The genetic and environmental variance of radial increment in Scots pine of south-eastern Baltic provenances in response to weather extremes

Intensification of weather anomalies, particularly those related to temperature in warming winters and moisture availability, have been identified as the major emerging climatic threats to forest ecosystems in the hemiboreal zone. Considering the large-scale nature of the threats, assisted migration and tree breeding appear as the most promising means for mitigating the climatic risks. However, for successful implementation of such means, information on the genetic control over the weather sensitivity of trees is needed. Local genetic adaptations of populations occur to maximize competitiveness and survival, while the differences in phenotypic plasticity, implying varying genotype by environmental interactions, can be utilized for the acquisition of locally targeted reproductive material. To gain initial (rough) estimates of genetic control and phenotypic plasticity of growth responses to weather anomalies, a set of seven native eastern Baltic provenances differing by productivity in five trials in Latvia and northern Germany were studied. Tree-ring widths were measured for 10–15 trees per provenance per trial. Relative growth changes and pointer year values were calculated to link changes in increment with weather anomalies and to estimate heritability on an annual basis by the methods of quantitative genetics. During the analysed period (1987–2017), four to seven trial- and provenance-specific pointer years (common relative growth changes) were estimated, which were mainly triggered by co-occurring anomalies in moisture availability and winter thermal regime. This implied resilience of the studied trees to singular weather anomalies, suggesting their adaptability. Furthermore, the heritability estimates peaked one to two years after the pointer years, implying that growth recovery and hence resilience rather than resistance was genetically controlled. Still, local variability of pointer years and heritability estimates portrayed explicit phenotypic plasticity of responses, implying the potential for breeding to locally improve weather tolerance of growth. Keywords: Pinus sylvestris; local adaptation; phenotypic plasticity; growth recovery; tree-ring width; pointer years