Regional Mountain Conference

Mixed-species regeneration in mountain forest ecosystems results from the availability of seeds, ecological (micro-) site conditions, the interaction of species traits, and environmental variability over extended time periods. Using long-term monitoring data from a mountain forest in the Northern Calcareous Alps, we analysed survival, recruitment and early growth dynamics of natural regeneration under exclusion of herbivory.

From 2015 to 2025, saplings of Picea abies (n=269), Abies alba (n=406), Fagus sylvatica (n=184) and Pinus sylvestris (n=17) were surveyed annually on two fenced plots, 245 and 233 m² in size. The individual-based assessment allowed for analysis of mortality and interannual growth variability of regeneration up to 14 years old.

Across all species, survival probabilities declined at a remarkably steady rate over time, but clear species- and site-specific differences emerged. With a survival rate of around 80%, Fagus sylvatica consistently showed higher survival rates than coniferous species. By contrast, Picea abies exhibited the strongest decline, with a survival rate of around 60%. Abies alba showed intermediate patterns with a survival rate of around 75% within the first 14 years. Relative growth rates varied substantially between years, indicating a general sensitivity of early growth to environmental variability. While individual drought events, such as the one experienced in 2018, had a notable impact on growth rates, they did not result in a general dieback or substantially increased mortality

The results highlight seedling establishment and sapling mortality as a key process shaping regeneration trajectories in mountain forests. Potential drivers for mortality include density-dependent intraspecific competition, micro-site heterogeneity (forest floor properties, soil moisture, snow cover), episodic events such as late frost or drought, and biotic agents including pathogens. Disentangling the relative importance of and interactions between these drivers requires further long-term monitoring and analyses.