Not like other conifers: evaluation of phenotypic diversity in British common juniper, Juniperus communis , indicates genetic isolation and local adaptations among remnant populations

Habitat fragmentation and genetic isolation pose threats to the genetic diversity and resilience of natural populations. Protecting the genetic diversity of populations, and the processes that sustain it, optimises their ability to adapt to changing conditions and new threats: conservation efforts with this specific goal are known as “dynamic conservation.” The common juniper, Juniperus communis , is a keystone species that provides habitat and resources for many plants and animals. It is a highly polymorphic species, and across its natural range it grows in a variety of habitats and growth forms. Juniper populations have been shrinking and becoming increasingly fragmented for over a century in the UK and elsewhere in Europe, raising concerns about the genetic diversity present in juniper populations and their ability to adapt to changing conditions, or their adaptive potential. This paper presents an analysis of the partitioning of phenotypic diversity among regions, populations and families from 16 UK populations assessed in a common garden trial. Our findings suggest high phenotypic variation among populations compared to the variation among families within populations, indicating barriers to gene flow between juniper populations, relatively homogenous populations and, consequently, potentially reduced adaptive potential. This information is a useful baseline for conservation managers and can also help to infer the genetic diversity and adaptive potential of populations.