|Scientific Name:||Diplotaxis siettiana|
|Taxonomic Notes:||Diplotaxis siettiana Maire is a wild relative of brassica crops as well as being related to cultivated perennial wall rocket, D. tenuifolia (L.) DC.|
|Red List Category & Criteria:||Critically Endangered B1ab(iii)c(iv)+2ab(iii)c(iv) ver 3.1|
|Assessor/s:||Pérez Latorre, A.V., Cabezudo, B., Mota Poveda, J., Peñas, J. & Navas, P.|
|Reviewer/s:||Bilz, M., Kell, S.P. & Nieto, A.|
|Contributor/s:||Gomez-Campo, C., Moreno Saiz, J.C., Mota Poveda, J., Nieto, A. & Kell, S.P.|
Diplotaxis siettiana is assessed as Critically Endangered because its extent of occurrence (EOO) is 0.0712 km² and its area of occupancy (AOO) is less than 2 km². All the populations occur in one location and there is a continuing decline in the quality and extent of is habitat and in the number of subpopulations. This species has been reintroduced into the island after observing a 90% population reduction in the 1980s.
The plant grows in a very small area and population numbers fluctuate greatly (principally due to human causes). Irrigation of the area with sea water where the plant was originally found, in order to reduce dust for helicopter landings, was the direct cause of extinction of this species. The island's fragile habitat has been largely modified by humans who recently introduced some domestic animals, causing further soil erosion and nitrification. Germination, flowering and fruiting are dependent on rainfall. An observation in 1970 referred to possibly hundreds of adult individuals, although only 150 were recorded in 1974, and none afterwards. In 1999, 48 plants were re-introduced but scientists are not sure that the population is self-sustaining. No dispersal to other parts of the island has taken place.
Diplotaxis siettiana is endemic to the Spanish island of Alborán (Almeria). This species was last seen in 1974, when seeds were fortunately collected before the species disappeared from the island. A reintroduction in 1999 appears to have been successful, although given extreme population fluctuations each year, more time is needed to ensure that the reintroduced population is self-sustaining. For the moment, it is believed to be possibly extinct in the wild.
Alborán is the top of a volcanic platform situated between Spain and Morocco, around 50 km from the nearest continent. This small island (600 m x 200 m) resembles an aircraft carrier due to its flat surface, reaching 10 m above sea level and surrounded by steep, almost vertical cliffs. The island has a lighthouse and is now used as a military base. In 1974 the plant was found growing in a tiny area around the helicopter platform. The area of occupancy (AOO) is less than 2 km² and the extent of occurrence (EOO) is 0.0712 km² which is the size of the island.
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||The number of individuals observed has varied from year to year, but it has never been less than 300. In 2000 there were more than 1,200 individuals and in 2003 there were 600. Those observations are the result of reintroductions of the species in 1999. The area of real occupation is less than 0.003 km².|
|Habitat and Ecology:||
The weedy nature of D. siettiana (it is an annual herb) makes it fairly tolerant to human disturbance. In fact it does grow in the more stable vegetation dominated by Frankenia pulverulenta and Mesembryanthemum nodiflorum, both apparently tolerant to high concentrations of salt and/or nitrogen. Rainfall is very low, with less than 100 mm per year.
This species is the only representative of the mustard family in the poor flora of Alborán (10 species). The island has long been inhabited, first by lighthouse keepers and later by the military which built the helicopter platform, widened the former small harbour, and constructed some temporary dwellings near the lighthouse.
The island is also of global importance as one of the few breeding sites for the threatened Audouin's Gull.
|Major Threat(s):||The island's very fragile habitat has been completely modified by humans, who introduced domestic cattle to the island, causing soil erosion and nitrification, and even irrigated the area in which the plant was found with salt water to reduce dust to facilitate the landing of helicopters (which may have been a direct cause for the extinction of this species). The construction of a new harbour can destroy the natural ecosystem of the island.|
This species is protected at the regional and European level. It is listed as a priority species in Annexes II and IV of the EU Habitats Directive and under Appendix I of the Convention on the Conservation of European Wildlife and Natural Habitats (Bern Convention). It is classed as Critically Endangered A1abc; B1ab(iii,v)+2ab(iii,v) in the Spanish national red list (Moreno 2008). The genus Diplotaxis is listed in Annex I of the International Treaty on Plant Genetic Resources for Food and Agriculture as part of the brassica complex.
The islet has been declared a Maritime-Terrestrial Reserve and Natural Place Paraje Natural by the Andalusian government, and has been nominated for the European Natura 2000 Network as SCI. Various reintroduction and re-enforcement campaigns were carried out in 1988 and 1999 to present.
Fortunately, before its extinction, some seeds had been collected and multiplied at the seed bank of the Agronomists College (Escuela de Agrónomos) of Madrid. When cultivated in botanic gardens (Jardín Botánico de Córdoba, Conservatoire Botanique de Brest), high germination rates can be achieved.
EURISCO reports only two germplasm accessions of D. siettiana held in European genebanks; however, only one originates from within Europe (Spain). This accession is stored in the genebank of the Escuela Técnica Superior de Ingenieros Agrónomos, Universidad Politécnica de Madrid (EURISCO Catalogue 2010). Germplasm collection and duplicated ex situ storage is a priority for this species.
This species should be added to the Spanish National Catalogue of Threatened Species, listed in the highest category (Endangered). Ideally the island should be designated as a strict Nature Reserve. If this is impossible, habitat restoration and on-going management still needs to be carried out indefinitely, including alien species eradication, monitoring, and no new construction of infrastructure. Periodic reinforcement campaigns in order to maintain the population might be necessary. The fact that D. siettiana seems to prefer semi-disturbed habitat and competes poorly with dominant species must always be taken into account.
|Citation:||Pérez Latorre, A.V., Cabezudo, B., Mota Poveda, J., Peñas, J. & Navas, P. 2011. Diplotaxis siettiana. In: IUCN 2013. IUCN Red List of Threatened Species. Version 2013.2. <www.iucnredlist.org>. Downloaded on 10 December 2013.|
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