106
CLAUDE J. GRENOT
of 1600 km, and from the Atlantic Ocean to the Red Sea roughly 4500
km.
The boundaries of the Sahara are essentially climatic. It lies between
two zones of regular rainfalls : to the north, the Mediterranean Africa, and
to the south, the Sudanese Africa.
Depending upon which scientific discipline is involved, meterology,
geology, botany, zoology, or ethnography, the boundaries of the Sahara
are defined somewhat differently (Zolotarevsky and Murat, 1938; Dubief,
1953; Capot-Rey, 1952; Emberger, 1955; UNESCO-FAO, 1963; Monod,
1968). However, they are all more or less identical which is clear proof
of the reality of the Saharan entity.
To the north, the boundary formed by the Saharan Atlas is quite evident; to the south, however, it is only an approximation, as one passes
progressively from the desert to the Sahel (the littoral of the desert).
Capot-Rey (1952) selected as a septentrional boundary of the Sahara the
southern margin of the growth of Esparto grass, and as a meridional one,
the margin delineated by the growth of the had (Cornulaca monacantha,
a Saharo-sindian Chenopodiacea) and the cram-cram (Cenchrus biflorus,
a Sudanese grass).
From the north to the south, we find a relatively humid zone with plants
forming an open steppe which becomes progressively thinner. The vegetation passes from the "diffuse" type to the "constricted," the latter being
typical of a true desert (Monod, 1954).
The 10-cm isohyet curve seems quite approximately to delineate the
boundaries of the true desert (Fig. 1). The vegetation of the "constricted"
type is typical of any region receiving less than 3 cm of precipitation per
year.
The Sahara can, arbitrarily, be divided into several regions. The phytogeographic classification established by Monod (1957) and later used by
Quézel (1965), divides it into seven principal domains:
1. The domain of the septentrional Sahara
2. The domain of the north occidental Sahara
3. The domain of the oceanic Sahara
4. The domain of the high mountains
5. The domain of the central Sahara
6. The domain of the occidental Sahara
7. The domain of the meridional Sahara, prolonged by the semiarid
Sahelo-Sudanese region.
To the east, the Sahara stretches out into an extremely arid region, the
Libyan Desert, which is separated from the Nubian Desert by the green
valley of the Nile.
CLAUDE J. GRENOT
of 1600 km, and from the Atlantic Ocean to the Red Sea roughly 4500
km.
The boundaries of the Sahara are essentially climatic. It lies between
two zones of regular rainfalls : to the north, the Mediterranean Africa, and
to the south, the Sudanese Africa.
Depending upon which scientific discipline is involved, meterology,
geology, botany, zoology, or ethnography, the boundaries of the Sahara
are defined somewhat differently (Zolotarevsky and Murat, 1938; Dubief,
1953; Capot-Rey, 1952; Emberger, 1955; UNESCO-FAO, 1963; Monod,
1968). However, they are all more or less identical which is clear proof
of the reality of the Saharan entity.
To the north, the boundary formed by the Saharan Atlas is quite evident; to the south, however, it is only an approximation, as one passes
progressively from the desert to the Sahel (the littoral of the desert).
Capot-Rey (1952) selected as a septentrional boundary of the Sahara the
southern margin of the growth of Esparto grass, and as a meridional one,
the margin delineated by the growth of the had (Cornulaca monacantha,
a Saharo-sindian Chenopodiacea) and the cram-cram (Cenchrus biflorus,
a Sudanese grass).
From the north to the south, we find a relatively humid zone with plants
forming an open steppe which becomes progressively thinner. The vegetation passes from the "diffuse" type to the "constricted," the latter being
typical of a true desert (Monod, 1954).
The 10-cm isohyet curve seems quite approximately to delineate the
boundaries of the true desert (Fig. 1). The vegetation of the "constricted"
type is typical of any region receiving less than 3 cm of precipitation per
year.
The Sahara can, arbitrarily, be divided into several regions. The phytogeographic classification established by Monod (1957) and later used by
Quézel (1965), divides it into seven principal domains:
1. The domain of the septentrional Sahara
2. The domain of the north occidental Sahara
3. The domain of the oceanic Sahara
4. The domain of the high mountains
5. The domain of the central Sahara
6. The domain of the occidental Sahara
7. The domain of the meridional Sahara, prolonged by the semiarid
Sahelo-Sudanese region.
To the east, the Sahara stretches out into an extremely arid region, the
Libyan Desert, which is separated from the Nubian Desert by the green
valley of the Nile.