Provenance Variation in Functional Traits of European Forest Trees: Meta-Analysis Reveals Effects of Taxa and Age Despite Critical Research Gaps

Climate change is driving major transformations in European forests, making it crucial to understand the adaptive potential of tree species. A key aspect of this potential is the intraspecific variation of functional traits, which influences how species respond to environmental change. Previous studies have examined variation across species, regions, age classes, and traits, but trait-specific patterns and their variation across taxa and tree age have been less systematically quantified.

This systematic literature review identified four main approaches to studying intraspecific variation: provenance effects, provenance–environment interaction effects, clinal effects, and transfer effects. Intraspecific variation is widespread, with significant provenance effects in 73% of cases, provenance–environment interactions in 45%, clinal effects in 30%, and transfer effects in 38%. Growth traits dominate research, but other traits—such as reproduction, survival, phenology, plant morphology, plasticity, drought tolerance, and frost tolerance—are highly relevant and show frequent significant effects, though they remain understudied.

Conifers show higher levels of intraspecific variation than broadleaved species. Older trials indicate stronger effects in phenology, growth, morphology, and survival, suggesting that environmental selection accumulates with age. Major knowledge gaps remain in southern and southeastern Europe, where species with high genetic diversity are most vulnerable. These findings emphasize the importance of maintaining and reanalyzing long-term trials, focusing on species and environmental conditions relevant for future climate scenarios to support forest conservation, diversification, and adaptation strategies.