J. For. Sci., X:X | DOI: 10.17221/55/2025-JFS

Modulating Norway spruce growth and resilience through thinning intensity under climate change conditionsOriginal Paper

Petra Jablonická ORCID...¹, Pavel Horák ORCID...¹, Jakub Černý ORCID...^1,2

¹ Department of Silviculture, Faculty of Forestry and Wood Technology, Mendel University in Brno, Brno, Czech Republic

² Department of Silviculture, Forestry and Game Management Research Institute, Opočno, Czech Republic

In recent decades, Norway spruce (Picea abies) stands have become increasingly vulnerable to frequent droughts and associated outbreaks of secondary biotic pests, resulting in significant degradation of forest ecosystems. To preserve their production and ecological functions, it is necessary to apply well-adapted silvicultural practices that mitigate the risk of stand decline. This study examines the effects of two thinning intensities (moderate and heavy) on stand productivity and resilience under varying site conditions. Three long-term research sites with paired differently thinned plots located within and outside the natural range of Norway spruce in the Czech Republic were analysed. Tree-ring width measurements were used to calculate radial growth trends and four resilience indices (resistance, resilience, recovery and average relative growth reduction). Across sites Blaník (BL), Tetřeví Boudy (TB) and Železná Ruda (ZR), basal area increment (BAI) differed significantly between thinning intensities (BL: P = 0.044; TB: P = 0.0076; ZR: P < 0.001), with moderate thinning showing higher BAI at BL and TB, whereas heavy thinning reduced growth at the waterlogged TB site. Site-specific differences in tree growth responses to negative pointer years were evaluated, particularly concerning drought events. Resilience metrics computed for five drought pointer years (1976, 2000, 2003, 2015, 2019) showed no consistent differences between thinning intensities; however, at ZR, heavy thinning yielded higher resilience (Rs) and resistance (Rt) in 2015 and 2019. During drought years, the average relative growth reduction (ARGR) ranged from 3% to 31%, with the lowest values under moderate thinning. Overall, moderate thinning enhanced stand productivity and resilience, whereas heavy thinning had adverse effects at the waterlogged site. These results highlight the need to adapt silvicultural practices to local ecological conditions to ensure long-term stability and productivity.

Keywords: climate-growth relationships; climatic stress; dendroecology; resilience indices; silvicultural treatments; tree-ring analysis

Received: July 20, 2025; Revised: September 10, 2025; Accepted: September 11, 2025; Prepublished online: October 21, 2025