Variation in irradiance, soil features and regeneration patterns in experimental forest canopy gaps

Key message Natural regeneration of beech, maple and fir was investigated in relation to irradiance, ground vegetation and soil features. Seedling establishment may be favoured by creating small and irregular gaps and by successive extension of gaps along the sun-exposed gap edge. Context To successfully manage natural regeneration, it is important to understand the interactions of forest gap micro-climates and soil features. Aim The aim of this study was to identify conditions for successful natural regeneration of European beech, sycamore maple and silver fir in mixed forests. Methods Seedling growth and survival were recorded within and around two artificial gaps, and the relationships to irradiance, ground vegetation and soil features were examined. A simple conceptual model was applied to identify optimal micro-sites for regeneration. Results Ground vegetation hindered the establishment of natural regeneration in the centre of the gaps. Small seedlings of maple and beech were more abundant within the small gap and along gap edges; beech had the highest density on sun-exposed edges and maple on shaded gap edges. Tall beech and maple seedlings were more abundant along sun-exposed gap edges. Greater variability of irradiance in the larger gap contributed to greater micro-site heterogeneity relative to the small gap. Conclusions Seedling establishment may be favoured by creating small and irregular gaps and by successive extension of gaps along the sun-exposed gap edge. Circular gaps with diameters greater than stand height contribute to increased ground vegetation coverage and hinder tree regeneration, including semi-shade tolerant maple and spruce.