Impacts Of Recurrent Dry And Wet Years Alter Long-Term Tree Growth Trajectories

Climate extremes, such as abnormally dry and wet conditions, generate abrupt shifts in tree growth, a situation which is expected to increase under predicted climate conditions. Thus, it is crucial to understand factors determining short- and long-term tree performance in response to higher frequency and intensity of climate extremes.We evaluated how three successive droughts and wet years influenced short- and long-term growth of six dominant Iberian tree species. Within species variation in growth response to repeated dry and wet years was evaluated as a function of individual traits related to resource and water use (diameter at breast height [DBH], wood density [WD] and specific leaf area [SLA]) and tree-to-tree competition across climatically contrasted populations. Furthermore, we assessed how short-term accumulated impacts of the repeated dry and wet years influenced long-term growth performance.All species showed strong short-term growth decreases and enhancements due to repeated dry and wet years. However, patterns of accumulated growth decreases (AcGD) and enhancements (AcGE) across climatically contrasting populations were species-specific. Furthermore, individual trait data were weakly associated with either AcGD or AcGE and the few relevant associations were found for conifers. Intraspecific variations in tree growth responses to repeated climates extremes were large, and not explained by intraspecific variability in SLA and WD. Accumulated impacts of repeated dry and wet years were related to long-term growth trends, showing how the recurrence of climate extremes can determine growth trajectories. The relationships of AcGD and AcGE with long-term growth trends were more common in conifers species.Synthesis. Repeated climate extremes do not only cause short-term growth reductions and enhancements but also determine long-term tree growth trajectories. This result shows how repeated droughts can lead to growth decline. Conifers were more susceptible to the accumulated effects of extreme weather events indicating that in the future, more intense and frequent climate extremes will alter growth performance in forests dominated by these species.