Tree provenance trials are believed to be a valuable tool for assessing the adaptive potential of a population to a changing environment and ultimately for predicting the populations that are best adapted to global warming. Here, the phenotypic plasticity of morphometric traits of needles and lateral shoots of pines growing in a provenance plot in central Poland was examined to assess the inter- and intra-population variability. No significant differences were found in the measured and counted morphometric features, i.e., needle length (NL), cumulative needles length (CNL), thickness (ST), volume (SV) and shoot density (SD), number of needles per 5 cm fragment of shoot (NN), dry weight of needles (NDW) and shoot (SDW), thickness of bark (BT) and wood (WT), pith diameter (PD), and needle dry mass per area (LMA) among three pine populations while accounting for their region of origin (inter-population variability). In terms of the above-mentioned features, individual populations differed significantly from each other, except for NN and ST. We also noticed a positive, significant relationship between LMA and ST in all studied populations and based on Euclidean distances of measurable or counted traits, three population groups were identified. We concluded that LMA, which is commonly used to quantify leaf structure, is helpful in differentiating intra-population variability.

To maintain the ecosystem resilience to large-scale disturbances in managed forests, it is essential to adhere to the principles of close-to-nature silviculture, adapt practices to the traits of natural forest types, and utilize natural processes, including natural regeneration. This study examines the natural regeneration patterns in silver fir (Abies alba Mill.)-dominated forests, analyzing how the stand structure—tree size diversity, species composition, and stand density—affects the regeneration. We analyze the data from four sites in Poland, Germany, and Italy, employing generalized linear and zero-inflated models to evaluate the impact of the management strategies (even- vs. uneven-aged) and forester-controlled stand characteristics (structural diversity, broadleaf species admixture, and stand density) on the probability of regeneration, its density, and the developmental stages (seedling, small sapling, and tall sapling) across a climatic gradient. Our results indicate a significantly higher probability of regeneration in uneven-aged stands, particularly in areas with lower temperatures and lower overall regeneration density. The tree size diversity in the uneven-aged stands favors advancement from juveniles to more developed stages (seedling to sapling) in places with higher aridity. A denser stand layer (higher stand total basal area) leads to a lower density of natural regeneration for all the present species, except silver fir if considered separately, signifying that, by regulating the stand growing stock, we can selectively promote silver fir. A higher admixture of broadleaf species generally decreases the regeneration density across all the species, except in a water-rich site in the Bavarian Alps, where it had a strong positive impact. These findings underscore the complex interactions of forest ecosystems and provide a better understanding required for promoting silver fir regeneration, which is essential for a close-to-nature silviculture under climate change.

Artificial canopy gaps represent an effective tool for promoting natural regeneration, increasing structural diversity in forest ecosystems. However, the influence of specific gap characteristics on regeneration success remains insufficiently understood. This is especially important for the transformation of even-aged, single-layered Scots pine ( Pinus sylvestris L.) stands on oligotrophic sites, where there is a clear need for evidence-based silvicultural recommendations. This study investigated the effects of gap size (0.05 ha vs. 0.30 ha), soil cover type, microtopography, and within-gap position on the establishment and early development of naturally regenerated Scots pine. To assess these factors, generalised additive models were applied to data from a regeneration experiment established in a 98-year-old pine stand during the winter of 2013/2014. Regeneration density was recorded after the 2nd and 8th growing seasons, and in the latter inventory, seedling height and proportions of soil cover types were also measured. Initial findings showed that seedling density in large gaps was over three times higher than in small gaps (3.42 vs. 1.04 seedlings·m ⁻² ). However, after 8 years, this difference had disappeared, and the gap size no longer significantly affected either seedling density or height. Dwarf shrubs and grasses negatively influenced regeneration density, while lichens and litter had a positive effect on seedling density but were negatively associated with seedling height. The results suggest that both gap sizes may be suitable for regeneration cuttings under similar site conditions.