Finding the winner: Resilience to drought of six oak species in a forest-steppe long-term multi-species trial

Climate change in the steppe and forest-steppe regions of southeastern Central Europe is associated with increasing drought frequency and intensity, which have a negative impact on the water dynamics in forest ecosystems. To better understand the reaction of trees to future climatic events, it is necessary to quantify the responses of trees to past episodes of drought. The specifics of the drought (i.e., occurring in winter, spring or summer, or at annual rates) are a determining factor in the capacity of oaks to recover and achieve pre-drought growth rates. To address the capacity of oaks to face extreme conditions, and thus identify the best species for coping with the future climate, we compared the long-term growth rates and resilience components of 120 trees of six oak species ( Quercus robur , Q. cerris , Q. pubescens, Q. pedunculiflora, Q. rubra, and Q. frainetto ) to drought seasonality in southeastern Romania. We employed the concept of a line of full resilience to compare species responses to extreme drought, and we modeled the resilience components in relation to water availability for different seasons. We found that Q. pedunculiflora and Q. frainetto had the highest growth rates and Q. cerris the lowest growth rate in dry years. Quercus rubra and Q. cerris exhibited the lowest resilience after summer drought, whereas Q. frainetto had the highest capacity to achieve a pre-drought growth level. There were also different degrees of nonlinearity in the relationships between the resilience components and water availability in the oak species in different seasons. With the increase in reforestation needs at the country and European level, one of the most effective management strategies for coping with climate change and extreme events is the careful selection of the species. • Q. pedunculiflora and Q. frainetto have the highest growth rates despite dryness. • Q. rubra and Q. cerris have the lowest resilience after summer drought. • Drought seasonality is a stronger driver of oaks' resilience components. • Oaks have a low resilience to summer and annual drought, but high to spring drought. • Resilience-water availability relationship show varying nonlinearity across species.