Local genetic adaptations among remnant populations of British common juniper, Juniperus communis, indicated by a common garden trial

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, optimizes their ability to adapt to changing conditions and new threats: an approach 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 highly polymorphic, and across its natural range is found in a variety of habitats and diverse 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 remnant populations and their capacity to adapt to changing conditions or 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 homogeneous populations, and therefore potentially reduced adaptive potential. This information is a useful baseline for conservation managers and will help to protect the genetic diversity and adaptive potential of populations.