Empirical survival model for European beech (Fagus sylvatica L.) seedlings in response to interactive resource gradients and (a-) biotic conditions within an experimental canopy gap study

Abstract

The success of beech regeneration depends on resource availabilities, which are both heterogeneously distributed in forests and influenced by climate change impacts such as drought and heat waves. To ensure beech regeneration success in the future, it is therefore of great interest to understand the influences of different resource availabilities and their potentially interactive effects on beech seedling survival. In an experimental canopy gap study, we investigated the effects of direct (DIRSF) and diffuse (DIFFSF) solar radiation, soil fertility, groundwater influence, micro-site elevation, vegetation and root competition of overstorey trees on the survival of beech seedlings two years after planting in 2017. The inverse of fine root densities found for overstorey beech (BGRB) and oak (BGRO) was interpreted here as an approximation of the availability of below ground resources, mainly soil water. A logistic model demonstrated positive and interactive effects of DIFFSF, BGRB and soil fertility, emphasizing the complementary resource use pattern of beech seedlings. DIRSF showed a negative effect on survival that was enhanced on groundwater-dominated and higher elevated micro-sites and linked to intensified water limitation. The initial stature of seedlings, the presence and biomass of vegetation and BGRO had no significant effects on beech seedling survival. The unexpected extend to which DIFFSF affected beech seedling survival, the given significance of complementary effects of DIFFSF, BGRB and soil fertility, as well as found interactive effects of DIRSF are discussed in the context of the 2018/19 drought event. Our results suggest that silvicultural measures, such as the creation of larger gaps, can significantly improve resource availabilities, providing an opportunity to increase survival of beech seedlings in the face of climate change impacts.