Effects of varying thinning regimes on carbon uptake, total stem wood growth, and timber production in Norway spruce (Picea abies) stands in southern Finland under the changing climate

Introduction: Based on previous studies, it is assumed that the growth of Norway spruce (Picea abies) in southern Finland (61°N) may decrease under the changing climate due to the increasing soil water deficit, without management. Materials and methods: A process-based ecosystem model was employed to study how varying thinning scenarios (nine different plus one unthinned) may affect the net carbon uptake, total stem wood growth, and timber production in Norway spruce stands on three sites with varying soil water availability under the changing climate. Results and discussion: We found that the carbon uptake and total stem wood growth were lower due to reduced soil moisture. This was especially the case on the site with low water moisture if no thinning was applied. Thinning increased the amount of water infiltrating into the soil profile, as well as the availability of soil water, regardless of the site. The current thinning guidelines (BT (0, 0)) may need to be modified under the changing climate for Norway spruce, especially on sites with poor soil water conditions. On these sites, the thinning scenarios with frequent thinning could simultaneously help to increase the growth rate of trees and to mitigate the negative impacts of increasing soil water deficit on tree growth. On the sites with high soil water availability, the thinning scenarios with moderate intensive thinning or with delayed first thinning may simultaneously provide higher timber yield and carbon stock than if the current thinning recommendations are applied.