High genetic connectivity of common juniper in Scandinavia: Implication for management of genetic resources

In recent years, common juniper has been reported to suffer from increasing population decline, fragmentation, low regeneration and climate change across its European range. Despite being an important component of forest communities, it is not included in the broad conservation approach to forest genetic resources management, and comprehensive knowledge of its genetic structure is lacking. Our study aimed to fill this gap by assessing the genetic structure and connectivity pattern across the species' continuous range in Scandinavia and evaluating the potential risk of climate-induced habitat loss. We investigated the genetic structure at 22 populations across Scandinavia using microsatellite markers and spatial genetic approaches, providing the most comprehensive coverage of northern Europe. We observed a lack of genetic structuring, high genetic diversity and weak fine-scale genetic structure in the Scandinavian populations, which likely indicates extensive historical gene flow. However, increased inbreeding in almost all stands, coupled with local disruptions in gene flow, raises concerns about the potential for genetic erosion. Furthermore, using species distribution modelling we predicted an alarming reduction in climatically suitable areas for common juniper throughout the Europe with some minor reductions projected also in Scandinavia. Our results advocate for the establishment of Genetic Conservation Units in Scandinavia to address the eco-genetic risks identified for the species in our study. Considering that neither the species nor the boreal region is adequately represented in the Pan-European strategy for the management of forest genetic resources, our study provides as a basis for initiating conservation activities for common juniper in Scandinavia. • Common juniper is neglected in forest genetic management despite growing pressures. • Low genetic structure across Scandinavia reflects historically effective gene flow. • Scandinavia will remain suitable for juniper until 2100, except of southern Sweden. • Habitat loss in Europe may threaten the species’ genetic connectivity and survival. • Scandinavian populations should be prioritised for genetic monitoring by GCU design.