GROWTH RESPONSE IN BOREAL PRODUCTION FORESTS AFTER SINGLE TREE SELECTION Combining dendrochronology and predictive growth modelling

Sammanfattning

Sweden, as a highly forested country, faces challenges in aligning its forest industry with the demands of the European Union, which promotes forest management practices that avoid clearcutting. The research on alternative forest management needs to be complemented by studies on both short- and long-term growth responses in productive boreal forests. This thesis investigates how individual trees in even-aged production forest respond to single-tree selection thinning in southern Sweden, with the aim of investigating growth dynamics under continuous cover forestry. Tree-ring data were collected from two experimental sites (Skogaryd and Remningstorp) on thinned and unthinned plots. A climate-sensitive growth model based on basal area increment (BAI) was developed to predict expected growth under the observed climatic conditions, enabling quantification of growth release as deviations from climate-driven expectations. Results show that thinning effects are strongly scale dependent. No consistent short-term growth response was detected at the stand level within three years after thinning at Skogaryd, whereas a significant increase in growth was observed approximately five years after thinning in Remningstorp. In contrast, individual trees exhibited pronounced and heterogeneous growth responses. Trees experiencing greater competitive release—quantified using a distance-dependent competition index—showed significantly higher post-thinning growth, highlighting the importance of local neighbourhood structure. Climate variables, particularly summer temperature and precipitation explained most interannual variation in growth, but competition significantly influenced deviations from these baseline patterns. Larger trees generally had higher growth, although the relative response to competition was independent of tree size. Overall, the findings demonstrate that growth responses to selection thinning are spatially variable and emerge over different temporal scales. This underscores the importance of integrating climate sensitivity and spatial competition into assessments of alternative forest management systems, as stand-level metrics alone may obscure critical individual-level processes driving long-term forest dynamics.