Growth of Sorbus torminalis after release from prolonged suppression

Key message Continuously suppressed S. torminalis trees were found to be highly sensitive to release cuttings. After release diameter growth increased drastically, the crown redensified from the inside and seeds were produced during the first growing season. Abstract Sorbus torminalis is valued for its timber characteristics and ecological role in cultural landscapes. Due to its increased drought tolerance, the species is of growing interest in the context of silviculturally driven climate change adaptation measures. Due to its comparably slow growth, it often forms a second canopy layer below other deciduous tree species. With regard to its ecological and economic value, forest practitioners need to know whether releasing these continuously suppressed individuals from competition is worth it. Therefore, the objective of this study was to examine the effect of release cuttings on the crown growth and radial increment of S. torminalis heavily suppressed by surrounding sessile oaks ( Quercus petraea ). We observed changes of shoot and diameter growth within the first year following release cuttings. The overall average annual shoot growth more than tripled when compared to pre-release growth patterns (from 1.9 to 6.2 cm). The greatest release effects were found in the inner part of the crown. The majority of the shoots forming the crown periphery developed fruits and showed only restrained increment. Crown redensification from inside was accompanied by the development of epicormic branches in previously branch-free bole sections. Following release cuttings, diameter growth increased by several orders of magnitude. Altogether, release cuttings seem to have a very positive effect on the vitality of continuously suppressed S. torminalis trees. All released trees grew vigorously and developed fruits throughout the crown surface. Thus, release cuttings may facilitate species propagation and reduce inbreeding effects.