Ecologia Mediterranea

N. BOUCHENEB, S.S. BENHOUHOU
72
rocky substrate with boulders and crevices,
for an altitude varying between 1380 and
1600 m. This association is characterised
physiognomically by Rhus tripartita (Ucria)
Grande and Olea europaea subsp. laperrinei
(Table 1).
On boulders, talus scree and crevices Olea
europaea subsp. laperrinei is dominant.
Species with an average frequency are all
chasmophiles belonging to the Aervo-Fagonion
Quézel 1965 (Aerva javanica (Burm. F.)
Juss. ex Schult., Aizoon canariense L., Anabasis
articulata (Forssk.) Moq., Fagonia
bruguieri DC., F. longispina Batt.,
Forsskaolea tenacissima L., Helianthemum
ruficomum (Viv.) Spreng.) and to the Acacio-
Panicion (Acacia ehrenbergiana Hayne,
Heliotropium bacciferum Forssk., Pulicaria
undulata (L.) C.A. Mey. Trichodesma
africanum (L.) R. Br.).
This association is close to the Olea europaea
subsp. laperrinei-Crambe kralikii Coss. association
described by Quézel (1965) at much
higher altitudes (1800 to 2400 m), which is
related to the Lavanduletea antineae Quézel
1965. The absence of characteristic species
belonging to the Lavanduletea antineae
Quézel 1965 such as Lavandula antineae,
Ballota hirsuta Benth., Erigeron trilobus
(Decne.) Boiss., Globularia alypum L.,
Hyparrhenia hirta (L.) Stapf and Crambe kralikii,
all high altitude species that first appear
at 1800 m, leads us to consider another syntaxonomical
hierarchy. When considering the
floristic list, our association is best related to
the Aervo-Fagonion, the Aervo-Fagonietalia
and the Asterisceto-Forsskaoletea Quézel
1965. The unique assemblage of chasmophiles,
confined to rocky terrain for altitudes
ranging between 1400 and 1600 m and
described for the first time in the north and
north-eastern regions of Tamanrasset is sufficiently
distinctive to require the definition of
a new association – one floristically characterised
by Rhus tripartita and Olea europaea
subsp. laperrinei.
The Cassia aschrek and Panicum
turgidum community
This association corresponds to the floristic
group E2 identified by the correspondence
analysis (Figure 4). It is represented by sixteen
relevés taken from wadi beds and nearby
terraces as well as from outwash zones. Soil
substrates varied from sandy-gravelly to
sandy-rocky textures. The altitude at which
the relevés were taken varied between 1000
and 1500 m. This association was observed in
wadi Taddadine, Ouezzene in the Ahléheg
massif, wadi Tit in the Ti-n-Tourdi massif,
wadi Tafirt in the Tahelgha massif and wadi
Tehart, in the Alemeda massif (Figure 3).
According to the physiognomically dominant
plants, this association corresponds to the
Acacia-Panicum desertic savannah first
described by Maire (1940). Vegetation is characterised
by the dominance of trees and
shrubs among which the most important ones
are Acacia ehrenbergiana, Acacia tortilis
subsp. raddiana (Savi) Brenan and Maerua
crassifolia Forssk. (Table 2).
Detailed analyses of the floristic composition
of this association showed that the characteristic
species belonging to the Acacio-Panicion
alliance, particularly Acacia ehrenbergiana,
Acacia tortilis subsp. raddiana and Zilla spinosa
(L.) Prantl, have high frequency scores.
Species characteristic of the Pergulario-Pulicarietea
Quézel 1965 are also well represented
with frequencies as high as IV. Characteristic
species of our association are the
same as those proposed by Quézel (1965) to
define the Cassia aschrek (Senna italica
Mill.) and Panicum turgidum Forssk. community.
Likewise characteristic species of the
Salvia chudaei Batt. & Trab. sub-association
are: Salvia chudaei, Artemisia campestris L.,
Deverra scoparia Coss. & Durieu subsp. scoparia
and Cymbopogon schoenanthus (L.)
Spreng. Considering the very close similarity
of the characteristic species for the different
units of the phytosociological framework
given for the Acacia-Panicum desertic savannah,
the vegetation type documented in
Table 2 corresponds to the association of Cassia
aschrek-Panicum turgidum Quézel 1965
and the Salvia chudaei sub-association. Field
observations showed that Deverra scoparia
subsp. scoparia has a much higher frequency
than Salvia chudaei, which strongly supports
proposing Deverra scoparia subsp. scoparia
to characterise the sub-association rather than
Salvia chudaei. The ecological optimum of
Deverra scoparia subsp. scoparia is around
1300 m and has also been observed in the Tassili
at similar altitudes (Leredde 1957; Benhouhou
et al. 2003a).
ecologia mediterranea – Vol. 38 (2) – 2012