Ecological plasticity of responses of radial increment of Scots pine and its potential for breeding: Doctoral thesis for the doctoral degree of doctor of science (Ph.D.) in agriculture, forestry, and veterinary sciences = Parastās priedes radiālā pieauguma reakcijas ekoloģiskais plastiskums un tā selekcijas potenciāls: promocijas darbs doktora grāda (Ph. D.) iegūšanai lauksaimniecības, mežsaimniecības un veterinārās zinātnēs

The accelerating climatic changes are challenging the natural adaptability of tree populations, which inevitably leads to economic and ecological consequences, hence proactive adaptive measures appear crucial for sustaining trees and related organisms, as well as their systems. In the eastern Baltic regions, Scots pine (Pinus sylvestris L.), which is abundant, stress-tolerant, and economically important, is among the species, whose abundance is projected to decrease due to climatic change. Considering the large-scale nature of climatic changes, the mechanisms of adaptation ought to be robust and self-sustaining, which are largely met by tree breeding. Still, considering the unprecedented pace of environmental changes, comprehensive information on the responses of trees and forests is needed for the assessment of the efficiency of the adaptive measures. Furthermore, mitigating the unprecedented changes apparently requires progressive means (e.g. enhanced application of assisted gene transfer), emphasising the necessity for comprehensive knowledge-based evaluation of the situation and potential solutions to comply with the conservative paradigm of conventional forestry. Analysis of wood increment is a highly powerful tool for detailed retrospection of growth patterns and the underlying genetic, physiological, and environmental effects. Under rapid environmental changes, information on the environmental and particularly weather/climatic sensitivity of increment can be highly valuable and complementary to the conventional morphometric traits associated with the sustainability of genotypes. Morphometric traits, which are cumulative product of the conditions in the past, might be simply outdated by the environmental changes, which is backed up by the increasing rankings of the north-transferred genotypes in provenance trials. Under such circumstances, the sensitivity of increment, though should be scrutinized accounting for the shifting/ extending environmental gradients, paying attention to the ecological realism of the estimated relationships. In this thesis, the responsiveness of radial increment of the eastern Baltic Scots pine to weather fluctuations across the regional climatic gradient and the genetic controls over it were assessed by combining methods of time series deconstruction, quantitative wood anatomy, mixed modelling and quantitative genetics. Empirical material was collected in conventionally managed stands and provenance trials spanning from southern Finland to northern Germany. The thesis summarizes the findings of nine peer-reviewed thematically consistent articles mostly published in top-ranked journals. Among the main things, complex meteorological controls of the winter thermal regime and summer moisture regime were estimated over the radial increment across the regional climatic gradient. Still, most of the estimated responses were nonlinear implying their scalability and ecological realism. Regarding the studied genotypes, the sensitivity 3of increment to meteorological conditions was phenotypically plastic, while showing signs of local genetic adaptation, thus suggesting the adaptability of the populations. The plasticity of increment and its responsiveness, which arises from the ability to efficiently redistribute assimilates for growth while ensuring hydraulic efficiency of stemwood, was related to the productivity of the genotypes. Accordingly, the more productive provenances, which originated from lowland coastal Germany and Poland, and thus were north-transferred in Latvia, were more sensitive to meteorological fluctuations, while showing low susceptibility to frost damage, when compared to local genotypes. The weather sensitivity of growth has moderate heritability suggesting potential for improvements by tree breeding. Accordingly, the observed results encourage the application of the northtransferred fast-growing genotypes, particularly for supplementing gene pool of breeding populations.