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.

The analysis of population variability usually concerns the adaptability of trees to changing climatic conditions and their timber production possibilities. It is already known that several phenotypic and genotypic features determine the adaptation possibilities of a population and every population of a given species may have different adaptability to climatic conditions. The assimilation apparatus is an important phenotypic feature that has a large impact on the functioning of tree organisms and their adaptability. Scots pine, which covers vast areas of Europe, is a very important species in the context of ecosystems’ sustainability preservation, especially in the era of global warming. Therefore, in our research, the inter-population and individual variability of morpho-anatomical features of shoots and needles were analyzed. Nine national origins of Scots pine (three populations each from northern, western, and central Poland), which are a part of a 50-year provenance experiment, were compared. Fragments of one-year-old shoots (5 cm long) with needles were collected from the top parts of tree crowns. An extensive analysis of the morphological parameters of the needles (length and width, density, dry mass) and the anatomical features of the shoots (thickness, the share of bark, wood, and pith) was performed. Our surveys showed that the differences between populations are much greater than between regions. The western pine populations, which have shown the highest volume of wood per ha, had the thickest shoots but the lowest dry mass. The northern populations, highly valued for the very good technical quality of wood, had thin shoots. Pine trees from central Poland had the highest density and dry mass of needles and the highest share of wood in shoots.