Abstract: Research Highlights: This study determined that treatment “release from competitors”
causes different reactions in selected timber species respective to diametrical growth, in which the
initial size of the tree (diametric class) is important. Also, the growth habit and phenological traits
(defoliation) of the species must be considered, which may have an influence on growth after release.
Background and Objectives: The objective of the study was to analyze the diametric growth of nine
timber species after their release to answer the following questions: (i) Can the diametric growth of the
selected timber species be increased by release? (ii) Does the release cause different responses among
the tree species? (iii) Are other factors important, such as the initial diameter at breast height (DBH)
or the general climate conditions? Materials and Methods: Four-hundred and eighty-eight trees
belonging to nine timber species were selected and monitored over a three-year period. Release was
applied to 197 trees, whereas 251 trees served as control trees to evaluate the response of diametrical
growth. To determine the response of the trees, a linear mixed model (GLMM, R package: LMER4)
was used, which was adjusted by a one-way ANOVA test. Results: All species showed a similar
annual cycle respective to diametric increases, which is due to the per-humid climate in the area.
Precipitation is secondary for the diametric growth because sufficient rainfall occurs throughout year.
What is more important, however, are variations in temperature. However, the species responded
differently to release. This is because the initial DBH and growth habit are more important factors.
Therefore, the species could be classified into three specific groups: Positive, negative and no response
to release. Conclusions: Species which prefer open sites responded positively to release, while shade
tolerant species and species with pronounced phenological traits responded negatively. The initial
DBH was also an important factor for diametric increases. This is because trees of class I (20 cm
to 30 cm DBH) responded positively to the treatment, whereas for bigger or older individuals,
the differences decreased or became negative.