III. PHYSICAL AND VEGETATIONAL ASPECTS OF THE SAHARA
155
The high mountain is characterized on the biogeographic plan as an
interaction of the Saharo-sindian, Mediterranean, and African lines.
Those species of Saharo-sindian stock, not numerous, live only in the
groups of small pools located outside the wadi beds. At Hoggar, the Mediterranean influences predominate as well as at Tibesti. Between 1800 and
2400 meters are found the species of tropical stock which dominate, and
on the summits are found the mediterranean species.
e. The Meridional Sahara. This region constitutes the most arid part
of the Sahara. The hyperarid zones are composed of, from east to west,
Djourab, Ténéré, Tanezrouft, Azaouad, and Majâbat. They are characterized by the uniformity and the extreme poverty of their flora. Two groups
of psammophiles, however, can appear: the association of Aristida
acutiflora-Indigofera
semitrijuga and the association of Danthonia
forskalii-Plantago ciliata.
Monod (1958), over a surface nearly 200,000 km
2
in Majâbat-alKoubrâ, counted seven species of Phanerogams, viz., Aristida pungens,
A. acutiflora, Cornulaca monacantha, Cistanche phelypaea, Danthonia
fragilis, Neurada procumbens, and Malcolmia aegyptiaca. In this region,
this single flora constitutes a locally diffuse vegetation, an aspect of a
steppe.
On the other hand, in Tanezrouft, in Ténéré (Mission Berliet, 1962)
and in Borkou, Quézel (1965) observed only very loose populations in
examining 50 to 100 km
2
for Aristida plumosa, A. acutiflora, Boerhavia
repens, Neurada procumbens.
5. Conclusions
The Saharan is first fixed by the general climate and arbitrarily by the
localized edaphic factors in the particular zones : sources of water, borders
of wadis, terrain, salt beds, ergs.
The historical interpretation takes into consideration the floristic
parentage. Thus the mesogeean Sahara comes from the holarctic domain
as well as do the meridional and tropical Sahara come from the palearctic
domain. It is shown even in the vegetation of the high mountains: in the
central Sahara and in particular in Hoggar, the Mediterranean elements
predominate, and the endemism is composed essentially of Mediterranean
types. As in Air and Tibesti, the tropical influences are important.
C. THE SOILS—ECOLOGICAL CHARACTERS
The Saharan soils have variable physicochemical conditions from one
type to another (Ozenda, 1958). In general, they have sufficient amounts
of nutrients indispensable for plants. Because of the absence of infiltration
155
The high mountain is characterized on the biogeographic plan as an
interaction of the Saharo-sindian, Mediterranean, and African lines.
Those species of Saharo-sindian stock, not numerous, live only in the
groups of small pools located outside the wadi beds. At Hoggar, the Mediterranean influences predominate as well as at Tibesti. Between 1800 and
2400 meters are found the species of tropical stock which dominate, and
on the summits are found the mediterranean species.
e. The Meridional Sahara. This region constitutes the most arid part
of the Sahara. The hyperarid zones are composed of, from east to west,
Djourab, Ténéré, Tanezrouft, Azaouad, and Majâbat. They are characterized by the uniformity and the extreme poverty of their flora. Two groups
of psammophiles, however, can appear: the association of Aristida
acutiflora-Indigofera
semitrijuga and the association of Danthonia
forskalii-Plantago ciliata.
Monod (1958), over a surface nearly 200,000 km
2
in Majâbat-alKoubrâ, counted seven species of Phanerogams, viz., Aristida pungens,
A. acutiflora, Cornulaca monacantha, Cistanche phelypaea, Danthonia
fragilis, Neurada procumbens, and Malcolmia aegyptiaca. In this region,
this single flora constitutes a locally diffuse vegetation, an aspect of a
steppe.
On the other hand, in Tanezrouft, in Ténéré (Mission Berliet, 1962)
and in Borkou, Quézel (1965) observed only very loose populations in
examining 50 to 100 km
2
for Aristida plumosa, A. acutiflora, Boerhavia
repens, Neurada procumbens.
5. Conclusions
The Saharan is first fixed by the general climate and arbitrarily by the
localized edaphic factors in the particular zones : sources of water, borders
of wadis, terrain, salt beds, ergs.
The historical interpretation takes into consideration the floristic
parentage. Thus the mesogeean Sahara comes from the holarctic domain
as well as do the meridional and tropical Sahara come from the palearctic
domain. It is shown even in the vegetation of the high mountains: in the
central Sahara and in particular in Hoggar, the Mediterranean elements
predominate, and the endemism is composed essentially of Mediterranean
types. As in Air and Tibesti, the tropical influences are important.
C. THE SOILS—ECOLOGICAL CHARACTERS
The Saharan soils have variable physicochemical conditions from one
type to another (Ozenda, 1958). In general, they have sufficient amounts
of nutrients indispensable for plants. Because of the absence of infiltration