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In-Depth Information
reconstruct the vegetation history of the Sahara. Early studies by Pons and Quezel,
although soon superseded, showed the pollen bearing potential of even such unlikely
samples as calcified crocodile coprolites from the Hoggar (Pons and Quezel,
1957
;
Pons and Quezel,
1958
). During intervals when the winter westerlies brought rain to
the piedmont slopes of the Saharan uplands, it was perhaps possible for Mediterranean
olive trees to migrate along suitable river valleys into the southern Sahara (Quezel
and Martinez,
1958
-
1959
;Quezel and Martinez,
1962
;Wickens,
1976a
;Wickens,
1976b
).
Olea laperrinei
, for instance, grows today on the slopes of Jebel Marra
volcanic caldera in western Sudan (Wickens,
1976a
;Wickens,
1976b
)aswellas
high on the bouldery, granite slopes of the northern Aır Mountains of Niger (Quezel,
1962
).
Sporadic pollen identifications from ill-dated and often nearly sterile deposits even-
tually gave way to a more rigorous concern for the ecological requirements of the
existing flora, the present-day pollen rain and the need for coring and sampling at
more appropriate sites (see
Chapter 16
). Fran¸oise Beucher's floristic and palynolo-
gical survey of the Saoura Valley (Beucher,
1971
) is an excellent example of the first
concern, and Jean Maley's early research into the Holocene history of the Chad flora
exemplifies the last two preoccupations (Maley,
1981
). French scholars and official
grant-giving bodies in and outside of France began to recognise that pollen studies are
necessarily long and slow, so the plethora of rapidly published but scientifically dubi-
ous studies of the early 1960s later yielded to a few weighty monographs (Bonnefille,
1972
;Maley,
1981
), together with some more concise overviews of the vegetation
history of East and North Africa (Rossignol and Maley,
1969
; Livingstone,
1975
;
Bonnefille,
1976
).
5.2.4 Prehistoric occupation of the Sahara: Neolithic grazing
and desertification
Geomorphic and paleobotanical studies of the complex array of Saharan Quaternary
fluviatile, lacustrine and wind-blown deposits indicated that prehistoric settlement of
the region took place against a background of alternating arid and less arid conditions.
The less arid phases were ones of high lake levels, of soil formation, of fluvial
activity, and of the migration of plants, animals and small bands of humans into
the now arid desert plains. The abundance of Neolithic occupation sites in now arid
and empty parts of the Sahara (Monod,
1958
; Maley et al.,
1970
; Delibrias et al.,
1976
; Clark,
1980
; Clark et al.,
2008
) should not be taken to imply that overgrazing
by domesticated herds of Neolithic cattle, sheep and goats created the desert we
know today, for the great sand seas, or ergs, were already in existence by Early
Stone Age times (Alimen,
1955
), more than 500,000 years ago (Clark,
1975
). There
were sound reasons why Neolithic pastoralists and their herds preferred the sparse
pastures of the lake-studded plains around Tibesti, the Hoggar (Rognon,
1967
), the Aır
