Regional climate and site conditions, not species, determine growth and vulnerability to future climate extremes of Central European oaks

Abstract

Central European oak forests face increasing threats from rising temperatures and frequent drought events, challenging the ecological sustainability of dominant species like sessile oak (Quercus petraea). The performance of thermophilous oaks, such as Turkey oak (Q. cerris) and downy oak (Q. pubescens), under these changing conditions remains uncertain. We compared the adaptive potential of sessile and thermophilous oaks based on their growth sensitivity to current climate and projected growth under future CMIP6 scenarios. Using tree-ring analysis and the VS-Lite model, we studied 27 oak populations at 14 sites with mixed species composition across two climatically distinct regions of the Czech Republic: South Moravia (warmer/drier) and the Bohemian Central Uplands (cooler/wetter). We found a strong coherence in growth dynamics among species, indicating that regional climate and site conditions, rather than species identity, primarily shape growth variation. Climate-growth relationships showed signs of temporal shifts, especially a marked increase in the negative effect of spring temperatures (April-June) on growth in South Moravia after 2016. Growth forecasts for the mean climate conditions expected during 2080-2099 under low-emission scenarios indicated moderate growth increases of up to 39%, largely due to a lengthened growing season. However, the model predicted near-zero simulated growth across all species and most sites during future warm-dry extremes, regardless of the emission scenario. These results suggest that the thermophilous oaks will not outperform sessile oak under extreme drought, highlighting that adaptation strategies should mitigate the impact of recurrent extreme events to ensure the future productivity and persistence of Central European oak forests.