Data from: 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 profound transformations in European forests.
Understanding the adaptive potential of tree species is a key challenge
for conservation and adaptation measures. A critical component of this
adaptive potential lies in the intraspecific variation of functional
traits. The long tradition in ecological genetics resulted in a plethora
of studies across species, regions age classes and traits. Prior syntheses
have rarely quantified trait-specific patterns and their variation across
taxa and tree age. We conducted a systematic literature search to examine
intraspecific variation in natural European tree populations. We
identified four approaches to study intraspecific variation (i.e.
provenance-effects, provenance environment interaction-effects,
clinal-effects and transfer-effects). For each approach, we compared their
prevalence to show an effect while also accounting for species, species
group, and age. Our results found that intraspecific variation is common
in European tree species, with tested traits showing significant
provenance effects (73%), provenance environment-interaction effects
(45%), linear clinal-effects (30%) and linear transfer-effects (38%).
While growth traits were predominantly studied, several other traits
showed higher frequencies of significant results. Specifically,
reproduction, survival, phenology, plant morphology, plasticity, drought
and frost tolerance are highly relevant but still understudied in
comparison to growth. Conifer species demonstrated a higher prevalence of
intraspecific variation compared to broadleaves. Despite the research
clearly focusing on young trials, older trials tended to show higher
frequencies of effects in phenology, growth, plant morphology and
survival, suggesting accumulating environmental selection with growing
tree age. Europe lacks essential information on intraspecific variation of
tree species for the diversification, conservation and adaptation of its
forests, especially in southern and south-eastern parts, where many
species harbor high genetic diversity and are most vulnerable. The
significant influence of age urges for a reanalysis, reestablishment, and
maintenance of long-term trials. These trials should consider species and
environmental conditions relevant for future scenarios.