Effects of target diameter cutting on oak recruitment in a multilayered mixed conifer-broadleaved stand in southern Sweden

Managing multi-layered forest stands is increasingly promoted as a strategic adaptation measure to climate change. Pedunculate oak (Quercus robur L.) and sessile oak (Q. petraea (Matt.) Liebl.) are ecologically and economically important species and considered important components of future forest management. However, forest management is challenged by the unsuccessful recruitment of oak, particularly under selective cutting systems, due to the species' relatively high light requirements. In this study, we investigated the long-term effects of different selective cutting treatments on oak recruitment in multi-layered mixed stands over 16 years in southern Sweden. We studied the individual tree diameter growth, height growth, and transition of oak recruits into higher canopy positions. All target diameter cutting treatments significantly promoted the individual tree diameter growth of oak recruits, compared to the control. Observed height growth was lower in target diameter cutting treatments. However, target diameter cutting treatments increased the transitions of oak recruits into higher canopy positions. The higher diameter growth and canopy class transitions into higher classes are achieved by the treatment that removed more Norway spruce trees. Therefore, to promote the advancement of oak recruits into higher canopy positions, target diameter cutting could be an appropriate management alternative if it is sufficiently strong and is focused on removing the most competitive tree species.