Adaptive effects of geographic origin on ring-width and radial growth—climate relationships in Pinus nigra Arnold, the European black pine

Key message Radial growth is a fitness related trait that is expected to vary among forest tree populations when habitat conditions change. Yet, the genetic variability of ring-width and radial growth–climate relationships among geographic origins within species is rarely investigated. This is what we analyzed in the European black pine, Pinus nigra J.F. Arnold (1785), a forest tree species widely but patchily distributed. Using four partially replicated common gardens in France, we show that late spring minimum temperatures affect radial growth negatively and early summer precipitations positively across all provenances. In contrast, there was a strong provenance effect on mean ring-widths, as well as high phenotypic plasticity and significant genotype by environment interactions in most provenances and all subspecies. Provenances of the subspecies P.n. subsp. salzmannii often displayed the smallest mean ring widths except in the least fertile common garden. A few provenances of P.n. subsp. pallasiana , P.n. subsp. laricio and P.n. subsp. nigra performed equally well in all common gardens. Climate smart forestry should consider provenance and not just subspecies recommendations for plantations where black pine is not native, either for ecological restoration or timber production. Context Pinus nigra J.F. Arnold (1785), the European black pine, is a forest tree species widely but patchily distributed throughout southern Europe, from isolated locations in North Africa to the Black Sea and Western Asia. While it has been widely used as a plantation species since the mid-nineteenth century because of its rapid growth even on rather poor soils, the effect of geographic origin within genetic lineage on radial growth and climate sensitivity has not yet been assessed. Aims We analyze the effects of geographic origin on radial growth variability and radial growth–climate relationships within four subspecies of the European black pine. Methods Using a tree-ring to climate relationship approach and a 40-year-long chronology, we first estimated how variable the effect of monthly climate was on radial growth, among 16 provenances within four subspecies, in four bioclimatically contrasted common gardens in France. We then used the tree-ring data to estimate genetic and plasticity effects and to test for the existence of genotype by environment interactions. Lastly, we ranked the growth performance of the different subspecies and provenances measured in each common garden. Results There were few differences in climate effects among provenances and subspecies. Late spring minimum temperatures affect radial growth negatively and early summer precipitations positively. The provenance effect on ring-widths was stronger than the subspecies effect. Radial growth phenotypic plasticity was high across the four common gardens and so were genotype by environment interactions in most subspecies. Provenances of the subspecies P.n. subsp. salzmannii often displayed the smallest mean ring widths except in the least fertile test site. Conclusion Provenance, in addition to subspecies variability should be considered in climate-smart forestry practice, whether for ecological restoration and timber production.