Mitigating drought stress in European beech and pedunculate oak: The role of competition reduction

Droughts pose significant threats to forest ecosystems globally. Effective forest management strategies, adapted to local conditions, are needed to mitigate negative drought impacts. One proposed strategy is competition reduction to increase water availability and, as a result, alleviate drought stress. This study investigates the effect of competition intensity on drought stress and tree growth in European beech (Fagus sylvatica) and pedunculate oak (Quercus robur). We deployed 72 point dendrometers, placed along a competition intensity gradient, in National Park Brabantse Wouden (Belgium), to measure daily minimum tree water deficit (TWD_min) as a drought stress proxy and daily radial growth at tree level. Our results revealed species-dependent effects of competition intensity (CI). For European beech, competition reductions positively influenced growth and alleviated (1 ​< ​CI ​< ​2) or aggravated (CI ​< ​0.5) drought stress. For pedunculate oak, competition intensity did not affect drought stress or growth along the investigated gradient. Environmental variables consistently affected TWD_min and growth of both species. Precipitation reduced TWD_min and increased growth, while vapor pressure deficit led to opposite trends. Thus, environmental conditions and competition can play a critical role in forest dynamics, especially in light of climate change. However, reducing competition through increased management efforts does not seem to be a one-size-fits-all solution to alleviating drought stress. Additionally, there seems to be a trade-off between reducing drought stress and improving tree growth in European beech: tree growth continuously benefited from competition reductions, while under low competition (CI ​< ​0.5) drought stress increased. Revisiting or reviving long-term thinning intensity trials encompassing various regions, species, and soil types will be needed to gain comprehensive insights into mitigating drought stress through management interventions under different local stand conditions.