Juniperus communis - EUFORGEN European forest genetic resources programme

Genetic summary

Genetic diversity and variation

Within-population genetic diversity tends to be higher than between-population genetic diversity in common juniper. Many individuals show 50% similarity with individuals in the population. This is very low and reflects the high level of diversity in the species; almost all show no more than 70% similarity (Van Der Merwe et al., 2000).

Populations in the UK were found to be highly genetically diverse and varied, with greater within-population genetic diversity. However, southern populations in the UK are declining, fragmented, and have lower genetic variability (Van Der Merwe et al., 2000). Populations in Germany, Norway, Slovakia, and Italy showed high genetic diversity and low genetic differentiation between populations (Reim et al., 2016). Low levels of genetic differentiation were found in Dutch and German populations, but higher genetic differentiation and variation found in Irish populations may indicate they are more isolated (Reim et al., 2016; Jacquemart et al., 2020). Genetic variation has been shown to be high even in small populations in common juniper; this is not unusual for long-lived tree species. However, it does show the significant value even small populations have in their genetic variability (Jacquemart et al., 2020).

Genetic distribution and clustering

Common juniper does not show a correlation between geographic distance and genetic variance across most of its range (Reim et al., 2016). Genetic variation between populations of common juniper may be related to the differing habitats. Genetic clusters and the north/south separation in common juniper in Lithuania were linked with lowland coastal populations displaying significantly higher diversity than mountain populations; differences in genetic diversity between populations were significant only for populations found in very different habitats (Vilcinskas et al., 2016).

Irish and English populations also exhibit some geographic structuring, which could be an indicator of different postglacial migration routes from multiple sources for populations in the British Isles (Jacquemart et al., 2020). Central European populations are derived from historically larger and more related and interconnected populations with higher genetic diversity, and thus do not show geographic structuring like that found in the British Isles (Jacquemart et al., 2020).

Gene flow

High genetic diversity, low genetic differentiation, and the negligible spatial structure of common juniper populations may originate from high gene flow frequency between populations (Reim et al., 2016). However, despite being wind pollinated and a gymnosperm (which typically have higher levels of gene flow than angiosperms), the species is still characterized by short-distance pollen dispersal and has little effective gene flow (Jacquemart et al., 2020).

The bibliographic review was conducted by James Chaplin of the EUFORGEN Secretariat in August 2024.

Further relevant genetic traits

Glacial biogeography evolution

Common juniper was an early colonizer of postglacial landscapes (Van Der Merwe et al., 2000). However, genetic analysis reveals an absence of a correlation between genetic structure and geographical patterns across much of the species' range in central Europe, which suggests a periglacial survival of common juniper (Reim et al., 2016). Common junipers’ tolerance of poor soils, low temperatures, and drought conditions allows it to survive on cold steppe biomes. Therefore, it is one of the few tree species that survived in central Europe during the last glacial maximum (Michalczyk et al., 2010). Its survival in periglacial environments likely also contributed to its high genetic diversity.

The bibliographic review was conducted by James Chaplin of the EUFORGEN Secretariat in August 2024.

Genetic conservation

Threats

Despite a wide distribution, the population of common juniper has been declining for decades and the species is now threatened in many parts of Europe. Small remnant populations and poor natural regeneration are recognized as the main threats to the long-term preservation of the species (Jacquemart et al., 2020). However, typical juniper habitats such as heathlands and calcareous grassland are sharply declining due to land-use change (Reim et al., 2016). The separation of the species into sexes also halves the density of potential pollen donors and seed-producing individuals (Reim et al., 2016).

Existing populations show little natural sexual regeneration and many of them are ageing. In natural populations only around 1% of seeds germinate after up to five winter seasons (Jacquemart et al., 2020). The poor reproductive ability of common juniper and unsuitable local conditions, which offer offspring low chances of survival, explain the excess of aged individuals in populations (Reim et al., 2016). Aging individuals and declining populations are a concern because the proportion of viable seeds produced by female plants reduces as common juniper becomes older (Van Der Merwe et al., 2000). Low regeneration and fragmentation of common juniper populations will impact genetic diversity and genetic structure of the remaining populations (Reim et al., 2016).

Management

Populations of common juniper need to be assessed for genetic diversity and management strategies should be directed to ensuring that the variety of both common and rare habitats is maintained (Vilcinskas et al., 2016). Care of existing habitats and reintroduction of young common juniper plants to existing populations would improve the long-term preservation of this species (Reim et al., 2016). Management actions such as creating openings in old, closed shrub canopies, reducing competition from other species, or protection against herbivores should be considered to optimize seed germination and the survival of the saplings (Jacquemart et al., 2020). Connectivity between populations might be restored by creating linking populations in areas such as field edges or under power-supply lines (Jacquemart et al., 2020).

The bibliographic review was conducted by James Chaplin of the EUFORGEN Secretariat in August 2024.

Juniperus communis
Common juniper

Environmental zones

Status of Juniperus communis conservation in Europe

Genetic summary

Genetic diversity and variation

Genetic distribution and clustering

Gene flow

Further relevant genetic traits

Glacial biogeography evolution

Genetic conservation

Threats

Management

Genetic Characterisation of Juniperus communis and its GCUs

Availability of FRM

Related publications

Conifers Network: Report of the first meeting

Conifers Network: Report of the second and third meeting

Conifers Network: Report of the fourth meeting

Conifers Network: Report of the fifth meeting

Contacts of experts

Further reading

References

Juniperus communisCommon juniper

Environmental zones

Status of Juniperus communis conservation in Europe

Genetic summary

Genetic diversity and variation

Genetic distribution and clustering

Gene flow

Further relevant genetic traits

Glacial biogeography evolution

Genetic conservation

Threats

Management

Genetic Characterisation of Juniperus communis and its GCUs

Availability of FRM

Related publications

Conifers Network: Report of the first meeting

Conifers Network: Report of the second and third meeting

Conifers Network: Report of the fourth meeting

Conifers Network: Report of the fifth meeting

Contacts of experts

Further reading

References

Juniperus communis
Common juniper