Adaptation of Norway spruce (Picea abies (L.) Karst.) to current and future climatic conditions

Climate change urges our understanding of the capacity of Norway spruce (Picea abies (L.) Karst.) population to adapt and maintain, and even increase, their growth capacity at the level required to sustain a transition towards a biobased socioeconomic model. Climate change is already anticipated to result in an increase of temperature. Although generally an increase in the average temperature is considered favourable for growth in the boreal climates, it will also consequence in more frequent temperature backlashes and drought. Outbreaks of pests and fungi are often associated with extreme events. Altogether, this exemplifies the need to investigate how Norway spruce may respond to those predicted changes. Second generation material of eastern European origin, in relation to improved Swedish material, performs well in the current climate in southern Sweden, with later bud burst when grown in Sweden as compared to Swedish material. The second generation material is closer to Swedish material in timing of bud burst indicating a land race formation. At frost prone sites trees with late bud burst should be deployed as trees with early bud burst will increase the risk of spring frost related damages. The impact of future climate change on 18 Swedish and Eastern European provenances showed that frost days in southern Sweden are likely to decrease, but as bud burst will occur earlier this is expected to lead to an increased occurrence of spring frost events. Furthermore, above normal temperatures during the latter part of quiescence phase can induce earlier bud burst and lower cold tolerance, hence increase the risk for frost damages in spring. Drought can affect the height growth of trees both during as well as after a drought event. A higher genotype and environment interaction (G x E) was also observed to be high and significant in severely drought-damaged stands, thus drought may be the underlying factor for a stronger G x E and subsequently a change in the ranking of tree genotypes

Model analysis of temperature impact on the Norway spruce provenance specific bud burst and associated risk of frost damage

The annual growth cycle of boreal trees is synchronized with seasonal changes in photoperiod and temperature. A warmer climate can lead to an earlier bud burst and increased risk of frost damage caused by temperature backlashes. In this study we analysed site- and provenance specific responses to interannual variation in temperature, using data from 18 Swedish and East-European provenances of Norway spruce (Picea abies), grown in three different sites in southern Sweden. The temperature sum requirements for bud burst, estimated from the provenance trials, were correlated with the provenance specific place of origin, in terms of latitudinal and longitudinal gradients. Frost damage had a significant effect on tree height development. Earlier timing of bud burst was linked to a higher risk of frost damage, with one of the sites being more prone to spring frost than the other two. The estimated provenance specific temperature sum requirements for bud burst were used to parametrize a temperature sum model of bud burst timing, which was then used together with the ensemble of gridded climate model data (RCP8.5) to assess the climate change impact on bud burst and associated risk of frost damage. In this respect, the simulated timing of bud burst and occurrence of frost events for the periods 2021-2050 and 2071-2100 were compared with 1989-2018. In response to a warmer climate, the total number of frost events in southern Sweden will decrease, while the number of frost events after bud burst will increase due to earlier bud burst timing. The provenance specific assessments of frost risk under climate change can be used for a selection of seed sources in Swedish forestry. In terms of selecting suitable provenances, knowledge on local climate conditions is of importance, as the gridded climate data may differ from local temperature conditions. A comparison with temperature logger data from ten different sites indicated that the gridded temperature data were a good proxy for the daily mean temperatures, but the gridded daily minimum temperatures tended to underestimate the local risk of frost events, in particular at the measurements 0.5 m above ground representing the height of newly established seedlings

The Impact of Drought Stress on the Height Growth of Young Norway Spruce Full-Sib and Half-Sib Clonal Trials in Sweden and Finland

The summer drought of 2018 was one of the most climatically severe events in Europe that led to record-breaking temperatures and wildfires in many parts of Europe. The main objective of this study was to assess the impact of the 2018 drought on the phenotypic and genetic response of Norway spruce height growth using the Standardized Precipitation-Evapotranspiration Index (SPEI). To achieve this, the total cumulative height growth of about 6000 clones from 2016 to 2019 in four full-sib trials in Sweden, aged 6-7 years, and from 2017 to 2019 in two half-sib trials in Finland, aged 8-9 years, were measured. The results indicate that the 2018 drought caused reductions in the increment of trees. Although heritability estimates were similar to other reports for Norway spruce, the additive genetic variance was highly inflated in one of the visibly drought-damaged trials in Southern Sweden. Similarly, the genotype by environment (G x E) interaction was highly significant in the drought-damaged Southern Swedish trials. Both additive genetic and phenotypic correlations obtained between height increments in 2019 and final heights were the weakest in all studied trials, implying that the drought legacies might have influenced the recovery of trees in 2019. We may conclude that the severe drought can be an underlying factor for a strong G x E interaction and changes in the ranking of genotypes. Therefore, a selection of drought-resistant genotypes with a good growth capacity tested in variables sites should be considered as an important criterion for future breeding of Norway spruce

Strategies for deployment of reproductive material under supply limitations - a case study of Norway spruce seed sources in Sweden

The aim of this study was to analyze and compare the performance of Norway spruce seed sources from Swedish stands of East European origin (SweEast) with material from Swedish (SweSO) and East European (EastSO) seed orchards, and with material from Swedish (SweS) and East European (EastS) unimproved stands. The seed sources were field tested at six locations in southern Sweden and assessed for growth and phenology. The assessment of growth traits indicated that trees from SweSO and EastSO had 9-15% greater growth with respect to tree height and diameter in comparison to trees from Swedish local unimproved stands (SweS). Trees from SweEast and EastS showed around 5-7% greater growth. With respect to phenological traits, the expected later bud burst for EastS and EastSO in comparison to SweS, SweSO and SweEast was verified. However, SweEast exhibited earlier bud burst compared to EastS than what could be explained by pollination by Swedish pollen. This was explained by early land race formation for that trait. A strong positive correlation was observed between bud burst and frost damage, which indicates that earlier bud burst does indeed increase the risk of damage from late spring frost at frost-prone sites