changes, resilience recovered less at the end of the 20th century compared to the beginning of the century. Future adjustments to low SPEI and high VPD are likely to continue to compensate for the trends in climate only partially, leading to further generalised reductions in tree growth of Gymnosperm trees.