Climate change is increasing the frequency of droughts in many areas and particularly in the Northern hemisphere. It has been evidenced that drought is becoming a more significant factor in the decline of forests. Drought affects trees either directly by decreasing their growth or indirectly by increasing their susceptibility to wildfires, and to insect pests and diseases.
Deciduous trees tend to resist drought periods better than conifers as they can drop leaves to reduce their need for water. Among conifers, Norway spruce (Picea abies L. Karst.), one of the most economically and ecologically important forestry species in Europe, has been recognized as being highly sensitive to drought events.
the Swedish trial Nässja (see below). Photo by Mats Berlin, Skogforsk.
The summer drought of 2018 was one of the most climatically severe events in Europe with record‐breaking temperatures and wildfires in many parts of Europe. In Sweden only, a unique outbreak was recorded as up to four million cubic metres of Norway spruce were killed by the spruce bark beetle triggered by the hot summer of 2018. The infestation even continued in 2019 and 2020. Therefore, drought tolerance can be considered as an important trait for successful regeneration and high productivity of Norway spruce.
A recently published study assessed the impact of the 2018 drought on the height growth of Norway spruce using measurements obtained from about 6000 young clones in Sweden and Finland. Results showed that the hot summer of 2018 had negatively influenced height growth of trees in 2018 and also their recovery in 2019, particularly in the Southern Swedish trials. However, we have identified some resistant genotypes having both good growth and drought tolerance capacities.
the Swedish trial Nässja. Photo by Haleh Hayatgheibi, Skogforsk.
In conclusion, given the predicted occurrence of more frequent and severe drought events as well as the high sensitivity of Norway spruce to drought, the resistant genotypes should be selected and incorporated in the future breeding programs of Norway spruce.
Hayatgheibi, H.; Haapanen, M.; Lundströmer, J.; Berlin, M.; Kärkkäinen, K.; Helmersson, A. The Impact of Drought Stress on the Height Growth of Young Norway Spruce Full-Sib and Half-Sib Clonal Trials in Sweden and Finland. Forests 2021, 12, 498. https://doi.org/10.3390/f12040498