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

In the Eastern Baltics, climatic changes are expected to alter forest composition favouring broadleaved species. The height growth of trees influences the productivity of stands and the competitiveness of species, particularly in mixed sites, thus emphasising the necessity for accurate projections. Accordingly, height models are paramount for projecting productivity and yields of stands. As tree height growth dynamics vary regionally, regional or even local models are needed. Based upon 214 National Forest Inventory plots and 510 individual canopy trees, dominant height growth for small-leaved lime (Tilia cordata Mill.) and Norway maple (Acer platanoides L.) in Latvia were analysed. Height growth was modelled using a generalised algebraic difference approach, testing several non-linear equations. The Sloboda (for lime) and Hossfeld I (for maple) models showed the best fit and were the most realistic, predicting slower initial and middle-age (maturing period) growth, yet also displayed higher asymptotes compared to Western Europe. The predicted height at the age of 80 years was 14–33 m and 13–34 m for lime and maple, accordingly. A longer establishment period and later growth culmination suggest longer rotation, highlighting the assessment of long-term risks. In this case, supplementation of the models with climatic effects appears advantageous.

The increasing stresses imposed on forests by climatic changes require agile and adaptive management, in which tree breeding plays a crucial role. Assessment of G×E interactions has been highlighted as an explicit source of information for targeted breeding for resilience and productivity via better coupling of the demands of genotypes and locally anticipated climatic changes. Commonly, the genetic effects are evaluated for morphometric traits, which are a cumulative representation of the past conditions. In this study, the variability of increment and its relation to weather fluctuations were addressed as a climate-sensitive functional trait. Parallel Scots pine (Pinus sylvestris) progeny trials representing hemiboreal conditions and a local productivity (edaphic) gradient in Lithuania were studied to evaluate G×E effects on increment, combining tree-ring analysis and quantitative genetics. Scots pine progenies showed low environmental sensitivity of radial increment, which, however, showed complex region-specific relationships with winter temperature and summer moisture regimes. Negligible genetic controls were estimated for the weather sensitivity of increment, yet the genetic controls manifested in response to the co-occurrence of meteorological extremes. The genetic control over increment showed nonlinear relationships with site productivity, being strongest under oligotrophic and eutrophic rather than extremely poor or mesotrophic site conditions. Site productivity showed marginal effects on climatic controls over heritability estimates, indicating weak environmental interactions. Hence, the observed relationships suggest some limited potential for targeted pine breeding based on local populations.