Contrasting Patterns of Local Adaptation and Adaptive Potential Under Climate Change for Old-Growth and Planted Stands of Norway Spruce (Picea abies)

Genetic diversity is a key prerequisite for adaptation to changing environments. Maintaining genetic diversity in forest trees is crucial amid climate change, given their long generation times. Forest management practices can affect the genetic diversity of forest ecosystems through selective felling or reforestation strategies following harvests. To assess how managed forests respond to climate-driven changes, we investigated patterns of genetic diversity and local adaptation by contrasting old-growth and recently planted stands of Norway spruce (Picea abies). We assess both neutral and adaptive genetic variation by sequencing pooled samples collected from 45 first stands across northern Sweden. Our results reveal no significant differences in overall genetic diversity between natural and planted populations, indicating that current forest management practices have not substantially reduced genetic variation. Analyses of adaptive variation demonstrate strong signatures of local adaptation in old-growth populations, with clear correlations between genetic and environmental distances. In contrast, planted stands show weaker adaptive signals and are also at greater risk of non-adaptiveness under future climate scenarios. While current forest management practices preserve much of the neutral genetic diversity necessary for long-term forest health, our findings highlight the importance of conserving and promoting adaptive genetic variation available in old-growth stands to ensure resilience against ongoing climate change.