Clonal variation and damage dynamics in Norway spruce: Towards the selection of climate-resilient genotypes

Abstract

Climate change is expected to intensify abiotic and biotic stressors in European forests, making the selection of tree genotypes less susceptible to damage a critical priority for sustainable forestry. We evaluated long-term clonal variation in damage susceptibility and growth performance of Norway spruce (Picea abies (L.) Karst.) in three clonal plantations (aged 50 to 59 years) located in Latvia. More than 2,100 trees representing 20–80 vegetatively propagated clones per site were evaluated. Data on tree growth (height, diameter), green crown ratio, survival, and multiple types of stem damage – stem cracks, bark beetle (Ips typographus) infestation, and cervid browsing damage – were collected during two inventories, 4–9 years apart.

Clonal differences were statistically significant (p < 0.05) for tree diameter and stem crack incidence in all plantations (8–23% of trees affected). Bark beetle damage reached up to 9% of trees and showed clonal variation in one plantation. On average, the length of cracks on the stem was 0.6–1.9 m, depending on the plantation. Survival between inventories exceeded 89% overall but differed among clones in relation to damage incidence. Fast-growing trees tended to have more cracks, but at the clone level, there was no consistent trade-off between productivity and damage incidence. Green crown ratio, a key trait reflecting tree architecture, was significantly associated with damage resistance: trees with a live crown ratio ≥ 70% had markedly lower incidence of cracks and bark beetle attacks.

Several clones combined high growth (up to 26% above plantation mean) with low damage occurrence. These results  demonstrate significant and consistent clonal differences and support the feasibility of selecting productive and stem-damage-resistant genotypes for use under uncertain future climate conditions. In practice, maintaining or selecting crown types that retain ≥ 70% green crown may represent a viable strategy – from both a genetic and silvicultural perspective – for reducing the risk of trunk damage and increasing the climate resilience of spruce plantations.

Keywords: tree breeding; clonal forestry; climate-smart forestry; bark beetle damage; stem cracks; cervid browsing damage