Breaking through beech: A three-decade rise of sycamore in old-growth European forest

• Sycamore regenerated in the close vicinity of other conspecific trees.
• Number of sycamores grew mostly through the increasing of existing clusters.
• Beech trees were mostly distributed randomly.
• Beech recruits were negatively correlated to older conspecific trees.
• The vicinity of the forest road significantly promoted sycamore recruitment.

European beech (Fagus sylvatica) increases its dominance in various forest types in Central Europe. In this context we investigated a very exceptional process, in which beech have been partly outcompeted by sycamore maple (Acer pseudoplatanus) in unmanaged forest without severe disturbances. Main research questions were as follows: (i) How did the spatial patterns of beech and sycamore develop, and can these patterns be described by known spatial models?; (ii) What were the spatial relationships between beech and sycamore?; (iii) Does the spatial relationship of advance regeneration to gap-makers differ for the two species?; (iv) Did the presence of a road influence the spread of the sycamore population?The study was conducted in beech-dominated forest Žákova hora in the central part of the Czech Republic which has been left to spontaneous development for 85 years. We studied long-term forest dynamics using stem position maps of trees with DBH ⩾ 10 cm carried out in 1974, 1995 and 2011. We used standard methods for calculating recruitment, mortality and population change. Various types of the pair correlation function were applied to describe the development of tree spatial patterns.Our results showed that sycamore regenerated in the close vicinity of other conspecific trees. Sycamore recruits were not spatially associated to individual gap makers. Sycamore individuals had a highly clustered distribution, and the number of individuals grew mostly through the increasing of existing clusters. We successfully fitted the Matérn cluster process for sycamore spatial patterns. The radius of the model cluster ranged between 6 and 16 m. By contrast, beech recruits were negatively correlated to older conspecific trees and showed independence or positive correlation to sycamore veterans. The vicinity of the road significantly promoted sycamore recruitment (opposed to the beech). If the sycamore expansion is connected with the vicinity of the road and thickening of existing sycamore clusters only, as our results indicate, then it can be spatially and temporally limited process.

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