Juniperus thurifera - EUFORGEN European forest genetic resources programme

Genetic summary

Genetic diversity and variation

Genetic studies of Spanish juniper reveal high within-population genetic diversity, accounting for about 90% of total genetic variance (Jiménez et al., 2003; Teixeira, Rodriguez-Echeverria, and Nabais, 2015). Populations in Spain show significantly higher genetic diversity and a greater number of private alleles than those in Morocco, suggesting the existence of glacial refugia in the Iberian Peninsula and a loss of diversity during the species’ southward migration to North Africa (Teixeira, Rodriguez-Echeverria, and Nabais, 2015). The lower genetic diversity in Morocco may be the result of bottlenecks, genetic drift, or environmental filtering during colonization (Teixeira, Rodriguez-Echeverria, and Nabais, 2015). The species is notable for being exclusively polyploid, the only such case in the genus Juniperus, which may contribute to its adaptive capacity in semi-arid environments (Teixeira, Rodriguez-Echeverria, and Nabais, 2015).

Genetic distribution and clustering

Genetic studies of Spanish juniper show a clear separation between European and North African populations (Jiménez et al., 2003; Teixeira, Rodriguez-Echeverria, and Nabais, 2015). However, there is evidence of limited gene flow between populations, suggesting occasional dispersal, particularly by migrant thrushes that transport seeds (Teixeira, Rodriguez-Echeverria, and Nabais, 2015). Within Europe, two main genetic groups have been identified, one comprising populations from the Alps, Pyrenees, northern Iberia, and Corsica, and the other from the central Iberian Peninsula (Boratyński et al., 2013). Similarly, analysis in Spain distinguished three population groups, separating north-eastern and southern populations from the rest (Jiménez et al., 2003).

Despite overall genetic differentiation between continents, Spanish juniper has weak population genetic structure, indicating substantial intrapopulation variation and historical gene flow (Teixeira, Rodriguez-Echeverria, and Nabais, 2015). Morphological variability reflects the long-term isolation of some populations (Teixeira, Rodriguez-Echeverria, and Nabais, 2015). In North Africa, Moroccan and Algerian populations have distinct genetic signatures, with Algerian populations showing higher differentiation; this is the result of fragmented populations and geographic barriers from mountain ranges (Boratyński et al., 2013; Taib et al., 2020). Algerian populations appear more genetically similar to European populations than to Moroccan populations, yet still have significant genetic distinctiveness (Taib et al., 2020).

Gene flow

There is limited gene flow between European and North African populations of Spanish juniper, with the Strait of Gibraltar acting as an effective barrier (Teixeira, Rodriguez-Echeverria, and Nabais, 2015). However, weak genetic differentiation is seen within regions because of wind pollination and bird-mediated seed dispersal, which facilitate gene exchange over medium to long distances (Jiménez et al., 2003; Teixeira, Rodriguez-Echeverria, and Nabais, 2015). However, Gene flow still declines sharply with increasing distance between stands, contributing to localized differentiation (Boratyński et al., 2013). The species’ dioecious nature and dual dispersal strategies help maintain high within-population genetic diversity while limiting long-range connectivity.

The bibliographic review was conducted by James Chaplin of the EUFORGEN Secretariat in August 2025.

Further relevant genetic traits

Interspecific taxa dynamics

There are two subspecies of Spanish juniper, subsp. thurifera in Europe and subsp. africana in North Africa (Boratyński et al., 2013; Teixeira, Rodriguez-Echeverria, and Nabais, 2015). Research indicates a common Central European ancestor shared with Greek juniper (Juniperus excelsa), which diverged into western and eastern lineages during the Tertiary (Jiménez et al., 2003). Morphological and genetic analyses confirm distinct clustering of these taxa.

Glacial biogeography evolution

During the Pleistocene, Spanish juniper was widespread across Europe and North Africa, with gene flow occurring between now fragmented populations (Teixeira, Rodriguez-Echeverria, and Nabais, 2015). Glacial–interglacial cycles caused repeated range expansions and contractions, with expansions during cold, dry periods and retreats during warmer interglacials due to competition with angiosperms and pines (Jiménez et al., 2003). The species migrated from Central Europe through France and Spain to North Africa, reaching the Atlas Mountains (Boratyński et al., 2013). Following the last glaciation, its range expanded again during the Holocene (Taib et al., 2020).

The bibliographic review was conducted by James Chaplin of the EUFORGEN Secretariat in August 2025.

Genetic conservation

Threats

The genetic diversity of Spanish juniper is threatened by long-term fragmentation driven by climatic aridification and by human pressures. In North Africa, intense wood harvesting, overexploitation for fuel, and heavy grazing have degraded populations, particularly in Morocco and Algeria, where regeneration is slow and natural seed recruitment is rare (Jiménez et al., 2003; Teixeira, Rodriguez-Echeverria, and Nabais, 2015; Taib et al., 2020). In Europe, land-use changes and rural abandonment have led to both colonization by competing species such as oaks (Quercus rotundifolia, Quercus faginea) and pines (Pinus halepensis, Pinus sylvestris) and some local expansion into abandoned fields (Jiménez et al., 2003; Taib et al., 2020).

Management

Conservation of Spanish juniper requires protecting existing stands and enhancing regeneration in degraded areas through measures that reduce grazing pressure and allow organic matter accumulation beneath tree crowns, which supports seedling establishment (Taib et al., 2020). Restoration efforts should prioritize maintaining female trees, which are critical for recruitment success (Jiménez et al., 2003). Marginal and genetically isolated populations in Algeria may need assisted gene flow or reintroduction to prevent loss of adaptive diversity under climate change. In the Iberian Peninsula, managing interspecific competition and preserving open juniper woodlands are key to sustaining the species’ genetic and ecological resilience (Jiménez et al., 2003; Taib et al., 2020).

The bibliographic review was conducted by James Chaplin of the EUFORGEN Secretariat in August 2025.

Juniperus thurifera
Spanish juniper

Environmental zones

Genetic summary

Genetic diversity and variation

Genetic distribution and clustering

Gene flow

Further relevant genetic traits

Interspecific taxa dynamics

Glacial biogeography evolution

Genetic conservation

Threats

Management

Further reading

References

Juniperus thuriferaSpanish juniper

Environmental zones

Genetic summary

Genetic diversity and variation

Genetic distribution and clustering

Gene flow

Further relevant genetic traits

Interspecific taxa dynamics

Glacial biogeography evolution

Genetic conservation

Threats

Management

Further reading

References

Juniperus thurifera
Spanish juniper