Swift adjustment of biomass allocation strategies in Scots pine after thinning

Our study aimed to evaluate the short-term effects of thinning in Scots pine (Pinus sylvestris L.) forests, with focus on above-ground biomass and allocation patterns within trees to compare between treatments. We have established four treatments: one control (unthinned), two moderate thinnings (from above and from below) and one heavy thinning from below, which were properly replicated across four blocks located at two sites in central Sweden. In addition to tree measurements in the field, we performed two destructive samplings, one before thinning in 2020 and another one three years after thinning (2023). We created above-ground biomass functions for each assessment and tree compartment, as well as leaf area and sapwood area functions, which were used for prediction of those variables for treatment effect comparisons on stand level. We found that, within three years after thinning, the dominant trees in the heavily thinned plots presented a significantly higher diameter at breast height (dbh) and leaf area increment, in addition to an increased leaf area-to-sapwood area ratio, than the control. These results indicate that Scots pine trees were able to quickly adjust their allocation strategies under intensive forest management, at least in the short-term, which further suggests that thinning can be a useful strategy in times of climate change and future extreme droughts, when adaptations would be necessary for retaining vital forests.