Flushing phenology and fitness of European beech (Fagus sylvatica L.) provenances from a trial in La Rioja, Spain, segregate according to their climate of origin

•Beech phenology is assessed against growth and survival at its southern range limit.•Phenology segregated according to location of, and elevation at, provenance origin.•Southern, and some central, European provenances performed best.•Early-flushing is positively correlated with the height of 10-year old beech trees.•Surprisingly, local adaptation promotes frost avoidance above drought preemption. European beech (Fagus sylvatica) reaches the south-western limit of its distribution in northern Spain, beyond which the Mediterranean climate is thought to restrict further expansion of the species range. Consequently, current and future climate change in the region is expected to push back the range margin and threaten the survival of local beech populations. In a provenance trial of pan-European beech populations growing under harsh conditions in La Rioja, we tested whether associations between the timing of spring phenology assessed over three years affected the performance of beeches at the site, and whether they exhibited a trade off between growth rate and survival. In particular, we considered whether the relationship between performance under conditions of summer drought and spring frost at the trial site was dependent on the climate at the site of provenance origin. We report that early-flushing provenances from continental climates in the south-east and parts of central Europe were among the tallest after ten years of growth in the trial: for instance from Val di Sella, northern Italy (mean bud burst day 114 and height 173cm); Gotze Delchev, Bulgaria (day 115, height 135cm); and Aarberg, Switzerland (day 118, height 151cm). While late-flushing provenances from maritime climates in northern and western Europe were among the shortest in the trial: for instance from Soignes, Belgium (day 124, height 73cm); Gullmarsberg, Sweden (day 122, height 69cm); and Bathurst Estate, southern England (day 122, height 85cm). There was no evidence that early flushing increased the mortality of trees at the trial site. The large-scale geographical patterns in flushing strategy reflected a trade off between pre-emptive growth before the summer drought and susceptibility to late frosts. Our findings emphasise the need to conserve populations from the range edge in the south of Europe, the Balkans and western Alps, whose combination of early flushing and drought resistance may become desirable traits for the improved future performance of beech in response to climate change