Habitat, occurrence and conservation of Saharo-Arabian-Turanian ...

Journal of Arid Environments (2003) 53: 491–500
doi:10.1006/jare.2002.1062
Habitat, occurrence and conservation of
Saharo-Arabian-Turanian element Forsskaolea
tenacissima L. in the Iberian Peninsula
Javier Cabello*, Domingo Alcaraz, Francisco Gómez-Mercado,
Juan F. Mota, Javier Navarro, Julio Peñas & Esther Giménez
*Departamento de Biología Vegetal y Ecología. Universidad de Almería,
E-04120 Almería, Spain
(Received 30 January 2002, accepted 11 June 2002)
The aim of this study is to assess the Iberian populations of Forsskaolea
tenacissima L. according to its biogeographical interest, habitat, geographical
range and conservation status. Results point out that they are restricted to
gravel wadis of Tabernas Desert (SE Spain), are scarcely included in
protected areas and represent historically isolated populations with relict
behaviour. We also describe a new association, Senecioni-Forsskaoleetum
tenacissimae. Conservation status of species is cause for concern and two
conservation actions must be carried out. Firstly, protected areas should
house Forsskaolea populations and secondly, phytosociological characterization
of a community allows inventorying its habitat and directing conservation
efforts to community level.
# 2002 Elsevier Science Ltd.
Keywords: biodiversity; flora; phytosociology; protected areas; reduced
geographical range; relict populations; semi-arid ecosystems; Tabernas Desert
Introduction
The origin of the steppe areas in the Iberian Peninsula along the Pleistocene is an old
classic controversial issue. The so-called ‘Steppe Theory’ (Del Villar, 1915)
considered the vegetation of these ecosystems as the result of the destruction of
primitive sclerophilous forests. For this reason the flora and vegetation of these
ecosystems have been undervalued for conservation priorities. However, the most
recent trend is to consider the possibility of persistence of non-forested areas across
the Pleistocene in the Iberian Peninsula (e.g. Terradas, 1986; González-Bernáldez,
1989; Suárez Cardona et al., 1992; Blondel & Vigne, 1993; Suc et al., 1995; Willis,
1996; Ribera & Blasco-Zumeta, 1998).
This debate is important because as Gómez-Campo (1985) pointed out, the origin
of Mediterranean flora has deep implications with regard to conservation attitudes. In
SE Spain, steppe areas are semi-arid ecosystems that support a notable richness in
*Corresponding author. Fax: +34-950-015-069. E-mail: jcabello@ual.es
0140-1963/03/040491 + 10 $30.00/0 # 2002 Elsevier Science Ltd.

492 J. CABELLO ET AL.
species, with a large number of endemisms and Mesogean elements (Peinado et al.,
1992; Cabello, 1997). One of the latest is the Saharo-Arabian–Turanian element
Forsskaolea tenacissima L. (Danin & Orshan, 1999) extending into the Mediterranean
region (Fig. 1). This plant has a disperse geographical distribution along Palestine
(Zohary, 1966; Evenari et al., 1971), Egypt (Ayyard & Ghabbour, 1986), North Africa
and Sahara Desert (Ozenda, 1983; Le Houérou, 1986, 1995) and SE Spain (Sagredo,
1987; Paiva, 1993).
Literature (Sagredo, 1987; Paiva, 1993; Lorite et al., 1998), suggests that the
geographical range in Europe of this species is restricted to a few localities in SE
Iberian Peninsula, where the regional climate is notably semi-arid both due to the
rainfall shadow effect of the main Betic ranges and its proximity to northern Africa
(Geiger, 1973).
Regarding the biogeographical and ecological interest of this species in a European
biodiversity scenario, the aim of this study is to assess the populations of F. tenacissima
L. in the Iberian Peninsula according to its habitat, geographical range and
conservation status. Taking into account that conservation becomes more logical
when directed to syntaxa or to ecosystems than to a single species (Gómez-Campo,
1985), we studied the habitat of the species to enhance its role as a conservation
target.
Material and methods
The study was based on collections, literature and fieldwork carried out during
1999–2000. To assess the habitat of the species we studied biotope, community
and bioclimatic traits. At the community level we studied the phytosociological
behaviour of the species according to the Zurich–Montpellier school methods
(Braun-Blanquet, 1979; Gehú & Rivas-Martínez, 1981). Taxa nomenclature first
follows Castroviejo et al. (1986–2001) and Tutin et al. (1964–1980) for those
taxa non-cited in the former reference. The syntaxonomical scheme follows
Rivas-Martínez et al. (2001). For the description of this new association we
used International Code of Phytosociological Nomenclature (Weber et al., 2000).
For bioclimatic characterization of the populations, we considered bioclimatic
It index proposed by Rivas-Martínez & Loidi (1999). Conservation
status was studied to assess the occurrence of populations in protected areas
(Fig. 2).
Results
Geographical range
Iberian populations are restricted to gravel banks of some wadis of Tabernas Desert
(Fig. 2): Rambla de Espinaza (Losa & Rivas Goday, 1968), Rambla de San Indalecio,
Rambla de Gérgal (Kunkel, 1987), Rambla de Tabernas (Kunkel, 1987; Sagredo,
1987), Rambla de los Yesos (Lorite et al., 1998). As a result of fieldwork we confirmed
all citations, and we added new localities: Rambla de San Telmo (Herbario de la
Universidad de Almería, 1317) y Rambla de Los Alhamillos-Gérgal (Herbario de la
Universidad de Almería, 1318).
Habitat
Iberian populations inhabit on gravel banks. This biotope emerges naturally in
wadis, and in man-made terraces in flood plains of Tabernas Desert. Considering

ASSESSMENT OF IBERIAN POPULATIONS OF FORSSKAOLEA TENACISSIMA 493
Figure 1. Geographical range of Forsskaolea tenacissima L. in the Mediterranean Basin and bioclimatic features of its area.

494 J. CABELLO ET AL.
Sierra Nevada
Natural Park
Tabernas
Desert
Tabernas
Natural Park
2
1 3 6 5
4 7
8
9
10
ATLANTIC
OCEAN
Sierra Alhamilla
Natural Park
N
Iberian
Peninsula
Morocco
Almería
MEDITER-
RANEAN
SEA
Algeria
MEDITERRANEAN
SEA
0 10
km
Figure 2. Location of Forsskaolea tenacissima L. populations in the Iberian Peninsula. (1)
Rambla de Los Yesos; (2) Rambla de Los Alhamillos-Gérgal; (3,4) Rambla de Gérgal; (5–7)
Rambla de Tabernas; (8) Rambla Espinaza; (9) Rambla de San Indalecio; (10) Rambla de San
Telmo.
the species composition recorded in the relevés, the community of F. tenacissima
(Table 1) belongs to Glaucion flavi Alliance (Andryaletalia ragusinae Order, Thlaspietea
rotundifolii Class), which represent the vegetation of gravel and pebbles of riverbanks
in the Mediterranean Region. The community always appears in the early stages
of succession, and when the substratum becomes steadier, perennial communities of
Pegano-Salsoletea Class displace it. Due to this, on the bank of the wadis, where
the disturbances more frequently occur in a natural way, the community is more
constant.
Forsskaolea tenacissima populations appear from 100 to 500 m of altitude. The
aridity of its distribution area is obvious since the annual rainfall average is lower than
300 mm, and recent studies of Tabernas Desert reveal that 34% of the months it is
lower than 10 mm (Lázaro et al., 2001). According to the bioclimatological indices
from Rivas-Martínez & Loidi (1999), the geographical range falls in the Mediterranean
desertic–oceanic bioclime, thermo-Mediterranean arid and semi-arid belts
(Table 2).
Conservation status
The area of occupancy is extremely reduced, since we only found seven main
populations (Table 2), which are scarcely included in protected areas. Only the
Rambla de Tabernas population is partially embraced by the Tabernas Desert Natural

ASSESSMENT OF IBERIAN POPULATIONS OF FORSSKAOLEA TENACISSIMA 495
Table 1. Senecioni flavi–Forsskaoleetum tenacissimae ass. nov.
1 2 3 4 5 6 7 8 9 10
Altitude (m) 228 198 300 300 325 325 325 255 100 300
Exposure E F E E E E E F F SW
Slope (1) 40 F 25 40 20 15 15 F F 20
Area (m 2 ) 25 25 25 30 25 25 20 25 20 20
Association and higher
syntaxa features
Forsskaolea tenacissima 2 2 2 2 2 2 + 2 2 2
Senecio flavus . 1 + 1 1 + 2 . 1 2
Andryala ragusina 2 2 1 2 1 2 . 1 1 .
Ononis talaverae + . . + . . . + + .
Scrophularia canina + . . . . . . 1 . .
Lactuca viminea . . . . . . . + . .
Accompanying species
Launaea arborescens 2 + + + 1 + + 1 + 1
Reseda lanceolata + . 1 1 + + 1 . 1 1
Glaucium flavum . . 1 1 + 1 + . + +
Genista umbellata . + 1 . . + + . + +
Diplotaxis harra subsp. 1 . . + + + 1 . . 1
lagascana
Anthyllis cytisoides + . . + . + . 1 . +
Dittrichia viscosa . . + . 1 1 . . . +
Dorycnium pentaphyllum + . . . 1 . . 1 . .
Limonium insigne . . + . + . . . . .
Anthyllis terniflora . . . . + . . 1 . .
Lavandula multifida . . . . + . . 1 . .
Fagonia cretica . . . . . . . . + +
In addition: Asphodelus albus +, Atriplex halimus +, Sonchus tenerrimus +, Launaea fragilis 1en1.Eryngium
campestre +en2.Salsola kali +en4.Centaurea melitensis +, Salsola genistoides + en 5. Bituminaria
bituminosa +, Atriplex glauca +en6.Piptatherum miliaceum 1, Zygophyllum fabago +, Corrigiola telephiifolia
+, Launaea lanifera +, Retama sphaerocarpa +, Artemisia barrelieri +, Frankenia corymbosa +, Thymelaea
hirsuta +en8.Glaucium corniculatum +, Euzomodendron bourgaeanum +, Anabasis articulata +en9.
Herniaria fontanesii subsp. almeriana + en 10.
Localities (all of them in Almería Province, Spain): 1 Rambla de Tabernas WF4795; 2. Rambla de
Tabernas WF4793; 3–7, Rambla de Tabernas WF4895; 8, Rambla de Gérgal WF4093; 9, Rambla de San
Indalecio WF5185; 10, Rambla de Espinaza WF5389.
Park and the Rambla de Los Yesos population is included in the Sierra Nevada
Natural Park. The rest of them are outside any protected area (Fig. 2).
Discussion
The ecological behaviour described above for Iberian populations of F. tenacissimae
agree with other world areas. Gravel banks of Tabernas wadis represent the same
edaphic conditions described for other areas like the Negev Desert (Evenari et al.,
1971) or the Sahara Desert (Maire, 1952–1977). The Tabernas Desert with
Mediterranean hyperdesertic and Mediterranean desertic–oceanic bioclimes (according
to Rivas-Martínez & Loidi, 1999), is the only European area with similar
bioclimatic conditions to semi-arid areas of North Africa and West Asia (Fig. 1).

Table 2. Location, bioclimatic traits and presence in protected areas of Iberian populations of Forsskaolea tenacissima L.
Localities Population Geographic
coordinates (UTM)
Bioclimatic traits
Alt* (m) It w Pp z (mm)
Protected area
Rambla de Los Yesos 1 30SWF3199 500 340 340 Sierra Nevada Natural Park
Rambla de Los
2 30SWF4199 300 300 290 F
Alhamillos-Gérgal
Rambla de Gérgal 3
4
Rambla de Tabernas 5
6
7
30SWF4093
30SWF4092
30SWF4895
30SWF4795
30SWF4793
220
260
250
190
200
295
300
300
290
290
271
280
279
263
279
F
Tabernas Desert Natural Park
(Partially)
Rambla de Espinaza 8 30SWF5389 250 300 279 F
Rambla de San
9 30SWF5086 150 280 252 F
Indalecio
Rambla de San Telmo 10 30SWF4576 100 275 240 F
*Altitude.
w It: Thermicity index: Sum, multiplied by 10, of the annual mean temperatures (T), mean maximum temperature of the coldest month (M) and mean minimum
temperatures of the coldest month (m), It = 10(T+M+m) (Rivas-Martínez & Loidi, 1999).
z Precipitation.
496 J. CABELLO ET AL.

ASSESSMENT OF IBERIAN POPULATIONS OF FORSSKAOLEA TENACISSIMA 497
Iberian F. tenacissima communities present biogeographical and floristic traits that allow
us to propose a new association. Thermo- and meso-Mediterranenan shrublands of stony
areas and dry rivers distributed throughout the East Iberian Peninsula and Balearic
Islands belongs to Andryaletum ragusinae association (G. flavi Alliance), led by Andryala
ragusina L. and Mercurialis tomentosa L. (Bolós, 1967). However, the community of the
Tabernas Desert wadis is led by both F. tenacissima and Senecio flavus (Decne.) Sch. Bip.
ThefirstoneisaSaharo-Arabian–TuranianelementandthesecondoneisaWest
Mediterranean element with restricted distribution in the Iberian Peninsula. From a
biogeographical standpoint and at regional scale, both elements are differential taxa from
the Occidental-Almerian District with regard to the rest of the Almerian SectorF
Murcian–Almerian Province (Peinado et al., 1992; Mota et al., 1997).
Because of this floristic feature and the frequent presence in the relevés of
Ononis talaverae, another restricted Iberian–North-African element (Devesa, 2000),
we described a new endemic association for the Occidental-Almerian District
(Almerian Sector, Murcian–Almerian Province) (Table 1, syntypus rel. 4). The
presence in the relevés ofSalsolo-Peganion elements as accompanying species is due to
the pioneer perennial vegetation which is the spatial and successional contiguous
vegetation.
Preservation of isolated populations and capturing the geographic range of species is
widely demanded in Conservation Biology (Rojas, 1992; Sutherland, 2000; Scott
et al., 2001). Reasons for this are the possible effects on biodiversity elements caused
by global and regional climate changes (Peters & Lovejoy, 1992), the need to maintain
genetic diversity (Jones et al., 2001), and the fact that stochastic events may threaten
resources restricted to just one area (Pressey et al., 1993, 1994). Moreover, Lesica &
Allendorf (1995) suggest that populations on the periphery of their ranges may be the
most genetically variable and thus evolutionarily valuable if they are confronted with
contracting ranges, and so may be less vulnerable to anthropogenic or natural
changes.
The main objective of this work was to assess F. tenacissima as a conservation
flora priority in the European context. Taking into account that the last connection
between Africa and Europe was 3 millions years ago (Sanz de Galdeano, 1997),
the Tabernas Desert populations represent historically (at geological-evolutionary
time scale) isolated populations from the rest of African, Arabian and Turanian
populations, and hence, as we showed above, they are interesting from biodiversity
point of view. In addition, its occurrence in the SE Iberian Peninsula has a
great importance from a biogeographical approach. This is due to two facts: on
the one hand, it reflects both the floristic interchange between SE Iberian Peninsula
and northern Africa and western Asia during the Messinian desiccation of
the Mediterranean Sea (Suárez et al., 1992), and, on the other one, it stresses
the hypothesis of considering the presence of steppe habitats along the Pleistocene in
the Iberian peninsula. Some authors suggest that those areas, less affected by glaciers,
constituted refuges for xerophytic elements during the Quaternary Period (Bolós,
1951; Blanca, 1991; Cabello, 1997).
Whereas in other areas such as Israel, it is a common taxon (The Hebrew University
Herbarium, 2000) in the Iberian area it is rare. Predictive distribution based on
bioclimatic and ecological conditions suggest that the species should appear in most of
the Murcian–Almerian Province. However, as a result of the fieldwork, even within the
Tabernas Desert, we have observed just a few populations. Two reasons for such a
restricted area of occupancy might be either a low dispersal capacity of F. tenacissima
or the fact that Tabernas basin materials are mainly Tortonian marine marls, and
hence many wadis have high salinity conditions. In addition, peripheral populations of
a given species tend to be smaller and more isolated than core populations. In any
case, the relict behaviour of Iberian populations is clearly stressed by their reduced
geographical range.

498 J. CABELLO ET AL.
According to the last Red List of Spanish Vascular Flora (VV.AA., 2000), F.
tenacissimae, with the IUCN threatened category VU D2, is facing a high risk
of extinction in the wild in the medium-term future. We believe that it is a cause
for concern that Iberian populations are scarcely included in protected areas.
Categorization of species according to their vulnerability to extinction in red lists
does not represent an effective measure to preserve biodiversity. Two conservation
actions could be carried out. At a local scale, present protected areas in
SE Iberian Peninsula must be reviewed, embracing Forsskaolea populations as
conservation targets. At a regional scale, the phytosociological characterization of
this new described community allows the inventory and incorporation of this biotope
in the European Communities CORINE information and Mapping System (EUR
12587, 1991), to be subsequently included in the EU Habitats Directive 92/43/EEC.
Syntaxonomic scheme
Class Thlaspietea rotundifolii Br.-Bl. 1948 + Order Andryaletalia ragusinae Rivas Goday
ex Rivas Goday & Esteve 1972. Alliance Glaucion flavi Br.-Bl. Ex Tchou 1948
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