Crown plasticity and neighborhood interactions of European beech (Fagus sylvatica L.) in an old-growth forest

Competition for canopy space is a process of
major importance in forest dynamics. Although virgin and
old-growth European beech (Fagus sylvatica L.) forests in
Europe have been studied for many years, there are to date
no studies of individual-tree crown plasticity and the way
this is influenced by local neighborhood interactions in
these forests. In this study, we analyzed crown plasticity
and local neighborhood interactions of individual trees in
the upper canopy of the old-growth beech forests of Serrahn,
northeast Germany. In a 2.8-ha sample plot, we
measured crown radii of all upper canopy trees and analyzed
the direction and extent of crown asymmetry. Size,
relative position, and distance of neighboring trees were
used to construct vectors of neighborhood asymmetry
within different distances from target trees. The crowns of
beech trees showed strong morphological plasticity. Mean
absolute and relative displacement of crown centers from
the stem base were 1.95 m and 0.37, respectively. Circular–
circular rank correlation coefficients between the
direction of crown displacement and the direction of
neighborhood pressure showed that trees strongly positioned
their crowns away from local neighbors. Highest
correlation coefficients were obtained when basal area and
relative position of neighboring trees within a radial
distance of 12 m were considered. Clark and Evans index
and Ripley’s K-function showed that crowns were more
regularly distributed than stems. Projected canopy cover
was about 10% higher than canopy cover with simulated
circular crowns. We conclude that the crowns of older
beech trees have a high ability to plastically respond to
changes in the local canopy conditions, enabling very
effective exploitation of canopy space.