Information about tree biomass is important not only in the assessment of wood resources but also in the process of preparing forest management plans, as well as for estimating carbon stocks and their flow in forest ecosystems. The study aimed to develop empirical models for determining the dry mass of the aboveground parts of black locust trees and their components (stem, branches, and leaves). The research was carried out based on data collected in 13 stands (a total of 38 sample trees) of black locust located in western Poland. The model system was developed based on multivariate mixed-effect models using two approaches. In the first approach, biomass components and tree height were defined as dependent variables, while diameter at breast height was used as an independent variable. In the second approach, biomass components and diameter at breast height were dependent variables and tree height was defined as the independent variable. Both approaches enable the fixed-effect and cross-model random-effect prediction of aboveground dry biomass components of black locust. Cross-model random-effect prediction was obtained using additional measurements of two extreme trees, defined as trees characterized by the smallest and largest diameter at breast height in sample plot. This type of prediction is more precise (root mean square error for stem dry biomass for both approaches equals 77.603 and 188.139, respectively) than that of fixed-effects prediction (root mean square error for stem dry biomass for both approaches equals 238.716 and 206.933, respectively). The use of height as an independent variable increases the possibility of the practical application of the proposed solutions using remote data sources.

Bark constitutes one of the main residues and by-products of the timber harvest. Therefore, in order to conduct effective forest management, it is essential to estimate the possible amount of that product, which can be obtained during the harvest process. Our objective was to develop a model to estimate bark volume and bark volume fraction (i.e., its share in the total volume of a tree). For the study, we choose larch (Larix sp.) which is a rare but valuable forest raw material in Poland. The research material was collected in northern (2 sites), central (1 site), and southern (2 sites) in Poland. In total, we obtained data from nearly 600 trees growing on oligo-, meso-, and eutrophic sites. We used the tree’s breast height diameter, height, and total volume as independent variables. Both analyzed bark parameters varied significantly with regard to location, site type, and age class. Bark volume is strongly and significantly dependent on the tree’s breast height diameter, height, and total volume. For bark volume fraction, this correlation is significant but very weak. The best results of bark volume estimation are achieved for the model with total tree volume as an independent variable. Because of the strong effect of location on bark volume estimates, it is recommended to elaborate locally-based models for this parameter determination.

The use of non-wood forest products plays a significant role in sustainable development, especially in the context of regional development. One of the most important and promising raw materials is birch sap, which in European conditions is obtained mainly from silver birch (Betula pendula Roth). Research on the utility value of birch sap and the influence of a number of factors on its efficiency and quality has been carried out in many research centers, but so far, there are not many studies on the variability of such parameters as a function of time, taking into account the entire period of sap leakage. This research was carried out in birch stands of approximately 80 years in three forest site types: mixed coniferous forest, mixed broadleaved forest, and broadleaved forest. In each site, nine sample trees were selected using Hartig’s method. The daily and all-season sap yield obtained from individual trees was statistically characterized. The relationship between birch sap yield and select quantitative (tree height, absolute and relative crown length, and slenderness) and qualitative (forest site type, tree thickness class, and sap harvesting period) variables was examined. For the first time in the literature on the subject, there is a proposal to distinguish the phases of obtaining birch sap, which may bring new knowledge, both in relation to daily productivity and the quality of the sap. As a result, the smallest amount of sap was found in the initial leak phase, a slightly higher amount was found in the final phase, and the largest amount was found in the main phase. Regarding the forest site type and the interaction between the collection phase and forest site type, no statistically significant relationship with the average amount of obtained sap was found.

One adaptive silvicultural strategy to address the increasing frequency and severity of climate extremes is the promotion of genetic material best suited to a changing environment. Using a long-term provenance trial established in 1966 in central Poland, we evaluated how climate humidity at the parental site (provenance origin) influences individual-tree growth–drought resilience trade-offs in Scots pine (Pinus sylvestris L.). Stem discs from 240 trees representing 16 provenances were initially assessed, of which 202 trees were retained following cross-dating and quality control. Drought responses were quantified using complementary growth resilience indices for major drought events identified using the Standardized Precipitation–Evapotranspiration Index. Mixed-effects models followed by Type III Wald chi-square tests and Sidák-adjusted pairwise comparisons revealed significant provenance-level differences in drought responses. Structural equation modeling showed that parental-site climate directly and indirectly affected drought resistance through its influence on relative tree size. Trees from provenances originating in more water-rich environments tended to be smaller but exhibited higher resistance, indicating a potential trade-off between growth and drought tolerance. Relative tree size was also negatively associated with resilience, whereas recovery and relative resilience were not significantly associated with provenance climate or relative tree size. These findings indicate that provenance climate is associated with drought resistance in Scots pine, with tree size emerging as an important mediator of this relationship.