Thinning as the key to more resilient spruce monocultures

A new scientific paper published in the Journal of Forest Science investigates how different thinning intensities impact the growth and stability of spruce forests in the context of a changing climate. The analysis of data from long-term cultivation experiments shows that thinning can significantly improve both the production and resilience of spruce trees; however, the effectiveness of thinning varies based on site conditions.

Photo: Research plot with marked Norway spruce, Velký Blaník, author: Jan Řezáč

This study provides valuable insights for the adaptive management of Norway spruce, which, despite facing challenges such as the bark beetle crisis, remains one of the most important tree species in Central European forestry.

Photo: Norway spruce stand with alder on a waterlogged site, Velký Blaník, author Jan Řezáč

The authors utilised data from three long-term research plots: Blaník, Tetřeví Boudy, and Železná Ruda. These plots underwent various intensities of thinning throughout their development. By conducting dendrochronological analyses of tree rings and calculating resistance indices—such as resistance, resilience, recovery, and average reduction in relative growth—they evaluated how different cultivation methods impacted tree growth and the response of these stands to climatic extremes.

The results indicated that moderate thinning increased production and improved growth stability, while heavy thinning negatively impacted the waterlogged site. Overall, the site itself proved to be a crucial factor. Its influence on growth and resistance was more significant than the variations in thinning intensity. This suggests that there is no universal management approach; the appropriate level of thinning must be tailored to local conditions.

Photo: Norway spruce with varying diameter at breast height (DBH), Velký Blaník, author: Jan Řezáč

Recommendations for practice

• Moderate thinning can enhance the productivity and resilience of Norway spruce monocultures in the face of climate extremes.
• Heavy thinning may pose risks in waterlogged areas and can negatively impact growth stability.
• It is crucial to consider specific site conditions when planning interventions, as there is no one-size-fits-all approach.
• Dendrochronological analyses and resistance indices are valuable tools for evaluating the effects of cultivation measures.
• Adaptive management requires long-term monitoring, experimentation, and the flexibility to adjust procedures as needed.

Photo: Norway spruce stand with birdhouse (biological forest protection), Velký Blaník, author Jan Řezáč

The study confirms that carefully planned and targeted thinning practices can enhance the resilience of Norway spruce monocultures and promote their stability in a changing climate. It is crucial to adjust thinning intensity based on habitat conditions and to monitor stand development over the long term. This information serves as a valuable foundation for adaptive forestry strategies in Central Europe.

The original version of the paper, „Modulating Norway spruce growth and resilience through thinning intensity under climate change conditions“ , can be downloaded here.

Authors: Petra Jablonická, Pavel Horák (Mendelova univerzita v Brně, Lesnická a dřevařská fakulta); Jakub Černý (Výzkumný ústav lesního hospodářství a myslivosti, v. v. i.; Mendelova univerzita v Brně, Lesnická a dřevařská fakulta)

Prepared according original by: Jakub Černý, VÚLHM, v. v. i., e-mail: cerny@vulhmop.cz