Fagus sylvatica (European beech) populations in Central Europe are currently expanding their dominance in many forest types. In this study we focused on the spatio-temporal dynamics of beech recruitment as a mechanism for successful expansion. Specifically we investigated: (1) the developmental trend of the tree community composition and spatial pattern in an unmanaged Picea abies-F. sylvatica forest over 37 years, (2) the pattern of decrease in clustering along increasing tree size gradient of beech, and (3) the spatial patterns of beech regeneration in relation to gap-makers. The study was conducted in the Zofín Forest Dynamics Plot, which is part to the Smithsonian Institution's Forest Global Earth Observatory (ForestGEO) as the research plot representing European natural mixed temperate forests. To quantify these dynamics, we used the stem map of trees with DBH ? 10 cm carried out in 1975, 1997, 2008 and a census of trees with DBH ? 1 cm from 2012 to calculate recruitment, growth, mortality and, from those vital rates, population change. Various types of the pair correlation function were applied to the data to describe the tree density variability over time. Our analyses revealed a trend of increasing F. sylvatica representation at the expense of P. abies and Abies alba over the 37 years. Increased clustering of F. sylvatica trees with DBH ? 10 cm correlated with new recruits at plots where F. sylvatica replaced declining P. abies. On the other hand, the decrease in F. sylvatica clustering at some plots was likely due to strong intra-specific competition. The analysis of the spatial patterns of F. sylvatica individuals along DBH gradient 1-9 cm showed a trend of increasing clustering up to 5 m distance. F. sylvatica saplings to 4 cm of DBH were positively spatially correlated with other conspecific individuals, although at larger sizes (DBH 7-9 cm), this relationship reversed to a negative correlation. Analysis of relationships between saplings and gap-makers did not reveal a clear pattern. We concluded that without a coarse-scale disturbance capable of restructuring the community, F. sylvatica will become the only dominant tree species in this forest type. F. sylvatica gradually replaces P. abies through its space occupation strategy because its recruits are already present before a canopy disturbance. Our results indicate that F. sylvatica saplings can grow up to 4 cm DBH under a closed canopy, but require a canopy disturbance to advance to a larger size class.
