Abstract European beech is Central Europe's most widespread broadleaf forest tree. Besides producing highly valued timber, beech forests provide numerous essential regulating, supporting and cultural ecosystem services. However, beech is threatened by increasingly warmer and drier climates, as exemplified by the premature defoliation and crown dieback observed after the recent extreme droughts and heat waves that hit Europe in 2015, 2018 and 2022. Therefore, forest managers are seeking more drought‐tolerant forest species to mitigate drought stress and gradually adapt forests to future climatic conditions. However, studies rarely investigate the intra‐ and interspecific competition of forest trees for water and nutrients at the recruitment phase and how this competition changes under reduced precipitation and warming‐induced spring phenological advance. Here, we studied European beech, sessile oak and small‐leaved linden saplings growing either in monocultures or mixtures of two species in experimental mesocosms. After 1 year of acclimation, the saplings were subjected to precipitation reduction, passive warming during spring or a combination of the two for two subsequent years. In this period, we studied the treatment‐induced changes in leaf physiology, phenology and sapling growth. Precipitation reduction restricted growth and induced higher leaf bulk δ 13 C values for beech and linden indicating a more conservative water use for these species, whereas no effect of this treatment was observed for oak. Beech and oak saplings grew best in interspecific competition with linden, possibly due to both species being more competitive for soil nitrogen sources than linden. However, the exact reason for this remains unclear. In contrast, advanced leaf‐out by warming had no significant effect on water use, nutrient competition or sapling growth. Synthesis : Our results suggest that beech saplings are more drought‐tolerant than previously thought and remain, despite being considerably restricted in growth, strong competitors under reduced precipitation, particularly when growing in beech–linden mixtures. Linden saplings, on the other hand, promoted beech and oaks' shoot and root growth and presumably exacerbated the exposure to soil drought of intra‐ and interspecific competitors. However, as lindens are relatively shade‐tolerant, they may, depending on the location, be equally promising for forest regeneration at sites affected by beech dieback from a forest management perspective than the more drought‐tolerant oak species.
Walde et al. (2026) studied this question.