Data from: Adaptation to local climate in a multi-trait space: evidence from silver fir (Abies alba Mill.) populations across a heterogeneous environment

Heterogeneous environments, such as mountainous landscapes, create
spatially varying selection pressure that potentially affects several
traits simultaneously across different life stages, yet little is known
about the general patterns and drivers of adaptation in such complex
settings. We studied silver fir (Abies alba Mill.) populations across
Switzerland and characterized their mountainous landscape using downscaled
historical climate data. We sampled 387 trees from 19 populations and
genotyped them at 374 single-nucleotide polymorphisms (SNPs) to estimate
their demographic distances. Seedling morphology, growth and phenology
traits were recorded in a common garden, and a proxy for water use
efficiency was estimated for adult trees. We tested whether populations
have more strongly diverged at quantitative traits than expected based on
genetic drift alone in a multi-trait framework, and identified potential
environmental drivers of selection. We found two main responses to
selection: (i) populations from warmer and more thermally stable locations
have evolved towards a taller stature, and (ii) the growth timing of
populations evolved towards two extreme strategies, "start early and
grow slowly" or "start late and grow fast", driven by
precipitation seasonality. Populations following the "start early and
grow slowly" strategy had higher water use efficiency and came from
inner Alpine valleys characterized by pronounced summer droughts. Our
results suggest that contrasting adaptive life-history strategies exist in
silver fir across different life stages (seedling to adult), and that some
of the characterized populations may provide suitable seed sources for
tree growth under future climatic conditions.