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The breeding of forest tree species in the Baltic region has notably contributed to wood production for the bioeconomy. Growth modelling is used for long-term estimates of forest development. However, usually based on data from unimproved stands, they may underestimate the growth of improved trees. Accordingly, it is important to identify and integrate the altered stand dynamics associated with improved planting stock into existing growth models to accurately capture the resulting gains or, alternatively, develop new functions specifically designed for improved trees. We used the generalized algebraic difference approach to model and analyze height growth patterns of Scots pine and silver birch with different genetic improvement levels (improved forest reproductive material categories 'qualified' and 'tested'). Modelling was based on 14 260 and 55 926 height–age series from open-pollinated progeny trials in Latvia and Lithuania with an age range of 3–46 and 5–22 years for pine and birch, respectively. Dynamic generalized algebraic difference approach forms of commonly applied height growth functions with forest reproductive material-category-specific sets of coefficients were tested. The dynamic form of the Chapman–Richards and King–Prodan equations had the best fit for Scots pine and silver birch, respectively. The expected height growth of the category 'tested' was slightly better than the one for 'qualified', with more distinct differences in silver birch. The model with forest reproductive material-category-specific coefficients reflected the actual growth of improved trees; however, such application is limited to sites with medium and high site indices, where improved planting stock is typically used. We recommend the model for young stands up to the age of 20 and 40 years for pine and birch, respectively, considering the empirical data cover on which the functions are based. A unified dynamic height model with the same functional form but category-specific parameterization for different improvement levels allows a practical applicability and effective communication amongst diverse users, thereby promoting the utilization of the model amongst forest owners and managers who possess information regarding the origin of planting stock. [ABSTRACT FROM AUTHOR]

In the Baltics, warming is expected to burden the growth of Norway spruce Picea abies, with weather anomalies/extremes having strong triggering effects, which can be mitigated by tree breeding. Within the region, breeding programmes have been aiming for productivity, yet being conservative, their sustainability depends on the adaptability of native genotypes, which is unclear. The adaptability of genotypes can be assessed through local adaptations and phenotypic plasticity, with the sensitivity of increment depicting the conformity of genotypes and environments. To assess the adaptability of native populations to anticipated climates, local genetic adaptation and phenotypic plasticity of the weather sensitivity of the radial increment were assessed by the methods of time series analysis and quantitative genetics based on three clonal trials (low-density single-tree plot plantations of grafted clones of native plus trees) representing the local climatic gradient in Latvia. The growth of trees was sensitive to the moisture availability in summer and the thermal regime in winter, yet coinciding anomalies in both were associated with abrupt changes in tree ring width. These environmental effects differed among the clones, indicating genetic controls over the sensitivity of increment, which, however, decreased under a warmer climate, suggesting a limited adaptability of local populations to warming. Still, the weather-growth relationships showed moderate phenotypic plasticity, suggesting some mid-term adaptability. Accordingly, supplementation of breeding populations via assisted gene transfer with the genotypes that are adapted to warmer and drier climates appears crucial. [ABSTRACT FROM AUTHOR]

The increasing extreme weather and climate events have a significant impact on the resistance and resilience of Norway spruce trees. The responses and adaptation of individual trees to certain factors can be assessed through the tree breeding programmes. Tree breeding programmes combined with multispectral unmanned aircraft vehicle (UAV) platforms may assist in acquiring regular information of individual traits from large areas of progeny trials. Therefore, the aim of this study was to investigate the vegetation indices (VI) to detect the early stages of tree stress in Norway spruce stands under prolonged drought and summer heatwave. Eight plots within four stands throughout the vegetation season of 2021 were monitored by assessing spectral differences of tree health classes (Healthy, Crown damage, New crown damage, Dead trees, Stem damage, Root rot). From all tested VI, our models showed a moderate marginal R2 and total explanatory power—for Normalized Difference Red-edge Index (NDRE), marginal R2 was 0.26, and conditional R2 was 0.49 (p < 0.001); for Normalized Difference Vegetation Index (NDVI), marginal R2 was 0.34, and conditional R2 was 0.60 (p < 0.001); for Red Green Index (RGI), marginal R2 was 0.36, and conditional R2 was 0.55 (p < 0.001); while for Chlorophyll Index (CI), marginal R2 was 0.27, and conditional R2 was 0.49 (p < 0.001). The reliability of the identification of tree health classes for selected VI was weak to fair (overall classification accuracy ranged from 34.4% to 56.8%, kappa coefficients ranged from 0.09 to 0.34) if six classes were assessed, and moderate to substantial (overall classification accuracy ranged from 71.1% to 89.6% and kappa coefficient from 0.39 to 0.71) if two classes (Crown damage and Healthy trees) were tested. [ABSTRACT FROM AUTHOR]

Increasing resistance against biotic and abiotic factors is an important goal of forest tree breeding. The aim of the present study was to develop a root rot resistance index for Scots pine breeding and evaluate its effectiveness. The productivity, branch diameter, branchiness, stem straightness, spike knots, and damage from natural infection of root rot in 154 Scots pine open-pollinated families from Latvia were evaluated through a progeny field trial at the age of 38 years. Trees with decline symptoms were sampled for fungal isolations. Based on this information and kriging estimates of root rot, 35 affected areas (average size: 108 m2; total 28% from the 1.5 ha trial) were delineated. Resistance index of a single tree was formed based on family adjusted proportion of live to infected trees and distance to the center of affected area. Heritability for resistance to root rot based on the value of this index, was high (0.37) and comparable to indices of growth traits. Correlations of family breeding estimates between resistance to root rot and the other traits were not significant, except for a weak, yet significant, positive correlation with diameter at breast height and branch diameter. Selection index including only growth traits (height and stem volume) had a negligible effect on damage by root rot. We detected a maximum genetic gain in resistance index of 33.7% when incorporating it into the selection index with positive gains for growth traits (6.5–11.0%). Two-stage selection with prior selection of the most resistant families was not superior to the use of selection index with only rot resistance included. Overall; rot resistance index appeared to be an effective tool in tree breeding for the selection of more resistant families, using the existing trials with natural (uncontrolled) infection [ABSTRACT FROM AUTHOR]