Comparison of regeneration and recruitment of shade-tolerant and light-demanding tree species in mixed uneven-aged forests: experiences from the Dinaric region

Research on the early stages of stand dynamics in uneven-aged forests often favours regeneration over recruitment of trees into forest stands. We contrasted both regeneration (i.e. seedlings and saplings existing in a stand) and recruitment (i.e. the number of trees annually crossing the threshold of 10 cm dbh) in two main stand types of uneven-aged forests (plenter and group selection). Data from 1710 permanent plots across the Dinaric Mountains in Slovenia were used to study recruitment; on 165 plots, regeneration was additionally analysed. The zero-inflated negative binomial modelling procedure was applied to identify factors influencing regeneration and recruitment. Total regeneration (30 212 ha(-1)) and that of light-demanding species (14 879 ha(-1)) were abundant. The latter regenerated more successfully in group selection stands compared with plenter stands. A large reduction in regeneration density was determined during its growth, which was more dramatic for light-demanding species (e.g. Acer pseudoplatanus) than for shade-tolerant species (e.g. Fagus sylvatica, Abies alba). The number of recruited trees (5.83 ha(-1) y(-1)) seemed to be sufficient to maintain the uneven structure but was less promising for light-demanding species (0.13 ha(-1) y(-1)). However, light-demanding species have the potential to establish and recruit into uneven-aged stands with a limited target proportion in the growing stock. Both indicators-regeneration and recruitment-are indispensable for understanding patterns of stand dynamics in uneven-aged forests.