Abstract

Close-to-nature silviculture, based on natural regeneration, provides a suitable framework for the use of wildlings (naturally regenerated seedlings), enabling their direct collection and transplantation. Wildlings are a promising tool for small-scale forestry, difficult terrain, post-disturbance restoration and assisted range expansion, although their establishment success remains insufficiently understood under varying site and physiological conditions. This study evaluated survival and temporal dynamics of vitality of wildlings of Norway spruce, silver fir, and European beech planted in six experimental forest gaps in a temperate Alpine forest (Pohorje Mountains, Slovenia). A total of 162 wildlings were monitored across 12 repeated assessments between 2018 and 2025, combining data on survival, vitality, morphology and environmental conditions. Survival differed strongly among species, with Norway spruce showing the highest survival (59.3%), followed by European beech (50.0%), while silver fir showed markedly lower survival (20.4%). Initial vitality emerged as the primary determinant of survival, whereas the influence of morphological traits was species-specific. Longitudinal analyses revealed contrasting vitality trajectories among species. Norway spruce exhibited a gradual decline consistent with cumulative stress effects, silver fir showed a strongly non-linear, threshold-like decline, and European beech demonstrated improving vitality over time, indicating progressive acclimation to local conditions. Structural traits such as crown development and root collar diameter were important predictors in Norway spruce, growth performance was dominant predictor in silver fir, and crown-related traits were most important in European beech. Models based on truncated trajectories improved model fit while maintaining consistent results, supporting the robustness of these patterns. The results indicate that early establishment acts as a critical filtering stage and suggest that differences in initial wildling quality, phenological status at planting, and biotic stress may contribute to variation in survival among species. In particular, the low survival of silver fir may partly reflect phenological differences associated with elevational transfer. These findings suggest that successful application of wildlings in assisted range expansion and climate-adaptive forest management requires not only appropriate species selection but also careful consideration of seedling quality, planting phenology, and microsite conditions.

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