Tetraclinis articulata (Vahl) Mast.

Thuja articulata Vahl, Callitris articulata (Vahl) Link, C. quadrivalvis Vent.

Habitat:

In very diverse substrates, in warm and dry terrains from semiarid to subhumid character, from the coastal plains to mountain ranges of the interior, where it reaches 1800 m. In certain regions this tree forms extensive forests, ± pure. Sometimes it grows in mixed forests, especially with Olea europaea, Pinus halepensis and, in SW Morocco, also with Argania spinosa.

Distribution:

It is essentially a North African species, although small relict populations survive in Malta and in the S of the Iberian Peninsula (Sierras de Cartagena and La Unión, Murcia, and possibly in other areas of Málaga and Huelva). In North Africa it grows in Morocco (in almost the whole country with the exception of the eastern plains and plateaux, the Saharan Atlas and other Saharan areas) and in NW Algeria (Tellian Atlas). Also frequent in NE Tunisia. It has been cited in Cyrenaica (NE Libya) and the central Sahara, but nowadays there are no known living specimens in any of these regions. About its presence in Cyrenaica, Durand and Barratte (1910), indicated in their Florae libycae prodromus, that the citations from the XIX century by Della Cella (1817) and Pacho (1825) could be due to a confusion with Cupressus sempervirens. This is also mentioned by Pampanini (1930) in his Prodromo della flora cirenaica. But for anyone who knows the Mediterranean flora, these two species are difficult to get confused since their leaves and fruits are quite different. Its long established presence in this area could also be confirmed by historic citations of T. articulata by Teofrasto c. 300 BC (Historia Plantarum V) when speaking about the best specimens: “…they are found around the temple of Hammon, but also grow in the interior of Cyrenaica.”

Observations:

It is a very primitive species with ancestors dating back to the early Tertiary, as T. brachyodon (Brongniart) Mai & Walther and T. salicornioides (Unger) Kvacek, widely distributed in what is now Europe and North Africa. However, despite the broad distribution of the genus during the Tertiary, the harsh climatic conditions of the Quaternary almost annihilated these species. In North Africa, due to its favourable climatic conditions, T. articulata evolved from its tertiary ancestors, forming large forests. Meanwhile, in the S of Europe, in protohistoric and historic times, this surviving species has been almost completely eliminated by man.

This slow growing small tree can live almost 500 years and reach a considerable size. In addition to its great scientific and biogeographical interest, the forests of this species play a vital role in stabilising soils in semiarid regions, which are currently threatened by erosion.

The thuja is a curious conifer for its peculiarity of regrowing again and again from the stump when the aerial part has been cut down. This, coupled with the rapid cicatrization of its wounds, allows this species to survive human exploitation better than other gymnosperm forests. This is the key to success of this primitive species allowing it to form large forests to this date. However, like all forests, if exploitation is too intense and continuous, these forests will eventually disappear.

The North African forests are, in general, heliophilous forestry formations, sometimes very large (thousands of hectares), but less and less dense, mainly due to repeated fires, overgrazing, the lifting of their stumps (for the value of its timber) and continuous soil erosion and consequent desertification. Other uses of its wood, which are quite destructive, consist of the extraction and burning of roots, trunks and branches, in artisan ovens on the ground, to obtain a type of turpentine similar to juniper oil. Its most used European name is “tar” and in Morocco is known as “gatran” or “gatran el ghalid”. With information gathered by Julin (2008), Charco (2017) has estimated that in a single Moroccan locality about 45,500 litres are obtained yearly, for which it is necessary to burn about 303,000 kg of roots, trunks and branches per year, mainly junipers and thuyas.

In North Africa there are 4,000,000 ha of mature thuja forest, according to data for Morocco provided by Emberger (1939), figure that was reduced to 2,500,000 ha by Boudy about ten years later. In any case it could be around 3,000,000 ha, of which there are currently only about 670,000 ha remaining. Morocco is currently the country with the largest thuja forest expansion, where the climax area was estimated by the cited authors to have occupied between 3,700,000 and 1,860,000 ha, of which 566,000 ha remain today (Haut Commissariat aux Eaux et Forêts et à la Lutte Contre la Désertification, 2016). That is to say, more than 1,000,000 ha of a well adapted tree have been lost to human aggression. A tree that regrows easily and heals quickly after fires and mutilations and also grows on land unsuitable for agriculture, which gives an idea of the magnitude and intensity of the continuous deforestation in this country. The situation is not much better elsewhere. In Algeria the climax area has been estimated at 521,000 ha, of which still about 72,300 ha remain, according to the national report of the Institut National de Recherche Forestière for FAO (2012). In Tunisia, however, the natural area of the thuja (about 25,000 ha) has seen little reduction, it even seems to have increased noticeably: 30,438 ha, according to its Direction Générale des Forêts.

Conservation status:

In the IUCN Red List of Threatened Species it is listed at a global level as Least Concern (LC) (Sánchez Gómez et al., 2011). However, because there is a strong decline of the Moroccan populations, if assessed at a regional and/or national level, it would probably be assessed under a threat category. In Algeria it is included in the List of protected non cultivated flora (Executive Decree 12-03 on 4-Jan-2012).