Gregor Božič

Escalating natural disturbances in Central Europe necessitate restoration strategies that prioritize ecological integrity and adaptive capacity. Over the last decade, Slovenian forests—traditionally managed via close-to-nature silviculture—faced historic damage from a catastrophic 2014 ice storm, followed by extraordinary windthrows (2017, 2018, 2023) and subsequent bark beetle outbreaks. These events have rendered natural regeneration alone insufficient to preserve forest functions within acceptable timeframes.Analyzing Slovenia Forest Service data (2007–2020), this study evaluates the economics of artificial forest restoration across 14 forest management regions. Based on an extensive data analysis conducted by the author (Bozic et al. 2025), we found that €33.6 million was invested to restore 5,353 ha via planting and 457 ha via sowing. Costs were dominated by planting (53%) and protection against game animals (42%). Crucially, natural disasters shifted management dynamics, with disaster-related restoration (planting) rising from 42% pre-2014 to 76% by 2020.These findings advocate for a shift from reactive forest restoration toward proactive forest structures based on two pillars. First, we see the synergy between genetic adaptation of seed sources and nursery production as vital for seedling survival in extreme environments. To mitigate economic burdens, we propose: (1) differentiated co-financing for resilient mixtures; (2) increased use of sowing; (3) systematic investments in forest stability; and (4) fiscal incentives for quality containerized seedlings and protection against wildlife.Second, forest restoration could be operationalized through a systematic five-step framework for future forests, co-developed by the authors (Kovac et al. 2024). By integrating site-specific actions into broader landscape goals, this holistic approach ensures consistent decision-making and equitable promotion of all sustainability components—ecological, social, and economic—by treating stands as building blocks of functional habitats. Adhering to the precautionary principle, the framework integrates: (1) environmental zoning via structured forest planning situation analysis; (2) climate-optimal species selection based on desired future portrayals and specific stand-level goals, such as species mingling; (3) the identification of climate-resilient seed sources and provenances to ensure that seedlings possess the genetic plasticity required for optimal growth and long-term adaptation to specific site conditions over several decades; (4) specialized silvicultural models executed via site-specific planting blueprints; and (5) adaptive monitoring. This path, supported by the author's extensive data analysis (Bozic et al. 2025) and personal field leadership, provides a foundation for a scientifically grounded transition from disaster-related restorations toward resilient, high-value forest ecosystems.

We analysed the scope and costs of forest restoration with planting and sowing in Slovenia for the period 2007 – 2020, which was carried out by the Slovenian Forest Service (SFS). In the 14-year period, forest restoration by planting seedlings was carried out on 5,353 ha of forest areas, the soil preparation for restoration with planting and sowing measure on 3,489 ha, and the sowing measure on 457 ha. In total, 0.5% of the area of managed forests was restored in Slovenia, which on average means 0.04% of the area of managed forests per year. 61% of the forest areas restored with planting (approximately 3,300 hectares of forest) were protected against game damage. During this period, €9,457,562 was spent on seedlings, of which 66% for broadleaves and 34% for conifers. Within the scope of forest restoration with planting, 6,176,099 broadleaf seedlings (51%) and 5,913,388 conifer seedlings (49%) were planted, for a total of 12,089,487 trees. In the period from 2007 to 2020, €33,595,188 was spent on artificial forest restoration measures across the entire territory of Slovenia, with the largest portion going to planting (53%) and protection against game damage (42%), followed by soil preparation (4%) and sowing (1%). In the period under review, the average purchase price (value) of a classic bare-root seedling was €1.19 for broadleaves and €0.52 for conifers, while the average value of a container seedling was €1.96 for broadleaves and €1.67 for conifers. A comparison between the per-hectare restoration costs incurred with planting and the costs incurred with sowing for 14 forest managemet regions in the studied period shows that the cost per hectare for the planting measure is significantly higher (€6,187/ha) than the cost per hectare for the sowing measure (€1,036/ha).

Climate change threatens the role of European forests as a long-term carbon sink. Assisted migration aims to increase the resilience of forest tree populations to climate change, using species-specific climatic limits and local adaptations through transferring seed provenances. We modelled assisted migration scenarios for seven main European tree species and analysed the effects of species and seed provenance selection, accounting for environmental and genetic variations, on the annual above-ground carbon sink of regrowing juvenile forests. To increase forest resilience, coniferous trees need to be replaced by deciduous species over large parts of their distribution. If local seed provenances are used, this would result in a decrease of the current carbon sink (40 TgC yr⁻¹) by 34–41% by 2061–2080. However, if seed provenances adapted to future climates are used, current sinks could be maintained or even increased to 48–60 TgC yr⁻¹.

Changing environmental conditions, disturbances, and escalating demands for forest ecosystem services require foresters to restore present forestlands with new forest generations that will exhibit ecological integrity, diversity, high adaptive capacity, and the ability to provide essential ecosystem services. Establishing such forests requires careful consideration of the forest landscape and site dynamics. In pursuit of these requirements, we developed a novel framework that enables the restoration of forest sites and promotes the desired features of the forest complex at the same time. This framework was designed with the methods of system engineering and was organized in the same way as the forest planning process. It was tested in the habitat type of Illyrian Fagus sylvatica forests belonging to the Natura 2000 network. The environmental, vegetation, and site conditions were investigated via field inspections, available forest management plans, and simple GIS analyses. Additionally, we established a seminatural stand composed of European beech, sessile oak, sycamore maple, silver fir, and some wild fruit tree species. The survival of planted species was assessed using census and simple random sampling, the performance of provenances by Student’s test, while microhabitat factors were explored by a one-way ANOVA. The survival rate of key species was estimated to be 55.6%, while that of fruit species was estimated to be 94.5%. Our framework demonstrated satisfactory performance and contained sufficient benchmarks to facilitate consistent decision-making. In the discussion, we elucidate the framework’s primary features and attributes of the mixed stand, where we also expose some open issues to be addressed in the future.

Key message: Provenance controls conductive area of stem secondary xylem, leaf area, and stable isotope (C, N, and O) ratios of beech leaves, while no significant effects were observed for ectomycorrhizal community composition. Beyond growth parameters and drought tolerance, comparatively little is known about the functioning of different beech (Fagus sylvatica L.) provenances. We investigated properties of leaves, stem secondary xylem, and ectomycorrhiza (ECM), and explored their interdependencies to identify the best performing beech provenance in optimal growth conditions. The study was conducted on 23-year-old trees in a provenance trial. The investigated provenances originated from Atlantic (Belgium—BE), Alpine (Italy—IT, Slovenia—SI), and continental climates (the Czech Republic—CZ). A significant effect of provenance was observed for stem vessel diameters and conductive area, as well as for foliar %C, δ¹³C, δ¹⁵N, and δ¹⁸O. δ¹³C as a proxy of intrinsic water use efficiency (iWUE) showed that the highest iWUE was achieved in BE provenance. Individuals with a better iWUE had wider growth rings regardless of provenance. Better iWUE was associated with lower specific leaf area (SLA). ECM community composition and diversity indices did not differ significantly among the provenances. Specific ECM taxa were associated with individuals with high SLA, δ¹³C, δ¹⁵N, and δ¹⁸O. In optimal growth conditions with no stress events, BE is a promising provenance due to an efficient water conducting system with high vessel diameters and conductive area, and high iWUE, while Alpine provenances showed an adaptation of their water conducting system to freezing conditions at their original locations. Integrating findings from different compartments improves our understanding of functioning of different beech provenances.

Key message: Studied beech provenances showed different patterns of inter-annual variability in mean vessel area and ring widths, indicating influence of intraspecific variability and diverse environment on hydraulic conductivity and carbon storage potential. International provenance trials of ecologically and economically important tree species are crucial to deciphering the influence of environmental factors and intraspecific variability on tree growth and performance under climate change to guide assisted gene flow and assisted migration of tree provenances and species. In this context, we compared inter-annual trends in tree-ring widths (carbon sequestration potential) and vessel characteristics (conductivity optimisation) of four beech provenances in two international provenance trials, one in Slovenia (Kamenski hrib, a core beech growing site) and one in Hungary (Bucsuta, a marginal beech site) in 2009–2019. We found different patterns of inter-annual variability in mean vessel area and tree-ring widths among provenances and sites, pointing to diverse genetic background and environmental influence on these two wood-anatomical traits. The average values of the vessel area varied less between provenances at Kamenski hrib than at Bucsuta. Weather conditions differently affected tree-ring width and mean vessel area. Furthermore, the length of the period of response of vessel area to the analysed weather conditions differed in summer and winter periods. The differences in the mean vessel area within the tree ring were more pronounced in the weather-wise extreme years, regardless of the provenance. Consistent with previous studies, we confirmed that site conditions affect the climate sensitivity of trees, which is more pronounced at marginal sites or in extreme years. The findings on how different environmental conditions affect the radial growth of young beech trees of different origin are very important for future forest management.