Juniperus thurifera (Spanish juniper) description

(subsp. thurifera)
Conservation status
(African subspecies)

Juniperus thurifera

Common names

Incense juniper, genévrier thurifère; cedro de España, trabina, sabina blanca, enebro, aoual, taoualt, araar, Spanish juniper. Subsp. africana is Atlas juniper and subsp. aurasiaca is Algerian juniper.

Taxonomic notes

Three subspecies:

Juniperus thurifera L. subsp. thurifera. Type: Spain: Aragon: Teruel ("Mansana, Camarena"), E. Reverchon 788 (neotype BM). See Farjon (2005) regarding the neotype. See POWO for synonymy. Native to France and Spain.
Juniperus thurifera subsp. africana (Maire) Gauquelin, Idr.Hass. & P.Lebreton (1988). Lectotype: Morocco, Grand Atlas, Ourika, montagne gréseuse au-dessus d’Anfegueïn, 2400 m, 9 juillet 1921, Dr R. Maire, MPU005212 (Véla and Schäfer 2013). See POWO for synonymy. Native to Morocco.
Juniperus thurifera subsp. aurasiaca (Véla & P.Schäf.) Véla (2018). Type: Algeria, Aures, cedar groves in Sgag, on marl and limestone, 1600-1800 m elevation, 1920.07.02, female, René Maire s.n., MPU005199 (Véla and Schäfer 2013). See POWO for synonymy. Native to Algeria.

There are two named hybrids, reported from the province of Castellon in Spain. Juniperus × palanciana J.M.Aparicio & Uribe-Ech. is the hybrid of J. phoenicea and J. thurifera (Rojo and Uribe-Echebarría 2008), and Juniperus × cerropastorensis J.M.Aparicio & Uribe-Ech. is the hybrid of J. sabina and J. thurifera (Rojo and Uribe-Echebarría 2009). Both are unusual instances of a diploid crossing with J. thurifera, a tetraploid. Also, J. sabina var. balkanensis is distinguished from other J. sabina in having the chloroplast genome of J. thurifera (Adams et al. 2016). For further discussion of these hybrids see Farhat et al. (2020).

This species was long recognized as a distinctive Mediterranean juniper, and is clearly a member of the smooth-leaf-margin clade of Eastern hemisphere junipers, section Sabina. Recent molecular and morphological analyses place it within a subclade that includes J. foetidissima and the J. excelsa-J. polycarpos-J. seravschanica complex, distributed from the eastern Mediterranean to northernmost India (Marcysiak et al. 2007, Adams and Schwarzbach 2013). J. thurifera differs from its sister species in being one of the few tetraploid junipers (Farhat et al. 2019). Identification of the infraspecific taxa was a more complicated process, and into the 21st century some authors were reducing them all to synonymy on the basis of overlapping morphologies (e.g., Farjon 2010). However, Maire (1926) early recognized the North African plants as distinctive on the basis of morphological characters, and this was confirmed much later by nucleic acid and chemotaxonomic studies that revealed clear biogeographic patterns within the species (Achak et al. 2006, 2009; Adams et al. 2001, 2003; Akkad et al. 2001; Gauquelin et al. 1988; Romo et al. 2013; Taib et al. 2020; Texeira et al. 2014); subsequent detailed studies also demonstrated biogeographic separation, reproductive isolation, and consistent morphological differences between the three subspecies, warranting distinction at subspecies rank (Boratyński et al. 2013, Gauquelin et al. 1988, Marcysiak et al. 2007; Romo and Boratyński 2005, 2007; Terrab et al. 2008; Vela and Schäfer 2013). Somewhat surprisingly, the most detailed genetic analysis to date indicates greater affinities between the Algerian and European populations than between the Algerian and Moroccan populations (Taib et al. 2020), likely indicating dispersal events from Europe to Algeria (Terrab et al. 2008). There have also been chemotaxonomic varieties described within the European subspecies (Gauquelin et al. 1988), but these are not widely recognized.

Description

Dioecious evergreen shrubs, or trees up to 20 m tall and 200 cm dbh. Crown pyramidal in youth, later becoming broad, rounded, often irregular. Trunks single or multiple, often branching near the ground. Bark thin, dark brown, with age weathering gray-brown, becoming scaly, and exfoliating in strips. Structural branches dense, spreading or ascending. Foliage branches spreading or drooping, branchlets 1-1.3 mm thick, more or less quadrangular, covered with scale leaves in 4 highest orders of branching, persistent. Leaves light green, decussate, imbricate, decurrent, scale leaves on ultimate branchlets all appressed, on ultimate branchlets 1.3-2.7 × 0.7-1 mm, ovate-rhombic, margins entire or hyaline-erose. Scale leaves on older branchlets and whip shoots larger, to 8-10 × 2.5 mm, lanceolate, apiculate, abaxial stomata in two small areas near the base, adaxial stomata in two bands converging to the apex, gland central but usually inactive, in slight depression. Pollen cones terminal, solitary, subglobose, 2-3 mm long, yellow-green maturing to light brown; microsporophylls 10-12. Seed cones terminal, growing in two seasons, consisting of 2-3 pairs of spreading but incurved bracts fusing to form a subglobose cone 7-8(-10) mm diam., black-blue or purple-black at maturity. Seeds (1-)2-3 per cone, irregular in size and shape in a single cone, 3-5 x 3-4.5 mm, triangular or flattened, with shallow pits and grooves, lustrous light brown, with a dull tan hilum at base. Cotyledons 2, 20-30 × 3-4 mm. Juvenile leaves on seedlings and reappearing on mature plants, in whorls of 4 on lower stem, on branchlets decussate, acicular, 3-6 mm long with a green adaxial midrib, acute-pungent (Farjon 2005). See García Esteban et al. (2004) for a detailed characterization of the wood anatomy.

The morphological differences between subspecies are almost inconsequential; they can be demonstrated by measuring statistically significant numbers of specimens, but a single plant occurring outside its native habitat could not be identified solely on the basis of morphology. The only consistent described differences are in the diameter of mature seed cones as measured on (dried) herbarium specimens: 4.5-8.5 mm in subsp. africana, 5-9.5 mm in subsp. aurasiaca, and 6.5-10.5 mm in subsp. thurifera (Véla and Schäfer 2013). Also, the African subspecies generally have 1 seed per cone, vs. 2 (rarely 3) seeds in subsp. thurifera (Adams 2014).

Distribution and Ecology

France, Spain, Morocco, and Algeria, but with a highly fragmented distribution confined largely to mountains at 300-3300 m elevation. In Spain it is widely distributed, mostly on carbonate substrates, mainly in mountains from Andalusia to the Pyrenees but also as an early-successional species in lower elevation areas such as abandoned pastures and farmland (De Soto et al. 2010). It occurs with J. oxycedrus and various species of oaks. In France it is local in the Pyrenees and the French Alps, and also in Corsica. In Morocco it occurs at 1700-3400 m elevation in the Atlas and Anti-Atlas Mountains with an extent of ca. 300 km²; it is on varied substrate but seems to be most abundant on carbonates (Romo and Boratyński 2005). In Algeria it is confined to the Aurès Mountains. Habitat suitability modeling confirms north-central Spain and the high Atlas as having the highest suitability for this species, and in fact these are the areas where it is most abundant (Taib et al. 2020). Throughout its range the climate is continental, semiarid, with generally cold winters (due to high elevation) and long dry summers (Farjon 2005). Habitat modeling indicates the climate factors most strongly limiting the species' occurrence are mean temperature of the coldest quarter, minimum temperature of the coldest month, mean temperature of the driest quarter, and precipitation of the warmest quarter (Taib et al. 2020). The same study also identified some substantial differences in climatic conditions and limits between the European and African populations, which further supports their assignment to different subspecies. Smaller but measurable differences separate the Moroccan and Algerian populations. Hardy to Zone 8 (cold hardiness limit between -12.1°C and -6.7°C) (Bannister and Neuner 2001).

See Montes and Bertaudiere (2005) for details, a map, and photos showing habitat; see Romo and Boratyński (2005) for similar discussion of the Morocco populations. In the Aurès Mountains it is the only tree species at the upper tree line (about 2500 m elevation, with isolated specimens found above 3000 m). At the lowest altitudes, Quercus ilex is generally associated with J. thurifera. In the Middle Atlas mountains, J. thurifera is often associated with Cedrus atlantica (Nicolas Montes email 1998.03.05).

Like most junipers, the seeds are dispersed by animals, including birds and livestock; both are highly effective vectors in semiarid lands. The foliage is eaten by sheep (R.M. Clegg email 2009.02.20). A study in Spain (Santos and Tellería 1994) found that in large, continuous patches of woodland, the most effective seed dispersers were thrushes (Turdus spp.), whereas in small, discontinuous patches most seeds were consumed by mice (Apodemus sylvaticus), suggesting that forest fragmentation may be contributing directly to reduced reproductive success in J. thurifera.

Conservation status: In Spain, the species is generally widespread with stable population trends, which is consistent with the "Least Vulnerable" conservation rating assigned by the IUCN. The species is rare in France and those populations are likely of conservation concern. In Morocco, heavy grazing and browsing pressures have caused damage to living trees and prevented regeneration (Gauquelin et al. 2000). The species has also long been gathered for firewood and has declined as a result of overexploitation due to logging and wood harvesting in the context of an increasing human population (Romo and Boratyński 2005). Also, "Overgrazing and branch cutting negatively affect the regeneration ability of this species, since the organic matter that accumulates beneath the trees’ crowns is the most suitable site for recruitment. A lack of such conditions hampers regeneration and leads to demographic collapse" (Taib et al. 2020 and sources therein). The situation is even more dire in Algeria, where the same pressures are affecting a much more restricted population of trees. "Currently, all Algerian stands suffer from a lack of natural regeneration, and old individuals prevail in most of the populations, which probably also decreases their reproductive abilities. Generally, thuriferous juniper in Algeria produces seeds sporadically, and most of them are empty" (Taib et al. 2020). Besides these issues, climate change forecasts indicate some rangewide declines in habitat suitability during the remainder of the 21st century (Taib et al. 2020).

Remarkable Specimens

The largest tree on record is an individual 19 m tall with a girth (due to its multistemmed form) of 16 m, located in the Middle Atlas, near the "Col du Zad," about 50km N of Ifrane (Nicolas Montes email 1998.03.05).

Ongoing dendrochronological research (Montes and Bertaudiere 2005) has not yet established precise ages, but the maximum is probably more than 500 years (Nicolas Montes email 1998.03.05). Rozas et al. (2009), studying trees in north-central Spain, identified individuals up to about 340 years old, crossdated age.

Ethnobotany

In France and Spain, J. thurifera was traditionally used for construction, firewood and special uses such as fencing and tools. The foliage served as fodder for donkeys and goats. These types of use are still prevalent in North Africa (Farjon 2005). See also remarks in Montes and Bertaudiere (2005).

The species has seen limited use in dendrochronology, including demographic and climatological studies in both Spain and Morocco (Rozas et al. 2009, De Soto et al. 2014, Fuster et al. 2020).

Observations

Montes and Bertaudiere (2005) provide clues on where to find native specimens. Several stands occur in the High and Middle Atlas mountains (Nicolas Montes email 1998.03.05).

Remarks

The epithet is from the Latin turifer, "producer of incense".

A variety of studies of J. thurifera have revealed some unexpected consequences of dioecy in junipers. Studies in both the Atlas Mountains of Morocco and the Pyrenees of Spain have found a preponderance of female trees (Gauquelin et al. 2002). An experimental study found that male plants had lower gas exchange rates and radial growth but greater reproductive investment and higher water use efficiency than female plants. Supplemental fertilization resulted in increased photosynthesis rates in in males but not in females, which had consistently high photosynthetic rates regardless of experimental treatments. These results show that male and female plants invest surplus nitrogen in different ways, with females increasing nitrogen storage to compensate for high expenditures in seed crop production, while males are reactive to relatively short-term variations in nutrient availability (Montesinos et al. 2012). A dendrochronological study in central Spain found that young female trees showed highest sensitivity to summer water stress, compared to male or older trees; this in turn suggests lower water use efficiency in female trees (Rozas et al. 2009). Similarly, on relatively productive sites, females grow more and store more non-soluble sugars (i.e., carbohydrate reserves) than males (DeSoto et al. 2016); presumably this strategy allows the females to "save" carbohydrates for use in subsequent seed cone production.

Citations

Achak, Nadia, Abderrahmane Romane, Mohamed Alifriqui, and Robert P. Adams. 2006. Effect of the leaf drying and geographic sources on the essential oil composition of Juniperus thurifera L. var. africana Maire from the Tensift - Al Haouz, Marrakech region. Journal of Essential Oil Research 20:200-204.

Achak, Nadia, Abderrahmane Romane, Mohamed Alifriqui, and Robert P. Adams. 2009. Chemical studies of leaf essential oils of three species of Juniperus from Tensift Al Haouz-Marrakech region (Morocco). Journal of Essential Oil Research 21: 337–341.

Adams, Robert P. 2014. Junipers of the World: The Genus Juniperus. Fourth edition. Trafford Publishing. Brief versions of the descriptions are available online at Adam's website, www.juniperus.org.

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Adams, Robert P., Luke E. Mumba, Shelley A. James, Ram Naresh Pandey, Thierry Gauquelin, and Wadi Badri. 2003. Geographic variation in the leaf oils and DNA fingerprints (RAPDs) of Juniperus thurifera L. from Morocco and Europe. Journal of Essential Oil Research 15:148–154.

Adams, Robert P., Andrea E. Schwarzbach, and Alexander N. Tashev. 2016. Chloroplast capture in Juniperus sabina var. balkanensis R. P. Adams and A. N. Tashev, from the Balkan peninsula: A new variety with a history of hybridization with J. thurifera. Phytologia 98(2):100–108.

Akkad, S., F. Akssira, F. Mellouki, A. F. Barrero, J. Quilez del Moral, P. Arteaga, M. M. Herrador, and A. Belgarrab. 2001. Étude de la composition des huiles de Juniperus thurifera L. var. africana a l’aide du couplage CG-MS. 2ème Colloque International: Le genévrier thurifère et les forêts d’altitude dans les montagnes du partout méditerranéen. Marrakech, avril 2001. Livre des résumés.

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