Ecologia Mediterranea

N. BOUCHENEB, S.S. BENHOUHOU
78
Discussion
The described associations clearly relate to
the altitudinal and edaphic factors at work in
the different wadi types of the Tamanrasset
region. Climatic factors are important in
determining large scale patterns of species
distribution while factors such as topography
and edaphic conditions are more important in
determining vegetation patterns at a smaller
spatial scale (Kadmon & Danin 1999). The
importance of altitude as a major ecological
gradient, which has been shown to affect
species distribution in mountainous regions of
the Saharo-Arabian belt, is an obvious consequence
of the correlation between increased
altitude and higher rainfall (Abd El-Ghani
1996; Danin et al. 1975; Deil 1998; Moustafa
& Klopatek 1995). Altitude is thus here considered
as a “proxy” parameter for explaining
rain variation. Several studies in desert
regions highlight the importance of elevation,
topography, soil texture and water availability
in identifying plant communities and
among others one can mention the desert of
Dubai (Deil & Müller-Hohenstein 1996), the
desert mountains of Oman (Brinkmann et al.
2009), the desert mountains of Yemen (Deil
& Müller-Hohenstein 1985), the Negev desert
of Israel (Danin 1999), Sinai in Egypt
(Moustafa & Klopatek 1995; Moustafa &
Zaghloul 1996) and the Eastern Desert of
Egypt (Abd El-Ghani 1998).
When considering the described associations
in the Tamanrasset region in a wider geographical
context, the isolation of the central
Sahara Mountains in the Saharo-Arabian belt
appears to be a strong factor in leading to the
development of distinctive plant communities.
This is particularly clear with our most alticolous
community, that is: Rhus tripartita-
Olea europaea subsp. laperrinei association.
It is clearly a distinctive association, for which
similar communities in other mountainous
area of the Saharo-Arabian belt are difficult
to find, with the exception of the nearby Air
Mountains, south of the Ahaggar, where common
species such as Rhus tripartita, Rumex
vesicarius L., Senecio spp. and Lavandula
antineae have high frequencies (Anthelme et
al. 2007).
With regard to the Acacia communities, gravelly-sandy
wadis bear the Acacia-Panicum
desertic savannah which is present with several
variants throughout the Sahara (Leonard
2001).
The three associations described in the present
study fit into the Pergulario-Pulicarietea
Quézel 1965, while those in other parts of the
Saharo-Arabian belt are related to the Acacietea
tortilis, which is of East Sudanese distribution
(Deil & Müller-Hohenstein 1985).
Dominant species are the same as those found
in our Acacia communities such as: Acacia
tortilis subsp. raddiana, Acacia ehrenbergiana,
Balanites aegyptiaca, Calotropis procera(Aiton)
W.T. Aiton, Leptadenia pyrotechnica,
Maerua crassifolia, Panicum turgidum
and Zilla spinosa (Abd El-Ghani & Ameur
2003; Ali et al. 2000; Boulos 2008; Shaltout
& Mady 1996; Springuel et al. 1991). Where
relief and substrate are similar, vicarious communities
are well represented across the
whole Saharo-Arabian belt. The Cassia
aschrek-Panicum turgidum association resembles
several communities. In the Hazeva area
of the Negev Desert, Rudich and Danin
(1978) describe a pseudo-savannah of Acacia
tortilis subsp. raddiana associated with
Haloxylon scoparium Pomel and Anabasis
articulata. In the Eastern and Western Desert
of Egypt Acacia raddiana Savi communities
form well defined associations with Tetraena
coccinea (L.) Beier & Thulin (Abd El-Ghani
et al. 2003; Bornkamm & Kehl 1990; Boulos
2008) and Zilla spinosa (Springuel et al.
1991).
The Acacia tortilis subsp. raddiana-Salvadora
persica association is vicarious to the
Acacia ehrenbergiana-Salvadora persica
community found on silty wadis of the
Tihama Mountains in Yemen at altitudes
between 240 and 400 m (Deil & Müller-
Hohenstein 1985).
With regard to the Leptadenia pyrotechnica-
Chrozophora brocchiana association, a similar
community, the Acacia raddiana subsp.
tortilis-Leptadenia pyrotechnica association,
with the same new name that we propose for
our association, is recorded by Abd El-Ghani
& Amer (2003) from alluvial fans along the
Gulf of Suez in the Sinai desert.
The Tamarix aphylla-Farsetia ramosissima
association found on very large wadi beds is
vicarious to several communities found in
similar ecological conditions of the Saharan-
Arabian belt. The closest vicarious community
is probably the Acacia raddiana-Tamarix
nilotica found on main channels of large
wadis in the Hazeva area in the Negev where
three trees are dominant: Acacia tortilis
subsp. raddiana, Balanites aegyptiaca and
ecologia mediterranea – Vol. 38 (2) – 2012